CRT vertical/horizontal amp ideas...

[Mike Deblis]

Hi,

I'm looking for pointers to fairly low bandwidth H/V amps (and blanking
circuitry) for small electrostatic CRTs. I've found a couple of simple
designs (e.g. http://timefracture.org/clockdocs/VECTCLK_SCH.pdf), but was
wondering if anyone had any favourite references. Frequency response of
around 500kHz - 1MHz should be fine.

The CRTs I'm looking at (small Russian ones like the 3LOi) have a peak HT of
about 500V and a cut-off of about -90V.


Thanks

Mike

 

[Frank Miles]

In article <dco1vh$j69$1@inews.gazeta.pl>,
Mike Deblis <mdeblis@hotmail.com> wrote:

Hi,

I'm looking for pointers to fairly low bandwidth H/V amps (and blanking
circuitry) for small electrostatic CRTs. I've found a couple of simple
designs (e.g. http://timefracture.org/clockdocs/VECTCLK_SCH.pdf), but was
wondering if anyone had any favourite references. Frequency response of
around 500kHz - 1MHz should be fine.

The CRTs I'm looking at (small Russian ones like the 3LOi) have a peak HT of
about 500V and a cut-off of about -90V.


Thanks

Mike

Is this frequency response only in the vertical? It may be much easier
if the horizontal frequency response need not be so high.

Anyway... the standard response would be to look up the Tektronix series
of books, published decades ago, but still pertinent. The key is
the output devices, which must have low capacitance, high voltage capabilities,
and reasonable power and bandwidth (cascoding can be very helpful here).

The schematics at that web site aren't too horrible on first glance, though
you may be able to save power if the horizontal isn't run so fast (typically
the horizontal deflection factor is worse than the vertical) by using
a push-pull transistor configuration -- take a look at the horizontal
DA in the service manual for many old slower Tek analog 'scopes. Of course,
you may have trouble finding suitable devices at the required ratings
so it may be necessary to stick with the passive pullups. Non-inductive
wirewounds can be helpful here. Feedback amps were often used in the
horizontal, occasionally in the vertical for DAs in this range.

Out of curiousity, why this CRT, especially if it is "small"? Judging from
the stiff deflection factor, it has no PDA. If the screen size is small,
you're really working awfully hard to push the beam around. Maybe it's
cheap, but I doubt it will have great resolution, and we already know it
won't be fast. In short -- what's the attraction here? Why do it?
Why not LCD/digital? [I am ignorant of the particular Russian CRT]. There
may be a good answer, even if it applies only to some niche...

Hope this helps!

-frank
--

 

[Joerg]

Hello Frank,

Anyway... the standard response would be to look up the Tektronix series
of books, published decades ago, but still pertinent. ...

Or look at a schematic of a typical scope. I believe Hameg has the
manuals available for download. It's in German but once at the schematic
level that shouldn't really matter:
http://www.hameg.com/1.entry.0.html

... In short -- what's the attraction here? Why do it?
Why not LCD/digital? [I am ignorant of the particular Russian CRT]. There
may be a good answer, even if it applies only to some niche...

Ain't nothing like that nice green glow of a CRT.

Regards, Joerg

http://www.analogconsultants.com

 

[Mike Deblis]

"Frank Miles" <fpm@u.washington.edu> wrote in message
news:dco8iv$dpi$1@gnus01.u.washington.edu...


Thanks for the reply.

Out of curiousity, why this CRT, especially if it is "small"? Judging
from
the stiff deflection factor, it has no PDA. If the screen size is small,
you're really working awfully hard to push the beam around. Maybe it's
cheap, but I doubt it will have great resolution, and we already know it
won't be fast. In short -- what's the attraction here? Why do it?
Why not LCD/digital? [I am ignorant of the particular Russian CRT]. There
may be a good answer, even if it applies only to some niche...

'cos I like retro displays (nixies etc.). I want to make a clock using one
of these tubes. I realise they are stiff, but I have some! 150V is a bit
much, but eminently possible. I am very happy with PICs/AVRs etc. and
digital logic, but the sort of HV you get with with CRTs etc. is not my
forte, hence the questions.

I have a Tek 2430A sitting here, and noted from its service manual that the
X & Y deflection amps are just TL074s running off +/- 15V, so the tube is 10
times more sensitive. However, the RUski tubes are really simple to drive,
and for my application, perfectly adaquate.

I also have a 2465A (my favourite 'scope), but of course it has the magic
U800 hybrid Y amp which is its primary failure mode, so no help from that.

Also, there are amber & blue CRTs which look really very cool. A 1" diameter
tubs fits in a small enclosure with all its gubbins, and is defintely very
retro when used with an analogue clock face. You have to make the clock face
"wander" ever so slightly round the screen so that you don;t get too much
burn, but apart from that it should work pretty well...

Mike

 

[tekamn]

Hi Mike,

sorry to correct you: The X & Y deflection amps are typically NOT just
TL074s running off +/- 15V.

These are the preamp/DC-correction amps only. The real amplifier is a
sophisticated hybrid for Y like in the 2465A or the U800 IC for X.

I am not in detail familiar with your particular russian tube. IAFAIR
from my expereminet a couple of years ago, the sensivity is appr. 8V/cm
(20V/inch). So this might be the ballpark figure to design with in your
case. A low BW Tektronix cirsuit can be taken from a 422 or 453 (latter
is gross overkill in BW for your application, but may be helpful).

Go for bama.sbc.edu, follow the instructions for free download of 422
or 453. The design is fully discrete components, so you will be easy
done with the cirsuit (a well stacked junkbox at heand, so all parts
are handy).

For your clock project: Google a little bit, there are a few designs
with nixie clock and even o'scope clock around -- just as a starter
point.

hth,
Andreas

 

[Frank Miles]

In article <dcpgff$a69$1@nwrdmz02.dmz.ncs.ea.ibs-infra.bt.com>,
Mike Deblis <mdeblis@hotmail.com> wrote:

"Frank Miles" <fpm@u.washington.edu> wrote in message
news:dco8iv$dpi$1@gnus01.u.washington.edu...


Thanks for the reply.

Out of curiousity, why this CRT, especially if it is "small"? Judging
from
the stiff deflection factor, it has no PDA. If the screen size is small,
you're really working awfully hard to push the beam around. Maybe it's
cheap, but I doubt it will have great resolution, and we already know it
won't be fast. In short -- what's the attraction here? Why do it?
Why not LCD/digital? [I am ignorant of the particular Russian CRT]. There
may be a good answer, even if it applies only to some niche...

'cos I like retro displays (nixies etc.). I want to make a clock using one
of these tubes. I realise they are stiff, but I have some! 150V is a bit
much, but eminently possible. I am very happy with PICs/AVRs etc. and
digital logic, but the sort of HV you get with with CRTs etc. is not my
forte, hence the questions.

I have a Tek 2430A sitting here, and noted from its service manual that the
X & Y deflection amps are just TL074s running off +/- 15V, so the tube is 10
times more sensitive. However, the RUski tubes are really simple to drive,
and for my application, perfectly adaquate.

I also have a 2465A (my favourite 'scope), but of course it has the magic
U800 hybrid Y amp which is its primary failure mode, so no help from that.

Also, there are amber & blue CRTs which look really very cool. A 1" diameter
tubs fits in a small enclosure with all its gubbins, and is defintely very
retro when used with an analogue clock face. You have to make the clock face
"wander" ever so slightly round the screen so that you don;t get too much
burn, but apart from that it should work pretty well...

Mike

Ok. Slow it down -- you will save big time on reducing power consumption,
and make device selection much easier. Reliability will increase.

-frank
--

 

[Chris Carlen]

Mike Deblis wrote:

"Frank Miles" <fpm@u.washington.edu> wrote in message
news:dco8iv$dpi$1@gnus01.u.washington.edu...


Thanks for the reply.

Out of curiousity, why this CRT, especially if it is "small"? Judging
from
the stiff deflection factor, it has no PDA. If the screen size is small,
you're really working awfully hard to push the beam around. Maybe it's
cheap, but I doubt it will have great resolution, and we already know it
won't be fast. In short -- what's the attraction here? Why do it?
Why not LCD/digital? [I am ignorant of the particular Russian CRT]. There
may be a good answer, even if it applies only to some niche...

'cos I like retro displays (nixies etc.). I want to make a clock using one
of these tubes.

Me too. I have been planning to build a nice generic XY display from an
old 3" CRT to use as a monitor for a laser graphics projector when I
don't want to bother turning on the laser and putting wear on the galvos.

When I was in high-school I built one of Heathkit's O-scope kits. The
deflection amps did at least 150V, and were not terribly complex. I
even understood them about 75% at the time. I would try to get the
schematics for some old Heathkit scopes. Might be a little simpler than
a Tek, but who knows.

Also, Apex Microtechnology:

http://eportal.apexmicrotech.com/mainsite/index.asp

probably has something suitable, but you won't want to pay their prices.

Google on HV op-amps a bit.



Good day!



--
_______________________________________________________________________
Christopher R. Carlen
Principal Laser/Optical Technologist
Sandia National Laboratories CA USA
crcarleRemoveThis@BOGUSsandia.gov
NOTE, delete texts: "RemoveThis" and "BOGUS" from email address to reply.

 

[Joerg]

Hello Mike,

I have a Tek 2430A sitting here, and noted from its service manual that the
X & Y deflection amps are just TL074s running off +/- 15V, ...

Check the schematics. That is very unlikely.

You can make a HV amp around an opamp. Go to page 256 bottom left of
"Art of Electronics" to see how that's done. Basically four more
transistors and some passive parts.

I believe there was also something about HV amps in a National app note
but I don't recall which on it was.

Regards, Joerg

http://www.analogconsultants.com

 

[Mike Deblis]

"tekamn" <and7@bigfoot.com> wrote in message
news:1123053806.805372.174300@g44g2000cwa.googlegroups.com...

Hi Mike,

sorry to correct you: The X & Y deflection amps are typically NOT just
TL074s running off +/- 15V.

I couldn't find any hybrid amps like the ones in the 2465. The 2430A is a
digital scope, so I expect the scan rates are far slower, thus no need for
hybrid one-offs.

Looking at the service manual, "Display output", schematic 18, U460B/C a 1/2
of a TL074 is directly connected to the Y plates, and U392C/D (also 1/2 a
TL074) is directly coupled to the X plates. The TL074s are driven off +/-
15V with no DC offset, thus the total swing on the plates is +15 -> -15,
and -15 to +15 or thereabouts.

I also checked the "Theory of Operation" section on "Horizontal and Vertical
Output Amplifiers", page 3-73 in my manual, where it explicitely says that
the U392 C/D drives the X plates, and likewise for U460B/C for the Y plates.

Mike

 

[Mike Deblis]

"tekamn" <and7@bigfoot.com> wrote in message
news:1123053806.805372.174300@g44g2000cwa.googlegroups.com...

Hi Mike,

sorry to correct you: The X & Y deflection amps are typically NOT just
TL074s running off +/- 15V.

These are the preamp/DC-correction amps only. The real amplifier is a
sophisticated hybrid for Y like in the 2465A or the U800 IC for X.

I couldn't find any hybrid amps like the ones in the 2465. The 2430A is a
digital scope, so I expect the scan rates are far slower, thus no need for
hybrid one-offs.

Looking at the service manual, "Display output", schematic 18, U460B/C a 1/2
of a TL074 is directly connected to the Y plates, and U392C/D (also 1/2 a
TL074) is directly coupled to the X plates. The TL074s are driven off +/-
15V with no DC offset, thus the swing on each plate is +15 -> -15 or
thereabouts.

I also checked the "Theory of Operation" section on "Horizontal and Vertical
Output Amplifiers", page 3-73 in my manual, where it explicitly says that
the U392 C/D drives the X plates, and likewise for U460B/C for the Y plates.

Mike