Photomultiplier Tubes camera build

[Steve Anderson]

If Fig.7 applies to the 6199 and it's the type you're using you may as well use their suggested circuit. The gain varies with the supply voltage greatly. A change from 900 to 1000V can easily double the gain - it does vary on the type of tube and each example too.

The way you've wired the tube base is fine, it's the way most do it.

'Reasonably close' for the pre-amp is how I'd put it, don't fret over a few inches, but remember this is a high impedance arrangement so you need to be careful with hum and interference pick-up.

Steve A.

[Harry Dalek]

If Fig.7 applies to the 6199 and it's the type you're using you may as well use their suggested circuit. The gain varies with the supply voltage greatly. A change from 900 to 1000V can easily double the gain - it does vary on the type of tube and each example too.

The way you've wired the tube base is fine, it's the way most do it.

'Reasonably close' for the pre-amp is how I'd put it, don't fret over a few inches, but remember this is a high impedance arrangement so you need to be careful with hum and interference pick-up.

Steve A.

Yes Fig 7 is the RCA So a variable supply here could be of use to match it to the tube they seem temperamental.... for what ever i know the PMT might be a dud but i will get some learning out of it finding out either way .
I think it said in the data 500 volts was the lowest of the voltage range for it to work i will double check that .

OH That PMT base photo is an example i am not that far yet ,i noticed others were wiring theres up like this my plan was to do the same if it was correct or mattered..

I noticed you had your tube was wrapped in foil to light proof it your light sensitive area was on the side of the pmt so you must of left a slot for testing ,mines more like a image tube at the top but i was wondering light could come from the back side of the tube so should be wrapped to light proof it ? i would put it in a case for that reason but every thing helps ...also these are cold cathode tubes but do they get warm ?

[Klaas Robers]

Harry, be careful that you NEVER operate the tube in normal room lighting. You can place the tube in a closed shoebox, but then you should be sure to remove the high voltage before you open the box. If you forget that once, the tube is ruined. And yes, light can also reach the target (cathode) from the sides.

In practical situations the set-up is such, that when you open the box that the votage is switched off by a contact and the resistor divider is shorted by the same contact, well preferably by a different contact. I missed this very much in my SSTV Handbook written by Ralph Taggart. This is too in cabinets of large tube transmitters, where there is some kV needed inside the cabinet.

Safety first.

[Steve Anderson]

Without reviewing my notes for the PMT thread I can't recall what function the foil wrapped around the tube was for. I do remember that it was connected to the cathode, so it's at -1000V - great care is needed. I'll have to do some digging. It probably is mentioned in the manuals I recently uploaded.

Stray light could enter from other directions other than that intended, but that wasn't the prime purpose of the foil, it did serve that secondary function though.

The tubes run cold - or very nearly so. The maximum rated current is usually around 1mA, so at 1000V that's 1W. Most of the time it will/should be under 100uA, 100mW, you can forget about heat in practice.

Klaas's advice on fitting an interlock to cut the power to the tube should the lid/door on the device be open while power is on is sound. The switch needs to be in the -ve DC supply just before the tube socket not in the AC 220V feed as the capacitors in the power supply take time to discharge. I'm not sure how quickly these devices get destroyed, probably fairly quickly. The problem is the switch/microswitch needs to be rated for these voltages - not many of those around.

Steve A.

[Harry Dalek]

Thanks Steve Klass for the advice some things on the PMT that i was not sure about .
I have not really started on any thing with them yet as i have been gathering information and past projects on this forum here are good seeing what was tried .
I had noticed Peter Yanczer had an auto cut off Klass but your idea is alot easier....its funny as i have been thinking about this all day perhaps your cut off circuit Peters would both be a good idea for a camera try at that stage .
All much of muchness doing the same but no voltage to me sounds safe yes Steve i will .

Steve i noticed you had your tube and circuit in a tin with a blue led lid shut modulating the led this is how i think you were testing the PMT ...the foil i will have another review .

I might use the same idea but with a UV led .
I think i might find a tube or wrap it to in something to light proof the tube so no light effects it from the back ,i will have a think to about that i know it needs to be in a light proof case of some sort.

Well have to start some where
I have also been thinking of the power supply for the PMT and have read the advice given to the few that have also asked about this on the forum, i can make either a 50hz inverter mains or battery power supply powered or pinch an old broken lap tops fluro display inverter they are all around 1000v .
Thinking about trying the same spare 2nd HV module i am trying on the SSTV project for this just run it at a lower voltage to get no 1000v with a fixed resistor LM317 regulator feeding it to keep it safe ...its well regulated small and something i don't have to do all depends on how low a voltage range it operates at .....Testing it will see either way ! any case a few options to try .

[Harry Dalek]

Having a think about the PMT tube testing ,i am sort of more worried about braking it than any thing so looking for something to enclose it in for light tests i think i will try the tube idea and thanks to an empty clive of india authentic curry powder container this might do the trick ...the red lid is not light proof yet but i will work on that perhaps a layer of foil .
The tube is longer than the PMT so i could fit an led to modulate in the front in side the tube so as with Steve A tests in he's tin this should also be similar.
Thinking still about wiring the power supply resistors caps for the dynodes will be on the tubes connections then i just really have 4 wires out ground ,high voltage negative and anode out and what ever to modulate the uv Led .
Reading the below site on he's first experiments on PMT starting on a low voltage and working up ..not great light proofing but must effect results .
Labguy's world http://www.labguysworld.com/PhotomultiplierTubes.htm

[Klaas Robers]

Harry, no need for a UV LED. The PMT is also sensitive to green light and even to red light, it is only LESS sensitive. And as there is no problem at all with the sensitivity of PMTs, you can use any colour. You have to squeeze the current any way to very low values.

[Harry Dalek]

Harry, no need for a UV LED. The PMT is also sensitive to green light and even to red light, it is only LESS sensitive. And as there is no problem at all with the sensitivity of PMTs, you can use any colour. You have to squeeze the current any way to very low values.

Oh ok Klass thats interesting so they do have a bit of a range i didn't know that i was thinking uv or down to blue was it but i do have many UV leds for when i was experimenting with glow paint but i will try other colour leds ,my main interest is seeing if the PMT is working more than its colour range .

Just getting every thing together to like a jigsaw puzzle so i can start on it this week.

[Harry Dalek]

Worked on the PMT light proofing some more ,found a spice lid that fits like a lens cap so that came in handy and cut a thin card board roll and wrapped that around the tube to light proof that part was going to just use the foil but with this it slides on and off if needed .
Could just about test as but to make sure i will use the other as a test chamber with an led fitted.

Reading the data again it does point out the tube can be effected by light even with no voltage to the tube ...these things are fussy

Are filters a good idea to drop light levels to the light sensitive area ? might be of use in the future if used in higher light levels just wondering if any ones tried it .

I didn't have a socket for this tube so wrapped copper wire around the connections and can now solder the 470k resistors to those still have to locate the caps needed.

Still looking at power supply options ,this tiny printer scanner inverter used for the scanning light last time i tested it it was around the right voltage range ,my modules run a bit to high for this tube after testing them would have to use a string of high meg resistors to drop so i will do some more testing tomorrow ..on the inverter.

I was reading also on this tube they are very much like LNBS cool them down and you lower the noise level PMTs must all be similar like this .

[Steve Anderson]

Imagine sitting a totally darkened room for an hour, and I mean totally darkened. You see the slightest glimmer of light - just. That's far too much for a PMT. I couldn't see the blue light the 931As were responding to, even after my eyes were dark-adapted.

If you have a lot of light (as far as a PMT is concerned) keep the volts at the very low end. Don't exceed the maximum tube current - it's so easy to do!

Steve A.

[Harry Dalek]

Imagine sitting a totally darkened room for an hour, and I mean totally darkened. You see the slightest glimmer of light - just. That's far too much for a PMT. I couldn't see the blue light the 931As were responding to, even after my eyes were dark-adapted.

If you have a lot of light (as far as a PMT is concerned) keep the volts at the very low end. Don't exceed the maximum tube current - it's so easy to do!

Steve A.

Wow no wonder they are also used detecting particles from outer space.
After reading lab guy's experiments he started off the tubes on low voltage 300 or so and worked up my data say's 500 volts is the minimum for this one ,seeing he also did a a quick and dirty flying spot scanner the voltage to the PMT must be very critical or light from the little monitor he was pointing the pmt at would other wise over load it or damage it at full 1000 volts .
So yes Steve i will start off so my power supply can adjust the voltage to the PMT.
Still a little work to go before i test it but getting there .

[Harry Dalek]

Reading advice posted here and what i have read else where the power supply for the PMT had me thinking it would be wise to make it adjustable at least and i can run it up from a safe level and have some thing i can use on the other PMT's for testing later .

So having got a spare case the other day from a reuse shop used for a computer tape drive ,i plan to work on this for the PMT supply ...it has a working switch mode working power supply positive 12 volts 5 volts no negative supply in this .

I know it's easy to do a back to back 240 transformers what ever 12 volt to 12 volt AC to 240 or there abouts to start off with but i want variable ,Using the circuit below with junk box parts i have some 4047 ic's handy used one of those and 2 Power MOSFET IRFP250 swapping those for the irfz44 .

I have variable lm317 feeding the transformers center tap getting 30 volts to 274 volts ac out with that used ,need to multiply the AC now for the high voltage negative .

Thats the next step .

I looked into using laptop lcd fluro display inverter and the scanner fluro inverter both work but i had trouble getting a AC reading with my HV probe and multimeter may be its the frequency they work at ,i couldn't get a meter reading unless it was sparking or i think under load .... i broke the fluro so couldn't double check this .

[Harry Dalek]

Well the power supply has put me a step back its to noisy looking at it on a scope , i am picking it up even no where near connecting it to the inverter ,i checked with my other inverters module's and same problem ,I think it would be wise to start again on something cleaner till i know it works then try an inverter and see.... others have used them so they must be alright want to to make sure this is not a problem from the start....

I want some thing clean so will have to go with either my 3bp1 valve radio transformer AC supply and a multiplier or build back to back isolating transformer idea ,had a look at this today getting around 400 volts ac with this method and with the size of the transformers looking a touch safer to go with this i am thinking .

Its a touch still to small for Steve A voltage doubler looking more at what i was using on the inverter as in Klaas reworked Peter Yanczer design also noticed this other version the caps in brackets voltage ratings are a bit of a problem on this one .

I only have 10 uf 450 volts caps but seemed to work on the inverter .

[Steve Anderson]

Harry, inverters simply by the way they work are generally noisy. I wouldn't even consider one for a PMT supply. There are probably exceptions but they're unlikely to be found in any domestic or office piece of gear.

Do it yourself, where you have control and if it isn't still good enough consider and examine why. When it's designed in some far-off land to be the cheapest possible - what can you expect? The only criteria in the far-east is it must be cheaper. Bugger quality, performance or reliability. It works in the shop, it doesn't when you get it home. Been there many a time.

If it says, "Made in China" as a finished product, I don't buy it and place it back on the shelf. Something like semiconductors supervised by Philips, Motorola, Microchip, etc, that's OK. You're fairly sure that the product meets the required standards. But something made by the, "Golden Dragon Electronics Corp.", think again.

If there is such a company (most likely) I apologise in advance. I have never bought one of your products for the reasons above. Now you know why.

Psst..they can do it, they just don't want to - it's a mindset.

Steve A.

[Harry Dalek]

Harry, inverters simply by the way they work are generally noisy. I wouldn't even consider one for a PMT supply. There are probably exceptions but they're unlikely to be found in any domestic or office piece of gear.

Hi Steve
I really didn't expect what i got ,reading past posts that Steve O 3 colour camera used one and late great Peter Y had a 555 timer version for he's didn't really see this mentioned as a problem but i sure saw it , checking with my scope to the point of a RF scope reading now thats a problem indeed!

Do it yourself, where you have control and if it isn't still good enough consider and examine why. When it's designed in some far-off land to be the cheapest possible - what can you expect? The only criteria in the far-east is it must be cheaper. Bugger quality, performance or reliability. It works in the shop, it doesn't when you get it home. Been there many a time.

Well as far as design if you mean the original inverter i checked it against other inverters i have and as you say they are all noisy i don't now understand how it could be used with a PMT as in all inverters ,thats why i knew i need some thing basic and clean for something like these tubes .
Some times Steve it does not work at all ! only happened to me one time off ebay with a USB stick when they were new thing and this one from China a few years ago i did end up buying one and it was a dud made never to work but they must of spent more the the packaging to make it look real ...

If it says, "Made in China" as a finished product, I don't buy it and place it back on the shelf. Something like semiconductors supervised by Philips, Motorola, Microchip, etc, that's OK. You're fairly sure that the product meets the required standards. But something made by the, "Golden Dragon Electronics Corp.", think again.

If there is such a company (most likely) I apologise in advance. I have never bought one of your products for the reasons above.

Steve A.

[/quote]

Well thats something to keep on mind thats a hard one as they are slowly but surely making every thing ,i suppose your saying whats on the thing sold unless they fake a product name ~!