PSU Design...

[Fred Bloggs]

On Tuesday, May 2, 2023 at 4:20:08 PM UTC-4, John Larkin wrote:

On Tue, 2 May 2023 11:50:04 -0700 (PDT), Fred Bloggs
bloggs.fred...@gmail.com> wrote:
On Tuesday, May 2, 2023 at 2:43:17?PM UTC-4, John Larkin wrote:
On Tue, 2 May 2023 10:56:14 -0700 (PDT), Fred Bloggs
bloggs.fred...@gmail.com> wrote:

On Tuesday, May 2, 2023 at 12:10:16?AM UTC-4, Anthony William Sloman wrote:
On Tuesday, May 2, 2023 at 4:46:52?AM UTC+10, Cursitor Doom wrote:
Gentlemen,

I know this will upset and disappoint a certain antipodean contributor
here, but I would like, if I may, to discuss electronic design for a
moment.

This concerns a linear power supply regulator board from a Tek 7000
series scope. Some of you may recall my infatuation with vintage test
gear and this is the latest subject for attention. This board produces
the following voltages: +130V, +50V, -50V, +15V, -15V and +5V
(regulated with feedback sensing from the downstream circuitry).

The first question I have is why would the designer come up with this
scheme where there are multiple interdependencies between the 6 output
voltages?
Hard to say. It\'s clearly a very old design, and the schematic you\'ve posted isn\'t complete - and doesn\'t have a date on it.

Makes no difference, it\'s still golden.


There\'s no voltage reference shown anywhere on the part of the schematic you have posted, so trying to second-guess why the designer came up with what\'s shown here would be a waste of time.

Those things that look like diodes with designator \'VR\' are zeners, VR means voltage reference.
The CR things are crystal rectifiers.

In those days, D meant dynamotor, a type of dc/dc converter.

I don\'t think the circuit is that old. It post dates the invention of the transistor. Probably designed in the 70s.
It\'s full of CR things. Not a D in sight.

Resistors are 4.7k, not the dreadful 4k7.

C985 is .0047; nanofarads hadn\'t been invented yet.

They do avoid 4-way connections, which people did in the days of
hand-drawn schamatics, when connection dots would fall off the page.

What\'s going on with Q829?

I\'m sure you would recognize it when it\'s pointed out to you. The Q-829, -835, -827 trio is that active feedback bias technique used to stabilize the DC bias point of Q835 against variation in beta and VBE with temperature and I suppose VCE too. It\'s output in the form of current is going out that jack to the left. It\'s input is coming from there too. The collector of Q829 is just a take-off point for that rectified DC being used to power the difference amplifier to the right, it\'s not doing anything to it.

I hate the upside-down ground rakes.

 

[John Larkin]

On Fri, 5 May 2023 10:20:43 -0700 (PDT), Fred Bloggs
<bloggs.fredbloggs.fred@gmail.com> wrote:

On Tuesday, May 2, 2023 at 4:20:08?PM UTC-4, John Larkin wrote:
On Tue, 2 May 2023 11:50:04 -0700 (PDT), Fred Bloggs
bloggs.fred...@gmail.com> wrote:
On Tuesday, May 2, 2023 at 2:43:17?PM UTC-4, John Larkin wrote:
On Tue, 2 May 2023 10:56:14 -0700 (PDT), Fred Bloggs
bloggs.fred...@gmail.com> wrote:

On Tuesday, May 2, 2023 at 12:10:16?AM UTC-4, Anthony William Sloman wrote:
On Tuesday, May 2, 2023 at 4:46:52?AM UTC+10, Cursitor Doom wrote:
Gentlemen,

I know this will upset and disappoint a certain antipodean contributor
here, but I would like, if I may, to discuss electronic design for a
moment.

This concerns a linear power supply regulator board from a Tek 7000
series scope. Some of you may recall my infatuation with vintage test
gear and this is the latest subject for attention. This board produces
the following voltages: +130V, +50V, -50V, +15V, -15V and +5V
(regulated with feedback sensing from the downstream circuitry).

The first question I have is why would the designer come up with this
scheme where there are multiple interdependencies between the 6 output
voltages?
Hard to say. It\'s clearly a very old design, and the schematic you\'ve posted isn\'t complete - and doesn\'t have a date on it.

Makes no difference, it\'s still golden.


There\'s no voltage reference shown anywhere on the part of the schematic you have posted, so trying to second-guess why the designer came up with what\'s shown here would be a waste of time.

Those things that look like diodes with designator \'VR\' are zeners, VR means voltage reference.
The CR things are crystal rectifiers.

In those days, D meant dynamotor, a type of dc/dc converter.

I don\'t think the circuit is that old. It post dates the invention of the transistor. Probably designed in the 70s.
It\'s full of CR things. Not a D in sight.

Resistors are 4.7k, not the dreadful 4k7.

C985 is .0047; nanofarads hadn\'t been invented yet.

They do avoid 4-way connections, which people did in the days of
hand-drawn schamatics, when connection dots would fall off the page.

What\'s going on with Q829?

I\'m sure you would recognize it when it\'s pointed out to you. The Q-829, -835, -827 trio is that active feedback bias technique used to stabilize the DC bias point of Q835 against variation in beta and VBE with temperature and I suppose VCE too. It\'s output in the form of current is going out that jack to the left. It\'s input is coming from there too. The collector of Q829 is just a take-off point for that rectified DC being used to power the difference amplifier to the right, it\'s not doing anything to it.

I meant the three dots on the base lead.

 

[piglet]

On 05/05/2023 19:10, John Larkin wrote:

On Fri, 5 May 2023 10:20:43 -0700 (PDT), Fred Bloggs
bloggs.fredbloggs.fred@gmail.com> wrote:

On Tuesday, May 2, 2023 at 4:20:08?PM UTC-4, John Larkin wrote:
On Tue, 2 May 2023 11:50:04 -0700 (PDT), Fred Bloggs
bloggs.fred...@gmail.com> wrote:
On Tuesday, May 2, 2023 at 2:43:17?PM UTC-4, John Larkin wrote:
On Tue, 2 May 2023 10:56:14 -0700 (PDT), Fred Bloggs
bloggs.fred...@gmail.com> wrote:

On Tuesday, May 2, 2023 at 12:10:16?AM UTC-4, Anthony William Sloman wrote:
On Tuesday, May 2, 2023 at 4:46:52?AM UTC+10, Cursitor Doom wrote:
Gentlemen,

I know this will upset and disappoint a certain antipodean contributor
here, but I would like, if I may, to discuss electronic design for a
moment.

This concerns a linear power supply regulator board from a Tek 7000
series scope. Some of you may recall my infatuation with vintage test
gear and this is the latest subject for attention. This board produces
the following voltages: +130V, +50V, -50V, +15V, -15V and +5V
(regulated with feedback sensing from the downstream circuitry).

The first question I have is why would the designer come up with this
scheme where there are multiple interdependencies between the 6 output
voltages?
Hard to say. It\'s clearly a very old design, and the schematic you\'ve posted isn\'t complete - and doesn\'t have a date on it.

Makes no difference, it\'s still golden.


There\'s no voltage reference shown anywhere on the part of the schematic you have posted, so trying to second-guess why the designer came up with what\'s shown here would be a waste of time.

Those things that look like diodes with designator \'VR\' are zeners, VR means voltage reference.
The CR things are crystal rectifiers.

In those days, D meant dynamotor, a type of dc/dc converter.

I don\'t think the circuit is that old. It post dates the invention of the transistor. Probably designed in the 70s.
It\'s full of CR things. Not a D in sight.

Resistors are 4.7k, not the dreadful 4k7.

C985 is .0047; nanofarads hadn\'t been invented yet.

They do avoid 4-way connections, which people did in the days of
hand-drawn schamatics, when connection dots would fall off the page.

What\'s going on with Q829?

I\'m sure you would recognize it when it\'s pointed out to you. The Q-829, -835, -827 trio is that active feedback bias technique used to stabilize the DC bias point of Q835 against variation in beta and VBE with temperature and I suppose VCE too. It\'s output in the form of current is going out that jack to the left. It\'s input is coming from there too. The collector of Q829 is just a take-off point for that rectified DC being used to power the difference amplifier to the right, it\'s not doing anything to it.



I meant the three dots on the base lead.

Yandex rained down some spare decimal points?

The schematic on TekWiki is clearer and does not show those dots. Q835
et al are the graticule lamps dimmer.

piglet

 

[Fred Bloggs]

On Friday, May 5, 2023 at 2:10:37 PM UTC-4, John Larkin wrote:

On Fri, 5 May 2023 10:20:43 -0700 (PDT), Fred Bloggs
bloggs.fred...@gmail.com> wrote:
On Tuesday, May 2, 2023 at 4:20:08?PM UTC-4, John Larkin wrote:
On Tue, 2 May 2023 11:50:04 -0700 (PDT), Fred Bloggs
bloggs.fred...@gmail.com> wrote:
On Tuesday, May 2, 2023 at 2:43:17?PM UTC-4, John Larkin wrote:
On Tue, 2 May 2023 10:56:14 -0700 (PDT), Fred Bloggs
bloggs.fred...@gmail.com> wrote:

On Tuesday, May 2, 2023 at 12:10:16?AM UTC-4, Anthony William Sloman wrote:
On Tuesday, May 2, 2023 at 4:46:52?AM UTC+10, Cursitor Doom wrote:
Gentlemen,

I know this will upset and disappoint a certain antipodean contributor
here, but I would like, if I may, to discuss electronic design for a
moment.

This concerns a linear power supply regulator board from a Tek 7000
series scope. Some of you may recall my infatuation with vintage test
gear and this is the latest subject for attention. This board produces
the following voltages: +130V, +50V, -50V, +15V, -15V and +5V
(regulated with feedback sensing from the downstream circuitry).

The first question I have is why would the designer come up with this
scheme where there are multiple interdependencies between the 6 output
voltages?
Hard to say. It\'s clearly a very old design, and the schematic you\'ve posted isn\'t complete - and doesn\'t have a date on it.

Makes no difference, it\'s still golden.


There\'s no voltage reference shown anywhere on the part of the schematic you have posted, so trying to second-guess why the designer came up with what\'s shown here would be a waste of time.

Those things that look like diodes with designator \'VR\' are zeners, VR means voltage reference.
The CR things are crystal rectifiers.

In those days, D meant dynamotor, a type of dc/dc converter.

I don\'t think the circuit is that old. It post dates the invention of the transistor. Probably designed in the 70s.
It\'s full of CR things. Not a D in sight.

Resistors are 4.7k, not the dreadful 4k7.

C985 is .0047; nanofarads hadn\'t been invented yet.

They do avoid 4-way connections, which people did in the days of
hand-drawn schamatics, when connection dots would fall off the page.

What\'s going on with Q829?

I\'m sure you would recognize it when it\'s pointed out to you. The Q-829, -835, -827 trio is that active feedback bias technique used to stabilize the DC bias point of Q835 against variation in beta and VBE with temperature and I suppose VCE too. It\'s output in the form of current is going out that jack to the left. It\'s input is coming from there too. The collector of Q829 is just a take-off point for that rectified DC being used to power the difference amplifier to the right, it\'s not doing anything to it.


I meant the three dots on the base lead.

That\'s a new one on me, can\'t really make them out. I have no idea.

 

[John Larkin]

On Fri, 5 May 2023 19:48:14 +0100, piglet <erichpwagner@hotmail.com>
wrote:

On 05/05/2023 19:10, John Larkin wrote:
On Fri, 5 May 2023 10:20:43 -0700 (PDT), Fred Bloggs
bloggs.fredbloggs.fred@gmail.com> wrote:

On Tuesday, May 2, 2023 at 4:20:08?PM UTC-4, John Larkin wrote:
On Tue, 2 May 2023 11:50:04 -0700 (PDT), Fred Bloggs
bloggs.fred...@gmail.com> wrote:
On Tuesday, May 2, 2023 at 2:43:17?PM UTC-4, John Larkin wrote:
On Tue, 2 May 2023 10:56:14 -0700 (PDT), Fred Bloggs
bloggs.fred...@gmail.com> wrote:

On Tuesday, May 2, 2023 at 12:10:16?AM UTC-4, Anthony William Sloman wrote:
On Tuesday, May 2, 2023 at 4:46:52?AM UTC+10, Cursitor Doom wrote:
Gentlemen,

I know this will upset and disappoint a certain antipodean contributor
here, but I would like, if I may, to discuss electronic design for a
moment.

This concerns a linear power supply regulator board from a Tek 7000
series scope. Some of you may recall my infatuation with vintage test
gear and this is the latest subject for attention. This board produces
the following voltages: +130V, +50V, -50V, +15V, -15V and +5V
(regulated with feedback sensing from the downstream circuitry).

The first question I have is why would the designer come up with this
scheme where there are multiple interdependencies between the 6 output
voltages?
Hard to say. It\'s clearly a very old design, and the schematic you\'ve posted isn\'t complete - and doesn\'t have a date on it.

Makes no difference, it\'s still golden.


There\'s no voltage reference shown anywhere on the part of the schematic you have posted, so trying to second-guess why the designer came up with what\'s shown here would be a waste of time.

Those things that look like diodes with designator \'VR\' are zeners, VR means voltage reference.
The CR things are crystal rectifiers.

In those days, D meant dynamotor, a type of dc/dc converter.

I don\'t think the circuit is that old. It post dates the invention of the transistor. Probably designed in the 70s.
It\'s full of CR things. Not a D in sight.

Resistors are 4.7k, not the dreadful 4k7.

C985 is .0047; nanofarads hadn\'t been invented yet.

They do avoid 4-way connections, which people did in the days of
hand-drawn schamatics, when connection dots would fall off the page.

What\'s going on with Q829?

I\'m sure you would recognize it when it\'s pointed out to you. The Q-829, -835, -827 trio is that active feedback bias technique used to stabilize the DC bias point of Q835 against variation in beta and VBE with temperature and I suppose VCE too. It\'s output in the form of current is going out that jack to the left. It\'s input is coming from there too. The collector of Q829 is just a take-off point for that rectified DC being used to power the difference amplifier to the right, it\'s not doing anything to it.



I meant the three dots on the base lead.


Yandex rained down some spare decimal points?

The schematic on TekWiki is clearer and does not show those dots.

Oh, I thought it might be a ferrite bead or something.

Q835
et al are the graticule lamps dimmer.

Was that an old scope with an external edge-lit plastic graticule? Or
the later internal one?

piglet

 

[Cursitor Doom]

On Fri, 5 May 2023 06:04:43 -0700 (PDT), Anthony William Sloman
<bill.sloman@ieee.org> wrote:

On Friday, May 5, 2023 at 7:39:05?PM UTC+10, piglet wrote:
On 05/05/2023 7:10 am, Anthony William Sloman wrote:

Not exactly. VR890 seems to be setting up a -9.0V reference for the dual transistor Q886 to sense, and R880,R881 and R882 divide down the -50V rail to produce a matching -9.0V but R883 (to 0V) and R884 to -53V suck out a bit of current through CR883 which complicates the situation.

If that\'s a design, I\'d hate to see an improvisation.

That\'s a really component-rich design. It was probably much-tinkered.

And not well-thought out.

CR883 would normally be reverse biased, it is there to cope with the
remote sense line getting disconnected.

I thought of that after I\'d made my post, which was a bit embarrassing. European circuit design has adopted a number of conventions that make that kind of mistake less likely.

The schematic is not drawn for great clarity but I am not critical of the design. Looks competent me and has interlocks. The use of higher voltage rails as current sources to the diff amps make it look more confusing than it is.

There are couple of PNP transistors used as current sources on the schematic, but they aren\'t drawn in a way that makes this clear.

There is a rule of thumb that says if you can\'t draw your circuit in a way that makes it clear to other people what it is doing, you probably don\'t have a clear idea of it\'s operation yourself, but American circuit diagrams from that period were pretty much uninformly horrible.

Well, I\'ve never seen anything like this before in a linear PSU from a
respected company. It\'s almost as if they were forced to use
transformers with not enough suitable secondary windings. There\'s a
revision date on this board: 1971.

 

[Cursitor Doom]

On Thu, 04 May 2023 20:54:26 -0700, John Larkin
<jlarkin@highlandSNIPMEtechnology.com> wrote:

On Thu, 4 May 2023 22:40:27 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 2023-05-04 20:22, John Larkin wrote:
On Thu, 4 May 2023 12:57:03 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 2023-05-04 12:26, John Larkin wrote:
On Thu, 4 May 2023 10:26:55 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 2023-05-04 08:39, John Larkin wrote:
On Thu, 4 May 2023 00:32:10 -0400, chuck <donnyduck@gmail.com> wrote:

On 02/05/2023 5:53 p.m., John Larkin wrote:
On Tue, 2 May 2023 16:23:53 -0400, chuck <donnyduck@gmail.com> wrote:

On 02/05/2023 2:43 p.m., John Larkin wrote:


The CR things are crystal rectifiers.




Not quite.


CR = CURRENT RECTIFIER

This design intent was to control startup sequence to ensure the highest
voltage source enables the 50V which enables the 15V.

If the HV was slow in rising, some circuit that uses both supply
voltages would see that as a polarity reversal.

For 3 terminal LDO\'s they mitigate this prompting users to add a reverse
diode from input to output so if the higher input voltage goes down
fast, the diode will protect BE junctions from excessive reverse voltage
|Vr| > 5V.

It was a good question that did not deserve snarky responses.

Tony Stewart
EE since 1975

No snark at all. Crystal Rectifier was the initial meaning of CR.

https://www.reddit.com/r/diyelectronics/comments/yl5s28/whats_this_strange_component_designator_cr1/

https://en.wikipedia.org/wiki/Crystal_detector

https://en.wikipedia.org/wiki/Diode

Rad Lab vol 15 is titled \"Crystal Rectifiers.\" Point-contact diode
mixers were one of the three keys to microwave radar, and radar won
WWII.

The diodes in the Tek schematic are not current regulator diodes,
which are actually a form of jfet. I doubt they existed then. I have
not previously heard the term CURRENT RECTIFIER.


John Larkin
EE since 1966


John I guess I started design in Aerospace at the right time in 1975.
and it was probably my draftsman who said it stood for CURRENT RECTIFIER
which a common descriptor. Although I read most of the Mil-Specs and STD
HBBK\'s from our vast library at Bristol Aerospace, I can\'t recall seeing
it there. It was nice to have any test equipment you needed.

Here is the TEK7904 mainframe service manual.
https://w140.com/Tek_7904_OCRed_by_Tabalabs.pdf


I guess you youngsters don\'t remember point-contact rectifiers,
selenium rectifiers, vacuum tube rectifiers, copper oxide rectifiers,
tungar rectifiers, mercury rectifiers, ignitron rectifiers, vibrator
rectifiers, synchronous rectifiers, foxhole (rusty razor blade)
rectifiers, galena rectifiers, or electrolytic rectifiers.

I actually saw a tungar rectifier in operation when I was a kid. In a
gas station.

There were germanium, silicon, and gallium arsenide rectifiers in
WWII. I *don\'t* remember WWII.


I\'m a skosh younger than you, but I\'ve built things with selenium, tube,
point contact, synchronous, and galena rectifiers. I have a couple of
dozen point contact diodes in a Lista cabinet bin (1N34A, 1N38B, and
1N21C).

Your synchronous rectifiers were probably mosfets, but I was thinking
of the motor-driven mechanical contact types.

(Somebody built a DRAM with leaded capacitors on a spinning disk.)

I think that was John D. Atanasoff (of Atanasoff-Berry Computer fame).


One cool device was a DPDT vibrator, sometimes used in car radios. One
set of contacts pushed 12 volts into a transformer primary and the
other set rectified the secondary. Old tube car radios had some
interesting technology. I used to get them free from junkyards.

Yup. As a teenager, I had an old T19 Mk III tank transceiver that
(iirc) had a companion vibrator supply. Interesting gizmo--I never did
get it to work. I remember a weird E1148 VHF superregen oscillator tube
with two caps on it.


(I once needed some vibrators to help parts in tubes slide down
low-slope feeders on a pick-and-place line, for a friend who had an
assembly shop. I found a suitable gadget at Good Vibrations, a
ladies\', umm, accessory store. That was fun.)



Of course the galena was just for fun, and never actually did very much.
The seleniums and tubes were salvaged from old TVs when I was a boy.
(It was a good thing for me that frying seleniums smell so horrible--I
didn\'t realize that the fumes were dangerous.)

There are still things that tubes are unbeatable at. My last tube
circuit used an 811A to control a grid in an electrostatic drift
chamber--it needed to switch some hundreds of volts, and then go
completely away, i.e. have very low leakage and capacitance when off.

(Of course, that was in about 1990.)

My tube-type GDOs are some of my favorite instruments.

Some of the Keithley electrometers used a special electrometer tube.
Mine uses an early vintage mosfet.

I have one of each: a 405 and a 610C like yours. The 405 works on the
100-fA scale if you let it warm up for an hour or so.

https://www.dropbox.com/s/lo8xsx2x07b4zy4/Welwyn_1G_Keithley.jpg?raw=1

When I first played with mosfets I built a voltage follower and
accidentally left the gate open. The source voltage froze and didn\'t
change a bit. I was amazed. Now one can do cool things with a 2N7000.

If you can find one that isn\'t gate-protected, these days. I have a
reel of 2N7002E\'s because NXP discontinued them.


My 610 doesn\'t work in fast mode, just goes bonkers. Sometimes a
measurement takes half an hour to settle and I have to walk around my
office holding a ground wire. Does yours work in fast mode?


Generally, but not on the three bottom ranges (10, 30, and 100 fA FS).
The 10 fA scale is apparently just there to decorate the front
panel--it\'s too unstable to be useful even in slow mode.

Possibly hooking up a LabJack to the analog output and averaging awhile
might fix it, but if I needed to do that I\'d certainly wire up something
dead bug style in a cast-aluminum stomp box instead of using the Keithley.

Sometime in my declining years I might retrofit my old 602, which is
sort of like a more primitive 610C that runs off a zillion dry cells.

I\'d probably pick a 100-pf polystyrene cap out of my drawer, wire it up
as a current integrator with something like an LMC6001 op amp, and
connect it straight to the input. with some very low leakage reset switch.

Then I\'d do a F/V for higher currents, and differentiate the ramp for
lower ones.

Cheers

Phil Hobbs

One way to measure low current is to let it dump into a cap for an
hour or a week, and then measure the voltage on the cap. That will
work to aA\'s.

Seriously? I\'m surprised there\'s no mention of this in any of the
Keighley books. What sort of cap, though?

 

[John Larkin]

On Sun, 07 May 2023 13:43:18 +0100, Cursitor Doom <cd@notformail.com>
wrote:

On Thu, 04 May 2023 20:54:26 -0700, John Larkin
jlarkin@highlandSNIPMEtechnology.com> wrote:

On Thu, 4 May 2023 22:40:27 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 2023-05-04 20:22, John Larkin wrote:
On Thu, 4 May 2023 12:57:03 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 2023-05-04 12:26, John Larkin wrote:
On Thu, 4 May 2023 10:26:55 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 2023-05-04 08:39, John Larkin wrote:
On Thu, 4 May 2023 00:32:10 -0400, chuck <donnyduck@gmail.com> wrote:

On 02/05/2023 5:53 p.m., John Larkin wrote:
On Tue, 2 May 2023 16:23:53 -0400, chuck <donnyduck@gmail.com> wrote:

On 02/05/2023 2:43 p.m., John Larkin wrote:


The CR things are crystal rectifiers.




Not quite.


CR = CURRENT RECTIFIER

This design intent was to control startup sequence to ensure the highest
voltage source enables the 50V which enables the 15V.

If the HV was slow in rising, some circuit that uses both supply
voltages would see that as a polarity reversal.

For 3 terminal LDO\'s they mitigate this prompting users to add a reverse
diode from input to output so if the higher input voltage goes down
fast, the diode will protect BE junctions from excessive reverse voltage
|Vr| > 5V.

It was a good question that did not deserve snarky responses.

Tony Stewart
EE since 1975

No snark at all. Crystal Rectifier was the initial meaning of CR.

https://www.reddit.com/r/diyelectronics/comments/yl5s28/whats_this_strange_component_designator_cr1/

https://en.wikipedia.org/wiki/Crystal_detector

https://en.wikipedia.org/wiki/Diode

Rad Lab vol 15 is titled \"Crystal Rectifiers.\" Point-contact diode
mixers were one of the three keys to microwave radar, and radar won
WWII.

The diodes in the Tek schematic are not current regulator diodes,
which are actually a form of jfet. I doubt they existed then. I have
not previously heard the term CURRENT RECTIFIER.


John Larkin
EE since 1966


John I guess I started design in Aerospace at the right time in 1975.
and it was probably my draftsman who said it stood for CURRENT RECTIFIER
which a common descriptor. Although I read most of the Mil-Specs and STD
HBBK\'s from our vast library at Bristol Aerospace, I can\'t recall seeing
it there. It was nice to have any test equipment you needed.

Here is the TEK7904 mainframe service manual.
https://w140.com/Tek_7904_OCRed_by_Tabalabs.pdf


I guess you youngsters don\'t remember point-contact rectifiers,
selenium rectifiers, vacuum tube rectifiers, copper oxide rectifiers,
tungar rectifiers, mercury rectifiers, ignitron rectifiers, vibrator
rectifiers, synchronous rectifiers, foxhole (rusty razor blade)
rectifiers, galena rectifiers, or electrolytic rectifiers.

I actually saw a tungar rectifier in operation when I was a kid. In a
gas station.

There were germanium, silicon, and gallium arsenide rectifiers in
WWII. I *don\'t* remember WWII.


I\'m a skosh younger than you, but I\'ve built things with selenium, tube,
point contact, synchronous, and galena rectifiers. I have a couple of
dozen point contact diodes in a Lista cabinet bin (1N34A, 1N38B, and
1N21C).

Your synchronous rectifiers were probably mosfets, but I was thinking
of the motor-driven mechanical contact types.

(Somebody built a DRAM with leaded capacitors on a spinning disk.)

I think that was John D. Atanasoff (of Atanasoff-Berry Computer fame).


One cool device was a DPDT vibrator, sometimes used in car radios. One
set of contacts pushed 12 volts into a transformer primary and the
other set rectified the secondary. Old tube car radios had some
interesting technology. I used to get them free from junkyards.

Yup. As a teenager, I had an old T19 Mk III tank transceiver that
(iirc) had a companion vibrator supply. Interesting gizmo--I never did
get it to work. I remember a weird E1148 VHF superregen oscillator tube
with two caps on it.


(I once needed some vibrators to help parts in tubes slide down
low-slope feeders on a pick-and-place line, for a friend who had an
assembly shop. I found a suitable gadget at Good Vibrations, a
ladies\', umm, accessory store. That was fun.)



Of course the galena was just for fun, and never actually did very much.
The seleniums and tubes were salvaged from old TVs when I was a boy.
(It was a good thing for me that frying seleniums smell so horrible--I
didn\'t realize that the fumes were dangerous.)

There are still things that tubes are unbeatable at. My last tube
circuit used an 811A to control a grid in an electrostatic drift
chamber--it needed to switch some hundreds of volts, and then go
completely away, i.e. have very low leakage and capacitance when off.

(Of course, that was in about 1990.)

My tube-type GDOs are some of my favorite instruments.

Some of the Keithley electrometers used a special electrometer tube.
Mine uses an early vintage mosfet.

I have one of each: a 405 and a 610C like yours. The 405 works on the
100-fA scale if you let it warm up for an hour or so.

https://www.dropbox.com/s/lo8xsx2x07b4zy4/Welwyn_1G_Keithley.jpg?raw=1

When I first played with mosfets I built a voltage follower and
accidentally left the gate open. The source voltage froze and didn\'t
change a bit. I was amazed. Now one can do cool things with a 2N7000.

If you can find one that isn\'t gate-protected, these days. I have a
reel of 2N7002E\'s because NXP discontinued them.


My 610 doesn\'t work in fast mode, just goes bonkers. Sometimes a
measurement takes half an hour to settle and I have to walk around my
office holding a ground wire. Does yours work in fast mode?


Generally, but not on the three bottom ranges (10, 30, and 100 fA FS).
The 10 fA scale is apparently just there to decorate the front
panel--it\'s too unstable to be useful even in slow mode.

Possibly hooking up a LabJack to the analog output and averaging awhile
might fix it, but if I needed to do that I\'d certainly wire up something
dead bug style in a cast-aluminum stomp box instead of using the Keithley.

Sometime in my declining years I might retrofit my old 602, which is
sort of like a more primitive 610C that runs off a zillion dry cells.

I\'d probably pick a 100-pf polystyrene cap out of my drawer, wire it up
as a current integrator with something like an LMC6001 op amp, and
connect it straight to the input. with some very low leakage reset switch.

Then I\'d do a F/V for higher currents, and differentiate the ramp for
lower ones.

Cheers

Phil Hobbs

One way to measure low current is to let it dump into a cap for an
hour or a week, and then measure the voltage on the cap. That will
work to aA\'s.


Seriously? I\'m surprised there\'s no mention of this in any of the
Keighley books. What sort of cap, though?

Polystyrene, polycarb, or some other I forget. Mylar\'s DA would be a
nuisance.

Somebody, maybe they posted here, measured the self-discharge of a
good film cap. He got numbers like a couple per cent per year. And
even that could be mathed out.

1 pA into 1 nF is a millivolt per second. There are 86K seconds in a
day.

 

[John Larkin]

On Sun, 07 May 2023 13:39:20 +0100, Cursitor Doom <cd@notformail.com>
wrote:

On Fri, 5 May 2023 06:04:43 -0700 (PDT), Anthony William Sloman
bill.sloman@ieee.org> wrote:

On Friday, May 5, 2023 at 7:39:05?PM UTC+10, piglet wrote:
On 05/05/2023 7:10 am, Anthony William Sloman wrote:

Not exactly. VR890 seems to be setting up a -9.0V reference for the dual transistor Q886 to sense, and R880,R881 and R882 divide down the -50V rail to produce a matching -9.0V but R883 (to 0V) and R884 to -53V suck out a bit of current through CR883 which complicates the situation.

If that\'s a design, I\'d hate to see an improvisation.

That\'s a really component-rich design. It was probably much-tinkered.

And not well-thought out.

CR883 would normally be reverse biased, it is there to cope with the
remote sense line getting disconnected.

I thought of that after I\'d made my post, which was a bit embarrassing. European circuit design has adopted a number of conventions that make that kind of mistake less likely.

The schematic is not drawn for great clarity but I am not critical of the design. Looks competent me and has interlocks. The use of higher voltage rails as current sources to the diff amps make it look more confusing than it is.

There are couple of PNP transistors used as current sources on the schematic, but they aren\'t drawn in a way that makes this clear.

There is a rule of thumb that says if you can\'t draw your circuit in a way that makes it clear to other people what it is doing, you probably don\'t have a clear idea of it\'s operation yourself, but American circuit diagrams from that period were pretty much uninformly horrible.

Well, I\'ve never seen anything like this before in a linear PSU from a
respected company. It\'s almost as if they were forced to use
transformers with not enough suitable secondary windings. There\'s a
revision date on this board: 1971.

Tek designed and built their own transformers. And CRTs.

Tek\'s schematics ca 1971 were brilliant and beautiful and fun.

https://w140.com/tekwiki/wiki/Tektronix_Cartoons

Imagine a draftsperson at Philips or Siemens or Oxford trying
something like that. Or even HP.

Sloman is a uniformly sour and sad old git. Ignore him.

 

[Anthony William Sloman]

On Monday, May 8, 2023 at 12:41:13 AM UTC+10, John Larkin wrote:

On Sun, 07 May 2023 13:39:20 +0100, Cursitor Doom <c...@notformail.com
wrote:
On Fri, 5 May 2023 06:04:43 -0700 (PDT), Anthony William Sloman
bill....@ieee.org> wrote:

On Friday, May 5, 2023 at 7:39:05?PM UTC+10, piglet wrote:
On 05/05/2023 7:10 am, Anthony William Sloman wrote:

Not exactly. VR890 seems to be setting up a -9.0V reference for the dual transistor Q886 to sense, and R880,R881 and R882 divide down the -50V rail to produce a matching -9.0V but R883 (to 0V) and R884 to -53V suck out a bit of current through CR883 which complicates the situation.

If that\'s a design, I\'d hate to see an improvisation.

That\'s a really component-rich design. It was probably much-tinkered.

And not well-thought out.

CR883 would normally be reverse biased, it is there to cope with the
remote sense line getting disconnected.

I thought of that after I\'d made my post, which was a bit embarrassing. European circuit design has adopted a number of conventions that make that kind of mistake less likely.

The schematic is not drawn for great clarity but I am not critical of the design. Looks competent me and has interlocks. The use of higher voltage rails as current sources to the diff amps make it look more confusing than it is.

There are couple of PNP transistors used as current sources on the schematic, but they aren\'t drawn in a way that makes this clear.

There is a rule of thumb that says if you can\'t draw your circuit in a way that makes it clear to other people what it is doing, you probably don\'t have a clear idea of it\'s operation yourself, but American circuit diagrams from that period were pretty much uninformly horrible.

Well, I\'ve never seen anything like this before in a linear PSU from a
respected company. It\'s almost as if they were forced to use
transformers with not enough suitable secondary windings. There\'s a
revision date on this board: 1971.

Tek designed and built their own transformers. And CRTs.

Tek\'s schematics ca 1971 were brilliant and beautiful and fun.

https://w140.com/tekwiki/wiki/Tektronix_Cartoons

Imagine a draftsperson at Philips or Siemens or Oxford trying something like that. Or even HP.

Oxford Instruments came a bit later. Philips were Dutch and Siemens was German - they took themselves seriously, at least in their documentation.
The Philips brother were nephews of Karl Marx. though he wasn\'t much of an uncle to them.

https://en.wikipedia.org/wiki/Henriette_Pressburg

> Sloman is a uniformly sour and sad old git. Ignore him.

And I don\'t have any enthusiasm for flattering John Larkin. That makes me a very sour git in his book.

Pity he doesn\'t post anything that might deserve positive comment.

--
Bill Sloman, Sydney

 

[Phil Hobbs]

On 2023-05-07 08:43, Cursitor Doom wrote:

On Thu, 04 May 2023 20:54:26 -0700, John Larkin
jlarkin@highlandSNIPMEtechnology.com> wrote:

On Thu, 4 May 2023 22:40:27 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 2023-05-04 20:22, John Larkin wrote:
On Thu, 4 May 2023 12:57:03 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 2023-05-04 12:26, John Larkin wrote:
On Thu, 4 May 2023 10:26:55 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 2023-05-04 08:39, John Larkin wrote:
On Thu, 4 May 2023 00:32:10 -0400, chuck <donnyduck@gmail.com> wrote:

On 02/05/2023 5:53 p.m., John Larkin wrote:
On Tue, 2 May 2023 16:23:53 -0400, chuck <donnyduck@gmail.com> wrote:

On 02/05/2023 2:43 p.m., John Larkin wrote:


The CR things are crystal rectifiers.




Not quite.


CR = CURRENT RECTIFIER

This design intent was to control startup sequence to ensure the highest
voltage source enables the 50V which enables the 15V.

If the HV was slow in rising, some circuit that uses both supply
voltages would see that as a polarity reversal.

For 3 terminal LDO\'s they mitigate this prompting users to add a reverse
diode from input to output so if the higher input voltage goes down
fast, the diode will protect BE junctions from excessive reverse voltage
|Vr| > 5V.

It was a good question that did not deserve snarky responses.

Tony Stewart
EE since 1975

No snark at all. Crystal Rectifier was the initial meaning of CR.

https://www.reddit.com/r/diyelectronics/comments/yl5s28/whats_this_strange_component_designator_cr1/

https://en.wikipedia.org/wiki/Crystal_detector

https://en.wikipedia.org/wiki/Diode

Rad Lab vol 15 is titled \"Crystal Rectifiers.\" Point-contact diode
mixers were one of the three keys to microwave radar, and radar won
WWII.

The diodes in the Tek schematic are not current regulator diodes,
which are actually a form of jfet. I doubt they existed then. I have
not previously heard the term CURRENT RECTIFIER.


John Larkin
EE since 1966


John I guess I started design in Aerospace at the right time in 1975.
and it was probably my draftsman who said it stood for CURRENT RECTIFIER
which a common descriptor. Although I read most of the Mil-Specs and STD
HBBK\'s from our vast library at Bristol Aerospace, I can\'t recall seeing
it there. It was nice to have any test equipment you needed.

Here is the TEK7904 mainframe service manual.
https://w140.com/Tek_7904_OCRed_by_Tabalabs.pdf


I guess you youngsters don\'t remember point-contact rectifiers,
selenium rectifiers, vacuum tube rectifiers, copper oxide rectifiers,
tungar rectifiers, mercury rectifiers, ignitron rectifiers, vibrator
rectifiers, synchronous rectifiers, foxhole (rusty razor blade)
rectifiers, galena rectifiers, or electrolytic rectifiers.

I actually saw a tungar rectifier in operation when I was a kid. In a
gas station.

There were germanium, silicon, and gallium arsenide rectifiers in
WWII. I *don\'t* remember WWII.


I\'m a skosh younger than you, but I\'ve built things with selenium, tube,
point contact, synchronous, and galena rectifiers. I have a couple of
dozen point contact diodes in a Lista cabinet bin (1N34A, 1N38B, and
1N21C).

Your synchronous rectifiers were probably mosfets, but I was thinking
of the motor-driven mechanical contact types.

(Somebody built a DRAM with leaded capacitors on a spinning disk.)

I think that was John D. Atanasoff (of Atanasoff-Berry Computer fame).


One cool device was a DPDT vibrator, sometimes used in car radios. One
set of contacts pushed 12 volts into a transformer primary and the
other set rectified the secondary. Old tube car radios had some
interesting technology. I used to get them free from junkyards.

Yup. As a teenager, I had an old T19 Mk III tank transceiver that
(iirc) had a companion vibrator supply. Interesting gizmo--I never did
get it to work. I remember a weird E1148 VHF superregen oscillator tube
with two caps on it.


(I once needed some vibrators to help parts in tubes slide down
low-slope feeders on a pick-and-place line, for a friend who had an
assembly shop. I found a suitable gadget at Good Vibrations, a
ladies\', umm, accessory store. That was fun.)



Of course the galena was just for fun, and never actually did very much.
The seleniums and tubes were salvaged from old TVs when I was a boy.
(It was a good thing for me that frying seleniums smell so horrible--I
didn\'t realize that the fumes were dangerous.)

There are still things that tubes are unbeatable at. My last tube
circuit used an 811A to control a grid in an electrostatic drift
chamber--it needed to switch some hundreds of volts, and then go
completely away, i.e. have very low leakage and capacitance when off.

(Of course, that was in about 1990.)

My tube-type GDOs are some of my favorite instruments.

Some of the Keithley electrometers used a special electrometer tube.
Mine uses an early vintage mosfet.

I have one of each: a 405 and a 610C like yours. The 405 works on the
100-fA scale if you let it warm up for an hour or so.

https://www.dropbox.com/s/lo8xsx2x07b4zy4/Welwyn_1G_Keithley.jpg?raw=1

When I first played with mosfets I built a voltage follower and
accidentally left the gate open. The source voltage froze and didn\'t
change a bit. I was amazed. Now one can do cool things with a 2N7000.

If you can find one that isn\'t gate-protected, these days. I have a
reel of 2N7002E\'s because NXP discontinued them.


My 610 doesn\'t work in fast mode, just goes bonkers. Sometimes a
measurement takes half an hour to settle and I have to walk around my
office holding a ground wire. Does yours work in fast mode?


Generally, but not on the three bottom ranges (10, 30, and 100 fA FS).
The 10 fA scale is apparently just there to decorate the front
panel--it\'s too unstable to be useful even in slow mode.

Possibly hooking up a LabJack to the analog output and averaging awhile
might fix it, but if I needed to do that I\'d certainly wire up something
dead bug style in a cast-aluminum stomp box instead of using the Keithley.

Sometime in my declining years I might retrofit my old 602, which is
sort of like a more primitive 610C that runs off a zillion dry cells.

I\'d probably pick a 100-pf polystyrene cap out of my drawer, wire it up
as a current integrator with something like an LMC6001 op amp, and
connect it straight to the input. with some very low leakage reset switch.

Then I\'d do a F/V for higher currents, and differentiate the ramp for
lower ones.

Cheers

Phil Hobbs

One way to measure low current is to let it dump into a cap for an
hour or a week, and then measure the voltage on the cap. That will
work to aA\'s.


Seriously? I\'m surprised there\'s no mention of this in any of the
Keighley books.

You need a sufficiently-good readout amp and reset circuit. We talked
about that a bit in the \'femtoampere\' thread just lately.

Cheers

Phil Hobbs

What sort of cap, though?

Polystyrene, polyprop, or (especially) Teflon.


--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

 

[Cursitor Doom]

On Sun, 07 May 2023 07:40:58 -0700, John Larkin
<jlarkin@highlandSNIPMEtechnology.com> wrote:

On Sun, 07 May 2023 13:39:20 +0100, Cursitor Doom <cd@notformail.com
wrote:

On Fri, 5 May 2023 06:04:43 -0700 (PDT), Anthony William Sloman
bill.sloman@ieee.org> wrote:

On Friday, May 5, 2023 at 7:39:05?PM UTC+10, piglet wrote:
On 05/05/2023 7:10 am, Anthony William Sloman wrote:

Not exactly. VR890 seems to be setting up a -9.0V reference for the dual transistor Q886 to sense, and R880,R881 and R882 divide down the -50V rail to produce a matching -9.0V but R883 (to 0V) and R884 to -53V suck out a bit of current through CR883 which complicates the situation.

If that\'s a design, I\'d hate to see an improvisation.

That\'s a really component-rich design. It was probably much-tinkered.

And not well-thought out.

CR883 would normally be reverse biased, it is there to cope with the
remote sense line getting disconnected.

I thought of that after I\'d made my post, which was a bit embarrassing. European circuit design has adopted a number of conventions that make that kind of mistake less likely.

The schematic is not drawn for great clarity but I am not critical of the design. Looks competent me and has interlocks. The use of higher voltage rails as current sources to the diff amps make it look more confusing than it is.

There are couple of PNP transistors used as current sources on the schematic, but they aren\'t drawn in a way that makes this clear.

There is a rule of thumb that says if you can\'t draw your circuit in a way that makes it clear to other people what it is doing, you probably don\'t have a clear idea of it\'s operation yourself, but American circuit diagrams from that period were pretty much uninformly horrible.

Well, I\'ve never seen anything like this before in a linear PSU from a
respected company. It\'s almost as if they were forced to use
transformers with not enough suitable secondary windings. There\'s a
revision date on this board: 1971.

Tek designed and built their own transformers. And CRTs.

\"Okay guys, we have a thousands of these transformers we designed for
the previous series and never used. We need to get rid of \'em on the
7623A, but they don\'t have enough secondary windings. See if you can
come up with an overly complex and convoluted design to overcome this
limitation. The designer who comes up with the most confusing and
tortuous configuration using the most hard-to-find components will get
a raise.\"

Tek\'s schematics ca 1971 were brilliant and beautiful and fun.

https://w140.com/tekwiki/wiki/Tektronix_Cartoons

Imagine a draftsperson at Philips or Siemens or Oxford trying
something like that. Or even HP.

Sloman is a uniformly sour and sad old git. Ignore him.

Bill and I are around the same age. He seems to have lost his sense of
humour over the years. I\'ve clung on to mine as a survival mechanism
to cope with the fucked-up world we live in today. If I ever became
humourless, I\'d be just like Bill. Only nothing like as good at
electronics. ;-)

 

[John Larkin]

On Sun, 7 May 2023 12:38:36 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

On 2023-05-07 08:43, Cursitor Doom wrote:
On Thu, 04 May 2023 20:54:26 -0700, John Larkin
jlarkin@highlandSNIPMEtechnology.com> wrote:

On Thu, 4 May 2023 22:40:27 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 2023-05-04 20:22, John Larkin wrote:
On Thu, 4 May 2023 12:57:03 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 2023-05-04 12:26, John Larkin wrote:
On Thu, 4 May 2023 10:26:55 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 2023-05-04 08:39, John Larkin wrote:
On Thu, 4 May 2023 00:32:10 -0400, chuck <donnyduck@gmail.com> wrote:

On 02/05/2023 5:53 p.m., John Larkin wrote:
On Tue, 2 May 2023 16:23:53 -0400, chuck <donnyduck@gmail.com> wrote:

On 02/05/2023 2:43 p.m., John Larkin wrote:


The CR things are crystal rectifiers.




Not quite.


CR = CURRENT RECTIFIER

This design intent was to control startup sequence to ensure the highest
voltage source enables the 50V which enables the 15V.

If the HV was slow in rising, some circuit that uses both supply
voltages would see that as a polarity reversal.

For 3 terminal LDO\'s they mitigate this prompting users to add a reverse
diode from input to output so if the higher input voltage goes down
fast, the diode will protect BE junctions from excessive reverse voltage
|Vr| > 5V.

It was a good question that did not deserve snarky responses.

Tony Stewart
EE since 1975

No snark at all. Crystal Rectifier was the initial meaning of CR.

https://www.reddit.com/r/diyelectronics/comments/yl5s28/whats_this_strange_component_designator_cr1/

https://en.wikipedia.org/wiki/Crystal_detector

https://en.wikipedia.org/wiki/Diode

Rad Lab vol 15 is titled \"Crystal Rectifiers.\" Point-contact diode
mixers were one of the three keys to microwave radar, and radar won
WWII.

The diodes in the Tek schematic are not current regulator diodes,
which are actually a form of jfet. I doubt they existed then. I have
not previously heard the term CURRENT RECTIFIER.


John Larkin
EE since 1966


John I guess I started design in Aerospace at the right time in 1975.
and it was probably my draftsman who said it stood for CURRENT RECTIFIER
which a common descriptor. Although I read most of the Mil-Specs and STD
HBBK\'s from our vast library at Bristol Aerospace, I can\'t recall seeing
it there. It was nice to have any test equipment you needed.

Here is the TEK7904 mainframe service manual.
https://w140.com/Tek_7904_OCRed_by_Tabalabs.pdf


I guess you youngsters don\'t remember point-contact rectifiers,
selenium rectifiers, vacuum tube rectifiers, copper oxide rectifiers,
tungar rectifiers, mercury rectifiers, ignitron rectifiers, vibrator
rectifiers, synchronous rectifiers, foxhole (rusty razor blade)
rectifiers, galena rectifiers, or electrolytic rectifiers.

I actually saw a tungar rectifier in operation when I was a kid. In a
gas station.

There were germanium, silicon, and gallium arsenide rectifiers in
WWII. I *don\'t* remember WWII.


I\'m a skosh younger than you, but I\'ve built things with selenium, tube,
point contact, synchronous, and galena rectifiers. I have a couple of
dozen point contact diodes in a Lista cabinet bin (1N34A, 1N38B, and
1N21C).

Your synchronous rectifiers were probably mosfets, but I was thinking
of the motor-driven mechanical contact types.

(Somebody built a DRAM with leaded capacitors on a spinning disk.)

I think that was John D. Atanasoff (of Atanasoff-Berry Computer fame).


One cool device was a DPDT vibrator, sometimes used in car radios. One
set of contacts pushed 12 volts into a transformer primary and the
other set rectified the secondary. Old tube car radios had some
interesting technology. I used to get them free from junkyards.

Yup. As a teenager, I had an old T19 Mk III tank transceiver that
(iirc) had a companion vibrator supply. Interesting gizmo--I never did
get it to work. I remember a weird E1148 VHF superregen oscillator tube
with two caps on it.


(I once needed some vibrators to help parts in tubes slide down
low-slope feeders on a pick-and-place line, for a friend who had an
assembly shop. I found a suitable gadget at Good Vibrations, a
ladies\', umm, accessory store. That was fun.)



Of course the galena was just for fun, and never actually did very much.
The seleniums and tubes were salvaged from old TVs when I was a boy.
(It was a good thing for me that frying seleniums smell so horrible--I
didn\'t realize that the fumes were dangerous.)

There are still things that tubes are unbeatable at. My last tube
circuit used an 811A to control a grid in an electrostatic drift
chamber--it needed to switch some hundreds of volts, and then go
completely away, i.e. have very low leakage and capacitance when off.

(Of course, that was in about 1990.)

My tube-type GDOs are some of my favorite instruments.

Some of the Keithley electrometers used a special electrometer tube.
Mine uses an early vintage mosfet.

I have one of each: a 405 and a 610C like yours. The 405 works on the
100-fA scale if you let it warm up for an hour or so.

https://www.dropbox.com/s/lo8xsx2x07b4zy4/Welwyn_1G_Keithley.jpg?raw=1

When I first played with mosfets I built a voltage follower and
accidentally left the gate open. The source voltage froze and didn\'t
change a bit. I was amazed. Now one can do cool things with a 2N7000.

If you can find one that isn\'t gate-protected, these days. I have a
reel of 2N7002E\'s because NXP discontinued them.


My 610 doesn\'t work in fast mode, just goes bonkers. Sometimes a
measurement takes half an hour to settle and I have to walk around my
office holding a ground wire. Does yours work in fast mode?


Generally, but not on the three bottom ranges (10, 30, and 100 fA FS).
The 10 fA scale is apparently just there to decorate the front
panel--it\'s too unstable to be useful even in slow mode.

Possibly hooking up a LabJack to the analog output and averaging awhile
might fix it, but if I needed to do that I\'d certainly wire up something
dead bug style in a cast-aluminum stomp box instead of using the Keithley.

Sometime in my declining years I might retrofit my old 602, which is
sort of like a more primitive 610C that runs off a zillion dry cells.

I\'d probably pick a 100-pf polystyrene cap out of my drawer, wire it up
as a current integrator with something like an LMC6001 op amp, and
connect it straight to the input. with some very low leakage reset switch.

Then I\'d do a F/V for higher currents, and differentiate the ramp for
lower ones.

Cheers

Phil Hobbs

One way to measure low current is to let it dump into a cap for an
hour or a week, and then measure the voltage on the cap. That will
work to aA\'s.


Seriously? I\'m surprised there\'s no mention of this in any of the
Keighley books.

You need a sufficiently-good readout amp and reset circuit. We talked
about that a bit in the \'femtoampere\' thread just lately.

The setup would be a metal box with the parts inside some mechanical
means to connect the readout circuit to the cap. That shouldn\'t be
hard. The readout thing could be grounded or maybe precharged when
it\'s not connected to the cap.

A reed relay might work, but that has hazards. Reeds are nasty.

 

[Anthony William Sloman]

On Monday, May 8, 2023 at 3:12:01 AM UTC+10, Cursitor Doom wrote:

On Sun, 07 May 2023 07:40:58 -0700, John Larkin <jla...@highlandSNIPMEtechnology.com> wrote:
On Sun, 07 May 2023 13:39:20 +0100, Cursitor Doom <c...@notformail.com> wrote:
On Fri, 5 May 2023 06:04:43 -0700 (PDT), Anthony William Sloman <bill.....@ieee.org> wrote:
On Friday, May 5, 2023 at 7:39:05?PM UTC+10, piglet wrote:
On 05/05/2023 7:10 am, Anthony William Sloman wrote:

<snip>

Sloman is a uniformly sour and sad old git. Ignore him.

Bill and I are around the same age. He seems to have lost his sense of humour over the years.

Cursitor Doom prefers not to get the jokes I make at his expense.

> I\'ve clung on to mine as a survival mechanism to cope with the fucked-up world we live in today.

He doesn\'t realise quite how comical his gullible devotion to climate change denial propaganda really is.

> If I ever became humourless, I\'d be just like Bill.

But much dimmer. And since he doesn\'t get my jokes at his expense, I don\'t find his sense of humour all that impressive.

> Only nothing like as good at electronics. ;-)

I know a few people who are at least as good at electronics as I am, but lots more who are merely pretty good.

--
Bill Sloman, Sydney

 

[Anthony William Sloman]

On Monday, May 8, 2023 at 3:12:13 AM UTC+10, John Larkin wrote:

On Sun, 7 May 2023 12:38:36 -0400, Phil Hobbs <pcdhSpamM...@electrooptical.net> wrote:
On 2023-05-07 08:43, Cursitor Doom wrote:
On Thu, 04 May 2023 20:54:26 -0700, John Larkin <jla...@highlandSNIPMEtechnology.com> wrote:
On Thu, 4 May 2023 22:40:27 -0400, Phil Hobbs <pcdhSpamM...@electrooptical.net> wrote:
On 2023-05-04 20:22, John Larkin wrote:
On Thu, 4 May 2023 12:57:03 -0400, Phil Hobbs <pcdhSpamM...@electrooptical.net> wrote:
On 2023-05-04 12:26, John Larkin wrote:
On Thu, 4 May 2023 10:26:55 -0400, Phil Hobbs <pcdhSpamM...@electrooptical.net> wrote:
On 2023-05-04 08:39, John Larkin wrote:
On Thu, 4 May 2023 00:32:10 -0400, chuck <donn...@gmail.com> wrote:
On 02/05/2023 5:53 p.m., John Larkin wrote:
On Tue, 2 May 2023 16:23:53 -0400, chuck <donn...@gmail.com> wrote:
On 02/05/2023 2:43 p.m., John Larkin wrote:

<snip>

> A reed relay might work, but that has hazards. Reeds are nasty.

Not in my experience. Dry reeds do bounce, but that\'s about it .

This Carey Vibrating Reed Electrometer only seems to have been made from 1975 to 1980. We had one in Melbourne when I was a graduate student (1963-1969) so it must have been an earlier model.

https://collection.sciencemuseumgroup.org.uk/objects/co410207/vibrating-reed-electrometer-electrometers

--
Bill Sloman, Sydney

 

[Cursitor Doom]

On Sun, 7 May 2023 11:08:36 -0700 (PDT), Anthony William Sloman
<bill.sloman@ieee.org> wrote:

On Monday, May 8, 2023 at 3:12:01?AM UTC+10, Cursitor Doom wrote:
On Sun, 07 May 2023 07:40:58 -0700, John Larkin <jla...@highlandSNIPMEtechnology.com> wrote:
On Sun, 07 May 2023 13:39:20 +0100, Cursitor Doom <c...@notformail.com> wrote:
On Fri, 5 May 2023 06:04:43 -0700 (PDT), Anthony William Sloman <bill....@ieee.org> wrote:
On Friday, May 5, 2023 at 7:39:05?PM UTC+10, piglet wrote:
On 05/05/2023 7:10 am, Anthony William Sloman wrote:

snip

Sloman is a uniformly sour and sad old git. Ignore him.

Bill and I are around the same age. He seems to have lost his sense of humour over the years.

Cursitor Doom prefers not to get the jokes I make at his expense.

I\'ve clung on to mine as a survival mechanism to cope with the fucked-up world we live in today.

He doesn\'t realise quite how comical his gullible devotion to climate change denial propaganda really is.

If I ever became humourless, I\'d be just like Bill.

But much dimmer. And since he doesn\'t get my jokes at his expense, I don\'t find his sense of humour all that impressive.

Only nothing like as good at electronics. ;-)

I know a few people who are at least as good at electronics as I am, but lots more who are merely pretty good.

I don\'t think you have anything to worry about, Bill. what you lack in
humility you more than make up for in conceit. ;-)

 

[John Larkin]

On Sun, 07 May 2023 18:11:53 +0100, Cursitor Doom <cd@notformail.com>
wrote:

On Sun, 07 May 2023 07:40:58 -0700, John Larkin
jlarkin@highlandSNIPMEtechnology.com> wrote:

On Sun, 07 May 2023 13:39:20 +0100, Cursitor Doom <cd@notformail.com
wrote:

On Fri, 5 May 2023 06:04:43 -0700 (PDT), Anthony William Sloman
bill.sloman@ieee.org> wrote:

On Friday, May 5, 2023 at 7:39:05?PM UTC+10, piglet wrote:
On 05/05/2023 7:10 am, Anthony William Sloman wrote:

Not exactly. VR890 seems to be setting up a -9.0V reference for the dual transistor Q886 to sense, and R880,R881 and R882 divide down the -50V rail to produce a matching -9.0V but R883 (to 0V) and R884 to -53V suck out a bit of current through CR883 which complicates the situation.

If that\'s a design, I\'d hate to see an improvisation.

That\'s a really component-rich design. It was probably much-tinkered.

And not well-thought out.

CR883 would normally be reverse biased, it is there to cope with the
remote sense line getting disconnected.

I thought of that after I\'d made my post, which was a bit embarrassing. European circuit design has adopted a number of conventions that make that kind of mistake less likely.

The schematic is not drawn for great clarity but I am not critical of the design. Looks competent me and has interlocks. The use of higher voltage rails as current sources to the diff amps make it look more confusing than it is.

There are couple of PNP transistors used as current sources on the schematic, but they aren\'t drawn in a way that makes this clear.

There is a rule of thumb that says if you can\'t draw your circuit in a way that makes it clear to other people what it is doing, you probably don\'t have a clear idea of it\'s operation yourself, but American circuit diagrams from that period were pretty much uninformly horrible.

Well, I\'ve never seen anything like this before in a linear PSU from a
respected company. It\'s almost as if they were forced to use
transformers with not enough suitable secondary windings. There\'s a
revision date on this board: 1971.

Tek designed and built their own transformers. And CRTs.

\"Okay guys, we have a thousands of these transformers we designed for
the previous series and never used. We need to get rid of \'em on the
7623A, but they don\'t have enough secondary windings. See if you can
come up with an overly complex and convoluted design to overcome this
limitation. The designer who comes up with the most confusing and
tortuous configuration using the most hard-to-find components will get
a raise.\"

I charitably assume that\'s an actual quote from a Tek engineer, and
that you didn\'t make that up.

Did you ever work with any ex-Tek engineeers? I have worked with two.

Tek\'s schematics ca 1971 were brilliant and beautiful and fun.

https://w140.com/tekwiki/wiki/Tektronix_Cartoons

Imagine a draftsperson at Philips or Siemens or Oxford trying
something like that. Or even HP.

Sloman is a uniformly sour and sad old git. Ignore him.

Bill and I are around the same age. He seems to have lost his sense of
humour over the years. I\'ve clung on to mine as a survival mechanism
to cope with the fucked-up world we live in today.

The world is a pretty good place and by most indications keeps getting
better.

 

[piglet]

On 07/05/2023 13:39, Cursitor Doom wrote:

Well, I\'ve never seen anything like this before in a linear PSU from a
respected company. It\'s almost as if they were forced to use
transformers with not enough suitable secondary windings. There\'s a
revision date on this board: 1971.

Not sure I understand why you think there aren\'t enough secondary
windings? There is one for -/+50, one for -/+15 one for +5 and one for
80-90 which added to +50 made 130V. Seems like plenty, how would more
windings make it simpler? The 130V regulation occurring at 50V is
economical, other HV supplies of that era used that trick too.

piglet



Here is the service manual extract...

LOW-VOLTAGE POWER SUPPLY
The Low-Voltage Power Supply circuit provides the
operating power for this instrument from six regulated
supplies. Electronic regulation is used to provide stable,
low-ripple output voltages. Each supply (except the -i 130 V
supply, which is fused) contains a short-protection circuit
to prevent instrument damage if a supply is inadvertently
over-loaded or shorted to ground. Fig. 3-22 shows a
detailed block diagram of the Low-Voltage Power Supply
circuit. A schematic of this circuit is shown on diagram 8 at the rear
of this manual.

Power Input
Power is applied to the primary of transformer T801
through line fuse F1000, thermal cutout S1000, and
POWER switch S1001. The Voltage-Selector Jumper,
P1001, connects the two halves of the primary of T801 in
parallel for 110-volt (nominal) operation. Voltage-Selector
Jumper P1002 connects the two halves of the primary in
series for 220-volt (nominal) operation. The line fuse,
F1000, must be changed to provide the correct protection
for 220-volt nominal operation.

Each half of the primary of T801 has taps above and
below the 110-volt (220-volt) nominal point. When the
Voltage Selector Jumper is moved from LOW to MED to
HI, more turns are effectively added to the primary winding
and the turns ratio is decreased to compensate for the
increased primary voltage. This configuration extends the
regulating range of the 7623.

For the R7623, a fan provides forced-air cooling. The
fan is connected in parallel with one half of the primary
winding of T801. Therefore, it always has the same voltage
applied regardless of the position of the Voltage-Selector
Jumper.

Thermal cutout S1000 provides thermal protection for
this instrument. If the internal temperature of the instrument exceeds a
safe operating level, S1000 opens to
interrupt the applied power. When the temperature returns
to a safe level, S1000 automatically closes to re-apply the
power.

-50-Volt Supply
The following discussion includes the description of the
50 V Rectifier, 50 V Series Regulator, -50 V Feedback
Amplifier, - 50 V Reference, and -50 V Current Limiting
stages. Since these stages are closely related in the operation
of the -50-volt regulated output, their performance is most
easily understood when discussed as a unit.

The 50 V Rectifier assembly CR808 rectifies the output
at the secondary of T801 to provide the unregulated
voltage source for both the —50- and +50-volt supplies.
CR808 is connected as a bridge rectifier and its output is
filtered by C808-C809. Transistors Q886, Q896, Q900
operate as a feedback-stabilized regulator circuit to maintain a
constant -50 volt output level. Q886 is connected as
a differential amplifier to compare the feedback voltage at
the base of Q886B against the reference voltage at the base
of Q886A. The error output at the collector of Q886B
reflects the difference, if any, between these two inputs.
The change in error-output level at the collector of Q886B
is always opposite in direction to the change in the
feedback input at the base of Q886B (out of phase).

Zener diode VR890 sets a reference level of about —9
volts at the base of Q886A. A feedback sample of the
output voltage from this supply is connected to the base of
Q886B through divider R880-R881-R882. R881 in this
divider is adjustable to set the output level of this supply.
Notice that the feedback voltage to this divider is obtained
from a line labeled -50 V Sense. Fig. 3-23 illustrates the
reason for this configuration. The inherent resistance of the
interconnecting wire between the output of the -50-Volt
Supply and the load produces a voltage drop which is equal
to the output current multiplied by the resistance of the
interconnecting wire. Even though the resistance of the
wire is small, it results in a substantial voltage drop due to
the high output current of this supply. Therefore, if the
feedback voltage were obtained ahead of this drop, the
voltage at the load might not maintain close regulation.
However, the -50 V Sense feedback configuration overcomes this problem
since it obtains the feedback voltage
from a point as close as practical to the load. Since the
current in the —50 V Sense line is small and constant, the
feedback voltage is an accurate sample of the voltage
applied to the load.

Regulation occurs as follows: If the output level of this
supply decreases (less negative) due to an increase in load,
or a decrease in input voltage (as a result of line voltage
changes or ripple), the voltage across divider R880-
R881-R882 decreases also. This results in a more positive
feedback level at the base of Q886B than that established
by the —50 V Reference stage at the base of Q886A. Since
the transistor with the more positive base controls the
conduction of the differential amplifier, the output current
at the collector of Q886B increases. This increase in output
from Q886B allows more current to flow through Q896
and Q900 to result in increased conduction of - 50 V Series
Regulator Q903. The load current increases and the output
voltage of this supply also increases (more negative). As a
result, the feedback voltage from the —50 V Sense line
increases and the base of Q8868 returns to the same level as
the base of Q886A. Similarly, if the output level of this
supply increases (more negative), the output current of
Q886B decreases. The feedback through Q896 and Q900
reduces the conduction of the -50 V Series Regulator to
decrease the output voltage of this supply.



—50 Volts adjustment R881 determines the divider ratio
to the base of Q886B and thereby determines the feedback
voltage. This adjustment sets the output level of the supply
in the following manner: If R881 is adjusted so the voltage
at its variable arm goes less negative (closer to ground), this
appears as an error signal at the base of Q886B. In the same
manner as described previously, this positive-going change
at the feedback input of the differential amplifier increases
the conduction of the -50 V Series Regulator to produce
more current to the load, and thereby increase the output
voltage of this supply. This places more voltage across
divider R880-R881-R882 and the divider action returns the
base of Q886B to about - 9 volts. Notice that the feedback
action of this supply forces a change in the output level
which always returns the base of Q886B to the same level
as the base of Q886A. In this manner, the output level of
the —50-Volt Supply can be set to exactly —50 volts by
correct adjustment of R881.

The —50 V Current Limiting stage Q908-Q909 Q910
protects the - 50-Volt Supply if excess current is demanded
from this supply. All of the output current from the
—50 Volt Supply flows through R903. Transistor Q908
senses the voltage at the collector of the -50 V Series
Regulator Q903 and compares it against the -50 V output
level at the base of Q909 which is obtained from the other
side of R903. Under normal operation, Q908 is held in
conduction and Q909 is off. However, when excess current
is demanded from the -50 V Series Regulator due to a
short circuit or similar malfunction at the output of this
supply, the voltage drop across R903 increases until the
base of 0908 goes more negative than the level at the base
of Q909. Then Q909 takes over conduction of the
comparator. The collector current of Q909 increases the
voltage drop across R896 to reduce the conduction of
Q896 in the —50 V Feedback Amplifier and limit the
conduction of Q903. Q910 is connected as a constantcurrent source for
Q908-Q909.

—15-Volt Supply
Basic operation of all stages in the —15-V Supply is the
same as for the —50-Volt Supply. Reference level for this
supply is established by divider R945-R946 between
ground and the —50 V Sense voltage. The divider ratio of
R945-R946 sets a level of -15 volts at the base of Q943A.
The level on the 50 V Sense line is held stable by the
-50-Volt Supply as described previously. The -15 V Sense
voltage is connected to the base of Q943B through R940.
Any change at the output of the —15-Volt Supply appears
at the base of Q943B as an error signal. The output voltage
is regulated in the same manner as described for the
-50-Volt Supply.



+5-Volt Supply
Basic operation of the +5-Volt Supply is the same as
described for the previous supplies. The +5 V Current
Limiting and +5 V Feedback Amplifier (except for Q985) is
made up of a five-transistor array U973. Notice that both
U973C and Q985 in the +5 V Feedback Amplifier are
connected as emitter followers, since inversion is not
necessary in the feedback path for positive output voltages.
Reference voltage for the +5 V Feedback Amplifier stage is
established by divider R970-R971 between the +5 V Sense
and - 50 V Sense feedback voltages. This divider establishes
a quiescent level of about 0 volt at the base of U973E.


+ 15-Volt Supply

The + 15-Volt Supply operates in the same manner as
described for the previous supplies. The unregulated
+ 15 Volt Supply provides the source voltage for the
High-Voltage Oscillator stage in the CRT circuit through
fuse F814 and P870.

+50-Volt Supply
Operation of the +50-Volt Supply is the same as
described for the previous supplies. The unregulated +50
volts, from 50 V Rectifier CR808, is used to provide a
positive starting voltage for the -50-Volt Supply.

+ 130-Volt Supply
The + 130-V Rectifier CR806 provides the rectified
voltage for the + 130-Volt Supply. However, this secondary
winding of T801 does not supply the full potential
necessary to obtain the +130-volt output level. To provide
the required output level, the +50-Volt Supply is connected
in series with this supply through Q850. Basic regulation of
the output voltage is provided by +130 V Feedback
Amplifier Q852, and +130 V Series Regulator Q850.

The output voltage of this supply is connected across
divider R855 R856. This divider provides a quiescent level
of about +50 volts at the base of Q852. The reference level
for this supply is provided by the +50-Volt Supply
connected to the emitter of Q852. If the output of this
supply changes, this change is sensed by Q852 and an
amplified error signal is connected to the base of Q850.
This error signal changes the conduction of the +130 V
Series Regulator Q850 to correct the output error. Fuse
F855 protects this supply if the output is shorted.
However, since the response time of F855 is slow to a
shorted condition, VR851 provides additional current to
the base of Q850 to protect it from damage due to over
voltage. Diode CR852 limits the reverse bias on Q852 to
about 0.6 volt when F855 is blown.


Graticule Light Supply
Power for the graticule lights is supplied by the Graticule
Light Supply. Rectified voltage for this supply is provided
by 5 V Rectifier CR820-CR821. Q835 operates as a series
regulator transistor. Emitter follower Q829 determines the
conduction of this series regulator as controlled by front
panel GRATICULE ILLUM Control R1095. Currentlimiting to protect this
supply is provided by Q827. Under
normal operation, divider R830-R831-R833 sets the base of
0827 below its conduction level. However, if excess current
is demanded from this supply, the voltage drop across
R837-R838 increases until Q827 comes into conduction.
The collector of Q827 then limits the conduction of this
supply to limit its output current.

Divider R822 R823 provides a sample of the line voltage
in the secondary of T801 to the plug-in unit. This provides
a line-frequency reference to the plug-in units for internal
triggering at line frequency or for other applications.

 

[piglet]

On 06/05/2023 00:11, John Larkin wrote:

On Fri, 5 May 2023 19:48:14 +0100, piglet <erichpwagner@hotmail.com
wrote:

Q835
et al are the graticule lamps dimmer.

Was that an old scope with an external edge-lit plastic graticule? Or
the later internal one?

Sorry no idea.

piglet

 

[Cursitor Doom]

On Sun, 7 May 2023 22:39:43 +0100, piglet <erichpwagner@hotmail.com>
wrote:

On 06/05/2023 00:11, John Larkin wrote:
On Fri, 5 May 2023 19:48:14 +0100, piglet <erichpwagner@hotmail.com
wrote:

Q835
et al are the graticule lamps dimmer.

Was that an old scope with an external edge-lit plastic graticule? Or
the later internal one?




Sorry no idea.

piglet

External.