CRT vertical/horizontal amp ideas...

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

Hello Frank,

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:

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

Regards, Joerg

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

Thanks for the reply.

from

'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

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:

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

Google on HV op-amps a bit.

Good day!

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

-frank

Hello Mike,

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

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 +/-

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

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 +/-

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