The Devil in control Flying spot PMT head amp build

[Harry Dalek]

The idea here is use the Devil monitor to feed a slave oscilloscope for a Raster for a PMT flying spot camera .
I want to make it more versatile than i was originally thinking other than imaging a slide or hand drawn test card on a transparency i was thinking i may as well go the whole hog and make it a all round PMT flying spot CRT camera the scope does the scanning and the PMT head amp the pickup of the video part.
The one problem i can see the monitor is only in sync to NBTV 32 line standard or any standard it can do when its fed a video of that standard free running those oscillators are not so i have to see if i can adjust the saw tooth oscillators manually to frequency .
Reason i have not made panel controls for the devil still getting my head around these extra controls that it looks like i will need.
I think it should still work feeding the video back to the Devil from the head amp in the loop as its the same idea as Ralph Taggart's SSTV Flying sopt camera monitor idea apart from this is NBTV and hes was a transparency scanner as i recall .
viewtopic.php?f=27&t=2288&hilit=ralph

Another problem i am not sure i will use this pmt would like to i have no data for it but i do see k for cathode on the base and its not to hard to follow the connections and it will more than likely be run under 600 volts ...i will have work it out so i change this tube if need be,

[Harry Dalek]

I ended up finding more data on the EMI 9524 and its equivalents so i have used this one this time ,the PMT is wired up and the head amp is finished as well i will do some testing tomorrow and if all go's well make sure the case is light proofed and run the PMT in as i did with the PMT Nipkow camera a while back .
But see how it gos'.

[Harry Dalek]

Light proofing my case today ,had to cover 2 large holes and see what panel controls i could use also help in covering old panel control holes the trials of repurposing a case ....have a lens cap which i have taped shut as well just in case it pops off by mistake while testing the pmt .
Hooked up the pre amp but i hooked it up with dual supply wrong way around ...! the op amps heated up a touch in the few seconds i realised .with fingers crossed reversed the the supply to its correct polarity...seemed to work closed the case and tested the PMT watching the scope worked first up as i recall from results with last PMT switched it off and second test i was not seeing the static i was expecting from the first go i think the PMT is fine but the first op amp is now playing up getting gain adjustments from the second opamp and can see high voltage adjustments to the PMT are still happening viewing the scope but i can also see i have a problem ..scope result pretty meaningless as a still i would be worried if i had not seen the first go ...see if i can do better next posting .

[Harry Dalek]

Having a look after work today i opened the case and found the first preamp IC half out of its socket must of pulled it a touch to say the least when fitting the wiring in .
I know the PMT is working now as its a very dark this winter day and rain coming down i noticed moving my hand around the case i was getting a level indication on the scope i was thinking its was the top of the case i had light proofed but i found it was around the lens the lens cap i had taped on there must be a few photons making there way in as it sure shows up .
This one also seems to run at the 500 600 volt range well so far .

[Harry Dalek]

More testing today running the PMT ,i tried a higher voltage here and adjusted the preamp .
The second youtube video the little light still getting into that pmt case shows up well on the scope and shows the PMt is sure still light sensitive .
I tried an led with 100k resistor it picked that up via a voltage test but no luck on modulation test i will work on that next .

youtu.be/Ai0MjcrscY4

youtu.be/DYHfwro3ysQ

[Harry Dalek]

Re: Photomultiplier Tubes

by Klaas Robers » Wed Aug 17, 2016 7:23 pm

Harry, running an LED from an adjustable voltage is not the way to do it. Much better is an adjustable current (mA or even more uA). That is easily obtained by circuiting a resistor in series with the LED. Then a potentiometer is an adjustable resistor, so you can go into all directions. The big advantage of a resistor is too that you may use a square wave generator that gives say 5 volts and use that with the adjustable resistor (potentiometer) in series to have a fast switching LED. You can see that on the oscilloscope.

I never got around to trying this correctly Klass and its pretty important i get this right in testing for this one .
Will pretty much know the idea for this tacked on side of the project will work when i see a clean video via a led transmission to the pmt preamp out .
Am just checking do you mean Klass the the circuit on the right ?
i have a bit of time tomorrow any advice here on the best circuit here to try ,i used my circuit last time but it didn't give great results here voltage driving the led. .

[Klaas Robers]

I would prefer the circuit called "Transmitter Circuit". That one really sends a modulated CURRENT into the LED. That is what you should like.

[Harry Dalek]

I would prefer the circuit called "Transmitter Circuit". That one really sends a modulated CURRENT into the LED. That is what you should like.

Thanks Klass i ended up having to go out to night i will build that one tomorrow morning and give it a go .

[Harry Dalek]

I finished the new led light transmitter and tried it in my PMT case via another 3 colour led but only on the green Led light as thats what its going need to see the green trace of a oscilloscope .
Looking back to my past PMT test doing the same test but with a different light transmitter circuit results there were red was best and blue worst green in between .
viewtopic.php?f=20&t=2139&start=45

With tweaking every thing i could think of looking at todays test the top trace is the NBTV reversing wav video file input of circuit bottom trace the ouput of the preamp best i could sort of get it this time ,its waveform is still distorted but i think better than the last PMT go .
I had the led in the case cabled out to power to the light transmitter circuit but i did have the second led on the board still viewable so in parallel really with the one in the PMT case ....this could be a factor i can switch it off on the board .

Any suggestions welcome on improving this i think as last time Klass mentioned its more the way i am driving the led ... If i have to rebuild the transmitter so be it .

[Klaas Robers]

I think the PMT is saturated, far too much light. make the 100 ohm resistor in the emitter lead much higher, 1k or 10k. Then you get (much) less light out of the LED. PMTs have to work in the shade, or even better in the dark.

[Harry Dalek]

I think the PMT is saturated, far too much light. make the 100 ohm resistor in the emitter lead much higher, 1k or 10k. Then you get (much) less light out of the LED. PMTs have to work in the shade, or even better in the dark.

Could very well be the case Klass i think also theres a light little problem .....as it is making its way also from around the lens area i have covered ,i will work on this as well i recall how little was needed on the Nipkow pmt camera to cause noise staticy picture it was always the case there was a tiny scratch on the case paint letting some light in .
Pretty much Led running for the pmt its not viewable to my eyes
I will adjust the circuit tomorrow and more light proofing and retest .Thanks for the advice Klass

[Harry Dalek]

The video i am now getting is much sharper but closest i can get it to look like the input waveform today.
The adjustment to the circuit with increased resistance at the emitter of the BC548 does help ...i found i had to set the 10k to 0 ohm other wise i didn't get viewable waveform different still a touch as it is to the input waveform ....the 1k connected to the positive and 10k trimmer is showing 550ohm in circuit the 22k i added to the 100ohm at the emitter is adjusted to 11.40k...varying the PMT voltage about 700 volts is about right and seems to work down to 300 .
I think the video is being inverted i am using CA3140s instead of TL071...i found last time the preamp worked with a range of opamps but teh CA3140 did invert the signal...I will keep working on it .

[Harry Dalek]

I changed the opamps in the preamp for Ne5534 pretty much what i have used in the PMT NBTV camera.
I looked at again at the preamp and feeding the reversing wav direct to the preamp and see what comes out ,wasn't perfect but better than before .
The PMT test Led green light test after the waveform is a bit rounded least its starting to look like what going in .

[Klaas Robers]

This looks already much better, however I see some lag, something that looks like afterglow of a phosfor. But there is no phosfor, so, what can it be? Is this with the PMT on 300 volt? May be that is the problem? Are PMTs getting much slower if they are on a lower voltage?

I would first look with the oscilloscope on the base of the transistor and on the emitter of the transistor. There should be wave forms comparable, if not identical to the input wave form. If that is the case, the LED output will be Ok.

[Harry Dalek]

This looks already much better, however I see some lag, something that looks like afterglow of a phosfor. But there is no phosfor, so, what can it be? Is this with the PMT on 300 volt? May be that is the problem? Are PMTs getting much slower if they are on a lower voltage?

I am running the PMT in the 500 to 700 volt range i have tried higher and lower voltages around that range it seems correct ...i can show you what happens with a range voltage change i have it in about 2 hundred volt jump from memory low setting 300 400 volts highest i can go is about 1600 volts ,never had to use the higher range apart from running the tube in at 1000 volts .
The lag i am not sure about may be its just the dual trace difference and the camera factor .

I would first look with the oscilloscope on the base of the transistor and on the emitter of the transistor. There should be wave forms comparable, if not identical to the input wave form. If that is the case, the LED output will be Ok.

[/quote]

Yes have to track down where the problem is there are a few factors i can see The PMT circuit but this seems to be working .the circuit i am using below ..one thing i have 980k on the anode to ground as i recall same circuit for the PMT camera ..not on this the preamp connected to this circuit as shown ...perhaps a gain control pot about 1meg around here might drop the level to the preamp touch let the waveform keep its shape than over loading the first preamp ic but it does had diodes as a limiter thats why i never bothered /
Yes also i will look into the light transmitter and take those scope readings see if thats the problem..has to be that or the preamp..post up results tomorrow .