Developing HV DC Pulses...

[John Larkin]

On Thu, 11 May 2023 16:14:54 -0700 (PDT), Lamont Cranston
<amdx62@gmail.com> wrote:

On Thursday, May 11, 2023 at 6:00:46?PM UTC-5, whit3rd wrote:
On Thursday, May 11, 2023 at 12:59:11?PM UTC-7, Lamont Cranston wrote:
On Thursday, May 11, 2023 at 1:08:38?PM UTC-5, John Larkin wrote:

Driving the grid positive would turn it on harder.
Got it, but, the tube curves show up to 7 V negative to pinch it off.
Do I need a ± supply to switch it on and off hard.
Don\'t see why; your current is a milliamp (or less), so simply driving grid and cathode in opposite
senses will give you +12 to -12 off of a single +12 power source.

I\'m getting info that you don\'t want the grid to go positive, just to 0V and negative a few volts, in relation to the cathode.
As I understand it, with the grid at 0V the tube has no current flow, as the grid voltage goes more negative
current starts to flow until it is turned all the on. Is that correct?
Also, what is the voltage drop across a tube in full conduction?
Does it get pretty close to 0V, or 10V or 100V?
Mikek

Positive on the grid would help drive the plate closer to ground.

Look at the 6BK4 transfer curves. Plate current is increasing hard as
grid voltage is increasing past 0 volts. We are literally in uncharted
territory.

 

[Lamont Cranston]

On Thursday, May 11, 2023 at 7:36:56 PM UTC-5, John Larkin wrote:

Positive on the grid would help drive the plate closer to ground.

Look at the 6BK4 transfer curves. Plate current is increasing hard as
grid voltage is increasing past 0 volts. We are literally in uncharted
territory.

The curve doesn\'t show grid voltage increasing past 0 Volts.
But I can now see, if I use the 20,000 volt line,
with -12V on the grid 0 ma of currents flows.
with -10V on the grid 0.06 ma of currents flows.
with -8V on he grid 0.375 ma of currents flows.
with -5 on the grid 1.35 ma of currents flows.
with -3V on the grid 2 ma of currents flows.

So as the grid voltage goes less negative (positive direction) more current flows.
Thanks, Mikek
P.S. Tube, socket, 2N7000s, some 2W, 1.5MΩ High Voltage resistors ordered.
Resistors are for voltage divider to my used with a multi voltage experiment.

 

[John Larkin]

On Thu, 11 May 2023 18:00:42 -0700 (PDT), Lamont Cranston
<amdx62@gmail.com> wrote:

On Thursday, May 11, 2023 at 7:36:56?PM UTC-5, John Larkin wrote:

Positive on the grid would help drive the plate closer to ground.

Look at the 6BK4 transfer curves. Plate current is increasing hard as
grid voltage is increasing past 0 volts. We are literally in uncharted
territory.

The curve doesn\'t show grid voltage increasing past 0 Volts.

They stopped graphing, but the slope is steep at 0 volts. It ain\'t
going to flatten out at +1.

Positive on the grid will accelerate electrons towards the plate. And
draw a little grid current.

But I can now see, if I use the 20,000 volt line,
with -12V on the grid 0 ma of currents flows.
with -10V on the grid 0.06 ma of currents flows.
with -8V on he grid 0.375 ma of currents flows.
with -5 on the grid 1.35 ma of currents flows.
with -3V on the grid 2 ma of currents flows.

What you really need is lines for +1000 and +250 on the plate, but the
people who designed this tube never expected it to be used as a
saturating switch.

It would be interesting to test it as a switch with positive grid
voltage. I guess you will!

So as the grid voltage goes less negative (positive direction) more current flows.
Thanks, Mikek
P.S. Tube, socket, 2N7000s, some 2W, 1.5M? High Voltage resistors ordered.
Resistors are for voltage divider to my used with a multi voltage experiment.

 

[whit3rd]

On Thursday, May 11, 2023 at 7:45:22 AM UTC-7, John Larkin wrote:

On Wed, 10 May 2023 23:26:36 -0700 (PDT), whit3rd <whi...@gmail.com
wrote:
On Wednesday, May 10, 2023 at 5:06:03?PM UTC-7, John Larkin wrote:
On Wed, 10 May 2023 14:38:05 -0700 (PDT), whit3rd <whi...@gmail.com
wrote:

And, a \"HV resistor\" is geometrically designed to not generate ions in air;
regular old air is NOT a good insulator at high fields...
A 1-cent axial isn\'t fat enough to do real HV, unless you put it in a
vacuum, or pot the assembly.

I suggested using several in series. That works fine.

It isn\'t end-to-end arcing that\'s the issue, but local E field causing corona
discharge (and chemical corrosion that can kill nearby components in a few months).
Diameter, not heating, is the critical bit.

I was building 12 KV supplies when I was a kid, and I used strings of
series 1/4 watt carbon axial resistors, and they worked fine. A 1B3
makes a great series regulator.

Composition resistors ARE rather fat, compared to metal-film traces on a ceramic base.
To see corona discharge, did you examine your 12kV supplies in the dark?
That\'s how you check for corona: I\'ve noticed it in seventies-vintage car
ignition wiring (glows real pretty, time to buy aftermarket silicone wires)..

> I am sure glad that you don\'t design electronics.

I\'m relieved you\'re not teaching electronics. I\'ve had quite a few CRT focus resistors
fail, enough to diagnose (and fix) the sister\'s TV from seeing the familiar symptoms. That\'s only a 4kV
component, usually, and the failure is from corona. Early decay of the component,
not immediate failure that a kid would notice.

 

[Phil Hobbs]

John Larkin <jlarkin@highlandSNIPMEtechnology.com> wrote:

On Thu, 11 May 2023 18:00:42 -0700 (PDT), Lamont Cranston
amdx62@gmail.com> wrote:

On Thursday, May 11, 2023 at 7:36:56?PM UTC-5, John Larkin wrote:

Positive on the grid would help drive the plate closer to ground.

Look at the 6BK4 transfer curves. Plate current is increasing hard as
grid voltage is increasing past 0 volts. We are literally in uncharted
territory.

The curve doesn\'t show grid voltage increasing past 0 Volts.

They stopped graphing, but the slope is steep at 0 volts. It ain\'t
going to flatten out at +1.

Positive on the grid will accelerate electrons towards the plate. And
draw a little grid current.

But I can now see, if I use the 20,000 volt line,
with -12V on the grid 0 ma of currents flows.
with -10V on the grid 0.06 ma of currents flows.
with -8V on he grid 0.375 ma of currents flows.
with -5 on the grid 1.35 ma of currents flows.
with -3V on the grid 2 ma of currents flows.

What you really need is lines for +1000 and +250 on the plate, but the
people who designed this tube never expected it to be used as a
saturating switch.

It would be interesting to test it as a switch with positive grid
voltage. I guess you will!



So as the grid voltage goes less negative (positive direction) more current flows.
Thanks, Mikek
P.S. Tube, socket, 2N7000s, some 2W, 1.5M? High Voltage resistors ordered.
Resistors are for voltage divider to my used with a multi voltage experiment.

One reason for the choice of graph limits is to protect the tube. Grid
heating isn’t an issue at +1 V_g-k, but cathode damage may be.

Cheers

Phil Hobbs

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

 

[Lamont Cranston]

On Friday, May 12, 2023 at 4:32:33 AM UTC-5, whit3rd wrote:
That\'s only a 4kV

component, usually, and the failure is from corona. Early decay of the component,
not immediate failure that a kid would notice.

I\'ll keep that in component decay in mind, but these are short tests of 15 minutes at most, all in open air.
If this every becomes part of useful system, it will be long past me helping my son do tests,
and the design will being someone else\'s hands.
That\'s a good idea, turning out the lights to see corona. Seeing where it is, gives us a chance to reduce it.

Last night I set up the transformer for halfwave output. I have two 8kV diodes in series in case we go over 8kV.
I monitored the output with my scope, expecting to see a halfwave waveform. I didn\'t, as I raised the variac voltage,
the scope show a distorted waveform with small halfwave peaks. but over a second or two it diminished to 0.
Another bump up on the variac and you could see the distorted wave form again, but it diminished to 0.
I finally put a 2.5MΩ load on it and then waveform looked normal halfwave waveform.
Then I put only an 18pf on it to simulate the actual load. This brought the waveform back to the distorted waveform situation.
The obvious solution is to add a resistive load in parallel with the vessel.
But, I\'m curious, is this some characteristic of the HV diodes that is causing this?
I.e, the HV diodes need a certain amount of current to work properly.

Thanks, Mikek

 

[Lamont Cranston]

I\'m wondering if the tube solution is going to leave a +150V to +7kV pulse, i.e. won\'t go to 0V?
I don\'t know if 150V will cause enough electric field to have control over water droplets,
but I would like to get as close to 0V a possible. I think part of why pulse may be better in
oil/water separation is because of the rest time allowing coalescence of he water bubbles,
but that is just my speculation.
Mikek

Mikek

 

[John Larkin]

On Fri, 12 May 2023 11:30:39 -0000 (UTC), Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

John Larkin <jlarkin@highlandSNIPMEtechnology.com> wrote:
On Thu, 11 May 2023 18:00:42 -0700 (PDT), Lamont Cranston
amdx62@gmail.com> wrote:

On Thursday, May 11, 2023 at 7:36:56?PM UTC-5, John Larkin wrote:

Positive on the grid would help drive the plate closer to ground.

Look at the 6BK4 transfer curves. Plate current is increasing hard as
grid voltage is increasing past 0 volts. We are literally in uncharted
territory.

The curve doesn\'t show grid voltage increasing past 0 Volts.

They stopped graphing, but the slope is steep at 0 volts. It ain\'t
going to flatten out at +1.

Positive on the grid will accelerate electrons towards the plate. And
draw a little grid current.

But I can now see, if I use the 20,000 volt line,
with -12V on the grid 0 ma of currents flows.
with -10V on the grid 0.06 ma of currents flows.
with -8V on he grid 0.375 ma of currents flows.
with -5 on the grid 1.35 ma of currents flows.
with -3V on the grid 2 ma of currents flows.

What you really need is lines for +1000 and +250 on the plate, but the
people who designed this tube never expected it to be used as a
saturating switch.

It would be interesting to test it as a switch with positive grid
voltage. I guess you will!



So as the grid voltage goes less negative (positive direction) more current flows.
Thanks, Mikek
P.S. Tube, socket, 2N7000s, some 2W, 1.5M? High Voltage resistors ordered.
Resistors are for voltage divider to my used with a multi voltage experiment.


One reason for the choice of graph limits is to protect the tube. Grid
heating isn’t an issue at +1 V_g-k, but cathode damage may be.

Cheers

Phil Hobbs

There is very little to be googled about using tubes with positive
grid voltage. Most people just ignore the possibility, or say DONT DO
IT.

I did find an interesting study on the subject. It\'s from 1933 and
it\'s still paywalled after 90 years.

But I do still have the 1964 edition of the RCA Transmitting Tube
manual, nice bedtime reading. Driving big transmit jugs with positive
grid voltage is the way to get RF power. Some data sheets have curves
that don\'t show anything below zero but go to +300 on the grid. The
current enhancement, as compared to Idss, gets up into the 20:1 and
even 50:1 range.

Based on these curves, I wild-guess that my imagined circuit could
enhance a wimpy 6BK4 by something like 2:1 or maybe 5:1, which it
probably needs.

 

[John Larkin]

On Fri, 12 May 2023 05:33:48 -0700 (PDT), Lamont Cranston
<amdx62@gmail.com> wrote:

I\'m wondering if the tube solution is going to leave a +150V to +7kV pulse, i.e. won\'t go to 0V?
I don\'t know if 150V will cause enough electric field to have control over water droplets,
but I would like to get as close to 0V a possible. I think part of why pulse may be better in
oil/water separation is because of the rest time allowing coalescence of he water bubbles,
but that is just my speculation.
Mikek

Mikek

A tube will certainly not swing to ground. One might be lucky to get a
6BK4 to go down to 500. But as I understand it, the sample is in a
glass centrifuge tube, so the system is inherently AC-coupled and all
you need is peak-to-peak pulse voltage.

 

[Anthony William Sloman]

On Friday, May 12, 2023 at 7:05:47 AM UTC+10, John Larkin wrote:

On Thu, 11 May 2023 12:59:07 -0700 (PDT), Lamont Cranston
amd...@gmail.com> wrote:
On Thursday, May 11, 2023 at 1:08:38?PM UTC-5, John Larkin wrote:

Driving the grid positive would turn it on harder.

Got it, but, the tube curves show up to 7 V negative to pinch it off.
Do I need a ą supply to switch it on and off hard.

No, there is a simple, elegant circuit that needs just one small power
supply, plus the HV of course.

Sloman says that I am a hack who can only make minor tweaks to my own circuits (which is an interesting bit of logic itself) so I think he should contribute the first schematic.

My assumption is that John Larkin starts off with circuits that he gets from other people, and tweaks them until he gets a result he thinks he can sell, at which point they become \"his circuits\".

Of course John thinks that somebody else should contribute the first schematic - he should have had time to work out that Mikek hasn\'t actually specified his problem in a way that would let anybody design anything from scratch.

Neon sign transformers do seem to be part of the kind of solution that Mikek has on mind, and without a fairly detailed specification of the particular neon sign transformers he\'s planning on using, working out a detailed schematic that might work is pretty difficult. If John actually designed his circuits he\'d know about that.

> Of course, he won\'t use any of my dumb suggestions.

I\'ve tried to make helpful suggestions. So has John. What\'s fairly clear is that is isn\'t so much a design problem as a case of improvising around what Mikeke and his son have to hand - and Mikek hasn\'t posted any kind of detailed list.

> (I haven\'t used tubes since I was a kid. A 6BK4 actually makes sense here. No mosfet is going to have 27 KV Vd-s or 1 pF drain capacitance.)

Mikek doesn\'t want 27 kV, and he\'s trying to set setting up 10msec or wider high voltage pulses. Drain capacitance isn\'t an issue. Valves/tubes do have advantages in specialised jobs, but they tend be bulky and fragile and keeping the electron-emitting filament warm is always a pain. MOSFETs should work fine, though perhaps not with neon sign transformers.

Mikek\'s experiments with his neon sign transfomer produce strange results - the fact that he has to load the output with 2.5M of resistance before he can see a half wave suggests that there are capacitors embedded in his set-up. The fact that 18pF killed it off again says that it might just be the interwinding capacitance in the transformer - easy enough to measure if you know what you are doing.

--
Bill Sloman, Sydney

 

[Phil Hobbs]

On 2023-05-12 10:09, John Larkin wrote:

On Fri, 12 May 2023 11:30:39 -0000 (UTC), Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

John Larkin <jlarkin@highlandSNIPMEtechnology.com> wrote:
On Thu, 11 May 2023 18:00:42 -0700 (PDT), Lamont Cranston
amdx62@gmail.com> wrote:

On Thursday, May 11, 2023 at 7:36:56?PM UTC-5, John Larkin wrote:

Positive on the grid would help drive the plate closer to ground.

Look at the 6BK4 transfer curves. Plate current is increasing hard as
grid voltage is increasing past 0 volts. We are literally in uncharted
territory.

The curve doesn\'t show grid voltage increasing past 0 Volts.

They stopped graphing, but the slope is steep at 0 volts. It ain\'t
going to flatten out at +1.

Positive on the grid will accelerate electrons towards the plate. And
draw a little grid current.

But I can now see, if I use the 20,000 volt line,
with -12V on the grid 0 ma of currents flows.
with -10V on the grid 0.06 ma of currents flows.
with -8V on he grid 0.375 ma of currents flows.
with -5 on the grid 1.35 ma of currents flows.
with -3V on the grid 2 ma of currents flows.

What you really need is lines for +1000 and +250 on the plate, but the
people who designed this tube never expected it to be used as a
saturating switch.

It would be interesting to test it as a switch with positive grid
voltage. I guess you will!



So as the grid voltage goes less negative (positive direction) more current flows.
Thanks, Mikek
P.S. Tube, socket, 2N7000s, some 2W, 1.5M? High Voltage resistors ordered.
Resistors are for voltage divider to my used with a multi voltage experiment.


One reason for the choice of graph limits is to protect the tube. Grid
heating isn’t an issue at +1 V_g-k, but cathode damage may be.

Cheers

Phil Hobbs

There is very little to be googled about using tubes with positive
grid voltage. Most people just ignore the possibility, or say DONT DO
IT.

I did find an interesting study on the subject. It\'s from 1933 and
it\'s still paywalled after 90 years.

But I do still have the 1964 edition of the RCA Transmitting Tube
manual, nice bedtime reading. Driving big transmit jugs with positive
grid voltage is the way to get RF power. Some data sheets have curves
that don\'t show anything below zero but go to +300 on the grid. The
current enhancement, as compared to Idss, gets up into the 20:1 and
even 50:1 range.

Based on these curves, I wild-guess that my imagined circuit could
enhance a wimpy 6BK4 by something like 2:1 or maybe 5:1, which it
probably needs.

Big transmitting tubes usually have directly-heated tungsten cathodes,
which are bulletproof but have low emission at a given temperature.

Oxide cathodes are much stronger emitters, but are far more delicate.
Some are designed to run at full emission, e.g. in your 5U4 rectifier.

Most receiving tubes can be permanently damaged by pulling too much
cathode current. See e.g. Wegener, \"The Oxide-Coated Cathode\"

https://electrooptical.net/OldBooks/OxideCoatedCathodV1.djvu
https://electrooptical.net/OldBooks/OxideCoatedCathodeVol2.djvu

Cheers

Phil Hobbs

--
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

 

[John Larkin]

On Fri, 12 May 2023 13:33:29 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

On 2023-05-12 10:09, John Larkin wrote:
On Fri, 12 May 2023 11:30:39 -0000 (UTC), Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

John Larkin <jlarkin@highlandSNIPMEtechnology.com> wrote:
On Thu, 11 May 2023 18:00:42 -0700 (PDT), Lamont Cranston
amdx62@gmail.com> wrote:

On Thursday, May 11, 2023 at 7:36:56?PM UTC-5, John Larkin wrote:

Positive on the grid would help drive the plate closer to ground.

Look at the 6BK4 transfer curves. Plate current is increasing hard as
grid voltage is increasing past 0 volts. We are literally in uncharted
territory.

The curve doesn\'t show grid voltage increasing past 0 Volts.

They stopped graphing, but the slope is steep at 0 volts. It ain\'t
going to flatten out at +1.

Positive on the grid will accelerate electrons towards the plate. And
draw a little grid current.

But I can now see, if I use the 20,000 volt line,
with -12V on the grid 0 ma of currents flows.
with -10V on the grid 0.06 ma of currents flows.
with -8V on he grid 0.375 ma of currents flows.
with -5 on the grid 1.35 ma of currents flows.
with -3V on the grid 2 ma of currents flows.

What you really need is lines for +1000 and +250 on the plate, but the
people who designed this tube never expected it to be used as a
saturating switch.

It would be interesting to test it as a switch with positive grid
voltage. I guess you will!



So as the grid voltage goes less negative (positive direction) more current flows.
Thanks, Mikek
P.S. Tube, socket, 2N7000s, some 2W, 1.5M? High Voltage resistors ordered.
Resistors are for voltage divider to my used with a multi voltage experiment.


One reason for the choice of graph limits is to protect the tube. Grid
heating isn’t an issue at +1 V_g-k, but cathode damage may be.

Cheers

Phil Hobbs

There is very little to be googled about using tubes with positive
grid voltage. Most people just ignore the possibility, or say DONT DO
IT.

I did find an interesting study on the subject. It\'s from 1933 and
it\'s still paywalled after 90 years.

But I do still have the 1964 edition of the RCA Transmitting Tube
manual, nice bedtime reading. Driving big transmit jugs with positive
grid voltage is the way to get RF power. Some data sheets have curves
that don\'t show anything below zero but go to +300 on the grid. The
current enhancement, as compared to Idss, gets up into the 20:1 and
even 50:1 range.

Based on these curves, I wild-guess that my imagined circuit could
enhance a wimpy 6BK4 by something like 2:1 or maybe 5:1, which it
probably needs.


Big transmitting tubes usually have directly-heated tungsten cathodes,
which are bulletproof but have low emission at a given temperature.

Oxide cathodes are much stronger emitters, but are far more delicate.
Some are designed to run at full emission, e.g. in your 5U4 rectifier.

Most receiving tubes can be permanently damaged by pulling too much
cathode current. See e.g. Wegener, \"The Oxide-Coated Cathode\"

https://electrooptical.net/OldBooks/OxideCoatedCathodV1.djvu
https://electrooptical.net/OldBooks/OxideCoatedCathodeVol2.djvu

Cheers

Phil Hobbs

We\'d expect maybe a few mA peak cathode current, and that might be at
a 10% duty cycle, and this is a science project. It would probably be
OK.

The plate current would be under 1 mA when ON. I have no idea what the
grid current might be with a modest positive grid bias.

Screen grids run positive, typically at a few mA.

 

[Lamont Cranston]

On Friday, May 12, 2023 at 9:42:37 AM UTC-5, Anthony William Sloman wrote:

Mikek\'s experiments with his neon sign transfomer produce strange results - the fact that he has to load the output with 2.5M of resistance before he can see a half wave suggests that there are capacitors embedded in his set-up. The fact that 18pF killed it off again says that it might just be the interwinding capacitance in the transformer - easy enough to measure if you know what you are doing.

--
Bill Sloman, Sydney

I don\'t doubt there is a large self capacitance in the secondary,
there are lots of turns.
Well, I thought I knew what I was doing, I used C1-4C2 / 3.
But C1 = 3,208pf @ 75Hz and C2 = 945pf @ 150Hz.
3208 - (4x 945) / 3 = 3208 -3780 / 3
That doesn\'t compute, I did it twice and got very similar results.
Any help?

 

[Lamont Cranston]

On Friday, May 12, 2023 at 1:15:40 PM UTC-5, John Larkin wrote:

The plate current would be under 1 mA when ON. I have no idea what the
grid current might be with a modest positive grid bias.

Screen grids run positive, typically at a few mA.

John, you keep saying this, but, compared to the cathode it is a negative voltage.
I\'ve looked at several schematics and the grid is negative to the cathode.
The more negative the grid goes the less current.
Where\'s the disconnect?
Thanks, Mikek

 

[John Larkin]

On Fri, 12 May 2023 11:41:52 -0700 (PDT), Lamont Cranston
<amdx62@gmail.com> wrote:

On Friday, May 12, 2023 at 1:15:40?PM UTC-5, John Larkin wrote:

The plate current would be under 1 mA when ON. I have no idea what the
grid current might be with a modest positive grid bias.

Screen grids run positive, typically at a few mA.

John, you keep saying this, but, compared to the cathode it is a negative voltage.

I propose to drive the grid positive. I know, DONT DO THAT.

>I\'ve looked at several schematics and the grid is negative to the cathode.

Lack of imagination.

The more negative the grid goes the less current.
Where\'s the disconnect?
Thanks, Mikek

I was playing with some enhancement mode PHEMTs that have an abs max
positive gate voltage of 0.7. They start to get interesting around
1.2.

 

[Lamont Cranston]

On Friday, May 12, 2023 at 2:51:36 PM UTC-5, John Larkin wrote:

On Fri, 12 May 2023 11:41:52 -0700 (PDT), Lamont Cranston
amd...@gmail.com> wrote:
On Friday, May 12, 2023 at 1:15:40?PM UTC-5, John Larkin wrote:

The plate current would be under 1 mA when ON. I have no idea what the
grid current might be with a modest positive grid bias.

Screen grids run positive, typically at a few mA.

John, you keep saying this, but, compared to the cathode it is a negative voltage.
I propose to drive the grid positive. I know, DONT DO THAT.
I\'ve looked at several schematics and the grid is negative to the cathode.
Lack of imagination.
The more negative the grid goes the less current.
Where\'s the disconnect?
Thanks, Mikek
I was playing with some enhancement mode PHEMTs that have an abs max
positive gate voltage of 0.7. They start to get interesting around
1.2.

OK John.
I suspect I\'ll be needing a low voltage power supply, for the bias.

What Voltage supply should I start building? Or make it adjustable up to ?V..

Starting through my junque, I doubt I have any 6.3V transformers anymore,
Probably just make a 6.3Vdc heater supply.
Your thoughts?
Mikek

 

[John Larkin]

On Fri, 12 May 2023 13:25:24 -0700 (PDT), Lamont Cranston
<amdx62@gmail.com> wrote:

On Friday, May 12, 2023 at 2:51:36?PM UTC-5, John Larkin wrote:
On Fri, 12 May 2023 11:41:52 -0700 (PDT), Lamont Cranston
amd...@gmail.com> wrote:
On Friday, May 12, 2023 at 1:15:40?PM UTC-5, John Larkin wrote:

The plate current would be under 1 mA when ON. I have no idea what the
grid current might be with a modest positive grid bias.

Screen grids run positive, typically at a few mA.

John, you keep saying this, but, compared to the cathode it is a negative voltage.
I propose to drive the grid positive. I know, DONT DO THAT.
I\'ve looked at several schematics and the grid is negative to the cathode.
Lack of imagination.
The more negative the grid goes the less current.
Where\'s the disconnect?
Thanks, Mikek
I was playing with some enhancement mode PHEMTs that have an abs max
positive gate voltage of 0.7. They start to get interesting around
1.2.

OK John.
I suspect I\'ll be needing a low voltage power supply, for the bias.

I have a nice little circuit in mind. I\'ll post it after Sloman shows
us his, any minute now.

What Voltage supply should I start building? Or make it adjustable up to ?V.

Starting through my junque, I doubt I have any 6.3V transformers anymore,
Probably just make a 6.3Vdc heater supply.
Your thoughts?
Mikek

You will need a filament supply. A 6-volt DC wall-wart would be good.

 

[Lamont Cranston]

On Friday, May 12, 2023 at 3:38:19 PM UTC-5, John Larkin wrote:

On Fri, 12 May 2023 13:25:24 -0700 (PDT), Lamont Cranston
amd...@gmail.com> wrote:
On Friday, May 12, 2023 at 2:51:36?PM UTC-5, John Larkin wrote:
On Fri, 12 May 2023 11:41:52 -0700 (PDT), Lamont Cranston
amd...@gmail.com> wrote:
On Friday, May 12, 2023 at 1:15:40?PM UTC-5, John Larkin wrote:

The plate current would be under 1 mA when ON. I have no idea what the
grid current might be with a modest positive grid bias.

Screen grids run positive, typically at a few mA.

John, you keep saying this, but, compared to the cathode it is a negative voltage.
I propose to drive the grid positive. I know, DONT DO THAT.
I\'ve looked at several schematics and the grid is negative to the cathode.
Lack of imagination.
The more negative the grid goes the less current.
Where\'s the disconnect?
Thanks, Mikek
I was playing with some enhancement mode PHEMTs that have an abs max
positive gate voltage of 0.7. They start to get interesting around
1.2.

OK John.
I suspect I\'ll be needing a low voltage power supply, for the bias.
I have a nice little circuit in mind. I\'ll post it after Sloman shows
us his, any minute now.

What Voltage supply should I start building? Or make it adjustable up to ?V.

Starting through my junque, I doubt I have any 6.3V transformers anymore,
Probably just make a 6.3Vdc heater supply.
Your thoughts?
Mikek
You will need a filament supply. A 6-volt DC wall-wart would be good.

Yes John, I need two low voltage supplies one for filament and the other for bias.
I\'ll be building on a metal box I hope, transformer and Tube on top, LV supplies, and timer inside.
If I don\'t have a 6.3V transformer, I plan to build a 6.3Vdc supply for the heater.
What voltage should I build the Bias supply? Or adjustable, up to what?
Thanks, Mikek

 

[Phil Hobbs]

On 2023-05-12 14:15, John Larkin wrote:

On Fri, 12 May 2023 13:33:29 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 2023-05-12 10:09, John Larkin wrote:
On Fri, 12 May 2023 11:30:39 -0000 (UTC), Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

John Larkin <jlarkin@highlandSNIPMEtechnology.com> wrote:
On Thu, 11 May 2023 18:00:42 -0700 (PDT), Lamont Cranston
amdx62@gmail.com> wrote:

On Thursday, May 11, 2023 at 7:36:56?PM UTC-5, John Larkin wrote:

Positive on the grid would help drive the plate closer to ground.

Look at the 6BK4 transfer curves. Plate current is increasing hard as
grid voltage is increasing past 0 volts. We are literally in uncharted
territory.

The curve doesn\'t show grid voltage increasing past 0 Volts.

They stopped graphing, but the slope is steep at 0 volts. It ain\'t
going to flatten out at +1.

Positive on the grid will accelerate electrons towards the plate. And
draw a little grid current.

But I can now see, if I use the 20,000 volt line,
with -12V on the grid 0 ma of currents flows.
with -10V on the grid 0.06 ma of currents flows.
with -8V on he grid 0.375 ma of currents flows.
with -5 on the grid 1.35 ma of currents flows.
with -3V on the grid 2 ma of currents flows.

What you really need is lines for +1000 and +250 on the plate, but the
people who designed this tube never expected it to be used as a
saturating switch.

It would be interesting to test it as a switch with positive grid
voltage. I guess you will!



So as the grid voltage goes less negative (positive direction) more current flows.
Thanks, Mikek
P.S. Tube, socket, 2N7000s, some 2W, 1.5M? High Voltage resistors ordered.
Resistors are for voltage divider to my used with a multi voltage experiment.


One reason for the choice of graph limits is to protect the tube. Grid
heating isn’t an issue at +1 V_g-k, but cathode damage may be.

Cheers

Phil Hobbs

There is very little to be googled about using tubes with positive
grid voltage. Most people just ignore the possibility, or say DONT DO
IT.

I did find an interesting study on the subject. It\'s from 1933 and
it\'s still paywalled after 90 years.

But I do still have the 1964 edition of the RCA Transmitting Tube
manual, nice bedtime reading. Driving big transmit jugs with positive
grid voltage is the way to get RF power. Some data sheets have curves
that don\'t show anything below zero but go to +300 on the grid. The
current enhancement, as compared to Idss, gets up into the 20:1 and
even 50:1 range.

Based on these curves, I wild-guess that my imagined circuit could
enhance a wimpy 6BK4 by something like 2:1 or maybe 5:1, which it
probably needs.


Big transmitting tubes usually have directly-heated tungsten cathodes,
which are bulletproof but have low emission at a given temperature.

Oxide cathodes are much stronger emitters, but are far more delicate.
Some are designed to run at full emission, e.g. in your 5U4 rectifier.

Most receiving tubes can be permanently damaged by pulling too much
cathode current. See e.g. Wegener, \"The Oxide-Coated Cathode\"

https://electrooptical.net/OldBooks/OxideCoatedCathodV1.djvu
https://electrooptical.net/OldBooks/OxideCoatedCathodeVol2.djvu

Cheers

Phil Hobbs

We\'d expect maybe a few mA peak cathode current, and that might be at
a 10% duty cycle, and this is a science project. It would probably be
OK.

The plate current would be under 1 mA when ON. I have no idea what the
grid current might be with a modest positive grid bias.

Screen grids run positive, typically at a few mA.

Sure, it\'ll be fine for that. I was addressing the more general
question of why you don\'t want to run too high a cathode current for a
given tube, if you\'re making 50,000 All-American Fives and don\'t want a
lot of warranty returns.

Cheers

Phil Hobbs

--
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

 

[John Larkin]

On Fri, 12 May 2023 13:43:56 -0700 (PDT), Lamont Cranston
<amdx62@gmail.com> wrote:

On Friday, May 12, 2023 at 3:38:19?PM UTC-5, John Larkin wrote:
On Fri, 12 May 2023 13:25:24 -0700 (PDT), Lamont Cranston
amd...@gmail.com> wrote:
On Friday, May 12, 2023 at 2:51:36?PM UTC-5, John Larkin wrote:
On Fri, 12 May 2023 11:41:52 -0700 (PDT), Lamont Cranston
amd...@gmail.com> wrote:
On Friday, May 12, 2023 at 1:15:40?PM UTC-5, John Larkin wrote:

The plate current would be under 1 mA when ON. I have no idea what the
grid current might be with a modest positive grid bias.

Screen grids run positive, typically at a few mA.

John, you keep saying this, but, compared to the cathode it is a negative voltage.
I propose to drive the grid positive. I know, DONT DO THAT.
I\'ve looked at several schematics and the grid is negative to the cathode.
Lack of imagination.
The more negative the grid goes the less current.
Where\'s the disconnect?
Thanks, Mikek
I was playing with some enhancement mode PHEMTs that have an abs max
positive gate voltage of 0.7. They start to get interesting around
1.2.

OK John.
I suspect I\'ll be needing a low voltage power supply, for the bias.
I have a nice little circuit in mind. I\'ll post it after Sloman shows
us his, any minute now.

What Voltage supply should I start building? Or make it adjustable up to ?V.

Starting through my junque, I doubt I have any 6.3V transformers anymore,
Probably just make a 6.3Vdc heater supply.
Your thoughts?
Mikek
You will need a filament supply. A 6-volt DC wall-wart would be good.

Yes John, I need two low voltage supplies one for filament and the other for bias.
I\'ll be building on a metal box I hope, transformer and Tube on top, LV supplies, and timer inside.
If I don\'t have a 6.3V transformer, I plan to build a 6.3Vdc supply for the heater.
What voltage should I build the Bias supply? Or adjustable, up to what?
Thanks, Mikek

Where\'s Sloman\'s design? I really wanted to see that.

Here\'s a suggestion.

https://www.dropbox.com/s/lm7aqo3e3892hhb/6BK4_Pulser_1.jpg?raw=1

It needs to be tested and maybe tweaked. I haven\'t designed with tubes
lately.