Photomultiplier Tubes camera build

[Harry Dalek]

Reboot on the power supply works had 2 identical transformers with two 9 Volt AC outputs per transformer so ended up connecting them as 18 volt back to back ,this gave 200 volts then multiplying this with Klass reworked multiplier getting over 1000 volts no RF this time

i have to remove the last unfinished stages as this board had more stages at one time for another project ,its pretty much same as the Klass version 6 caps 6 diodes .

[Steve Anderson]

My wife, and indeed all of her family, although of Thai birth and nationality, they have a majority Chinese blood-line. They are quite ashamed at the quality of products coming out of their heritage homeland. With something like clothing you can see while at the market if it's any good or not. With anything you plug-in - it may work at the shop, until you get it home. Try taking it back two hours later - don't bother.

If it's made in China it's likely to be crap. Period.

A couple of days ago I bought some clutch & brake fluid for our old car, it said, "Made in the UK", I was proud and full of confidence. I didn't realise that we still made anything in the UK. The '140' sticker is the price in Thai Baht, about GBP 2.50. It works fine, but I wonder why the brake reservior needs topping up so soon after a brake-pad replacement. Cheap Chinese copy brake-pads?

Steve A.

[Harry Dalek]

My wife, and indeed all of her family, although of Thai birth and nationality, they have a majority Chinese blood-line. They are quite ashamed at the quality of products coming out of their heritage homeland. With something like clothing you can see while at the market if it's any good or not. With anything you plug-in - it may work at the shop, until you get it home. Try taking it back two hours later - don't bother.

If it's made in China it's likely to be crap. Period.

A couple of days ago I bought some clutch & brake fluid for our old car, it said, "Made in the UK", I was proud and full of confidence. I didn't realise that we still made anything in the UK. The '140' sticker is the price in Thai Baht, about GBP 2.50. It works fine, but I wonder why the brake reservior needs topping up so soon after a brake-pad replacement. Cheap Chinese copy brake-pads?

Steve A.

First up hope Hong Kong was ok weather looked nasty on the news tonight /
I think we are all stuffed then as they make every thing we need ! If they want to make something they sure can copy but as you say the wanting to make it cheap as is the only problem ....as i mentioned some time back on ics i had i have no idea if whats in them is up to standard ,i think i will check out where they come from ....from now on .
We sort of had the same problem in that fluid with car being fixed 2300 bucks later on the clutch and gear box they forget to fill the little container up with it 3 days later i am again loosing my clutch pull over and find it empty ! had some in my ute so i was very lucky and not happy Yes but not much made out side Asia these days .....perhaps a good thing on what is made any where else it will have to be good if it wants to last .

On to the PMT power supply now i have a fixed voltage on the multiplier i will check the lower stages of the power supply as i don't want to fire up the pmt right away on 1000 volts ...The data does say only the maximum working voltage 2250 and lowest is 500 volts,would rather this be a variable voltage power supply ,i am not sure if later a gain control would have the same effect ...but i can take voltages off the lower multiplier stages and adjust with a resistor i suppose,
OH well don't even know if the tube is good or not yet but getting closer now to testing and finding out .

[Harry Dalek]

Pretty much finished the power supply now every thing tests fine .
I put in a dual 12 volt low voltage one as well for a preamplifier i will be using , i will be trying Steve's tested circuit...need it for the op amps.
So thats my next Step is build that preamplifier /

[Harry Dalek]

I found by accident one of my multiplier in4007 1000v diodes must of been a dud or heading that way ,after replacing it i was getting better results from the multiplier.
I ended up making this into a Photomultiplier bench top power supply as i wanted from the start and after trying a few ideas have made it a little more versatile with a wide range of negative high voltages to select ,using a switch for the back to back transformers to select either 9 to 9 volts or 18 to 18 volts ac i have 2 ranges of voltages out of the different stages of the multiplier .
On 9 volts i get .......
negative 298 550 640 730 886 .
On the 18 volts i get 570 857 1138 1420 1650 .
Not being a regulated supply the last 2 numbers in the readings there is a amount of swing with the mains voltage,not sure how fussy these tubes are to a few volts swing here and there .
I also have a regulated dual 12 volts supply for the preamplifier..........which now is the next step
Any one else thinking about this you have to have a different mind set when working with High voltages if your scared of it make it that thought will keep to alive if your not scared don't because you will get at least a shock or worse ...

[Klaas Robers]

Harry, in principle there should be no difference in the output voltages between connecting the 9V to the 9V and connecting the 18V to the 18 V. The differences between the two output voltages can only be the difference in internal resistances and other losses of the two transformers.
What you could do is to connect the 18V of the second transformer to the 9V of the first transformer. Then you may expect output voltages about half the value of 18 - 18.

Do you have a bleeder resistor at the output? That is advisable, because in this situation, once powered up, the high voltage will remain at the output for a quite long time. The bleeder resistor will discharge the charged capacitors in say half a minute and then the output is safe. In operation, the photomultiplier has the chain of resistors that may function as a bleeder, but now you have a separate power supply you should protect yourself from unwanted high voltages shock.

[Harry Dalek]

Harry, in principle there should be no difference in the output voltages between connecting the 9V to the 9V and connecting the 18V to the 18 V. The differences between the two output voltages can only be the difference in internal resistances and other losses of the two transformers.
What you could do is to connect the 18V of the second transformer to the 9V of the first transformer. Then you may expect output voltages about half the value of 18 - 18.

Do you have a bleeder resistor at the output? That is advisable, because in this situation, once powered up, the high voltage will remain at the output for a quite long time. The bleeder resistor will discharge the charged capacitors in say half a minute and then the output is safe. In operation, the photomultiplier has the chain of resistors that may function as a bleeder, but now you have a separate power supply you should protect yourself from unwanted high voltages shock.

You are dead Right Klaas my mistake yes its 9 volt to 18 and 18 to 18 ,it woks fine which is important.
Yes these voltages are dangerous and i always keep my volt meter on it when using it ,i do have an indication light and fan which help knowing its on but i rather have the meter onit as you are saying when off its takes a while for the voltage to bleed away .

So yes i do have a load bleed resistor on the out put but as i said even so i like to watch it bleed away on the meter before touching it .

I have started on Steve's preamp its known to work circuit so will use that /.i have started on it tonight so one ic is on that little board i ended up reversing the matrix board and soldering surface mount the parts just easier in some ways .,,,mounting it behind the curry tube ...the tube is lined with foil so might be good for shielding as well .

[Harry Dalek]

Pushing my eye sight a touch and trying surface mount as something different for me ,i finished the preamp apart from adding the power and input output wiring ,checking with a conductivity test what wire go's where all looks ok no shorts so looks good on this front .
The reason i have made the circuit small perhaps wishful thinking if i have success with the tube in the testing stage i can go one to something more interesting .

[Harry Dalek]

Bit more progress today mounted the preamp worked out the UV led for the light chamber,not much more to do apart from connect the PMT and test .

[Harry Dalek]

After finding i had made mistakes on the resistor dynodes ,i redid this on a little board and thats placed beside the PMT in the light proof chamber tube....Speaking to Steve about the LED i will replace the uv one with a Blue .
Since the tube is safe in its chamber wrapped around in cardboard tube foil and tape it would have to be a lucky photon to make its way into this thing as to other particles ?.
I finished the wiring and fired it up from low voltage to a touch over a thousand volts looked at the results on the scope ,it was mentioned these things are noisy and thats what i was looking at increased noise with a voltage increase .
To really know it can detect photons i need to do a very low level led test at low voltage and bring the tube voltage up till it hopefully works ...
Below the voltage tests
scope set at 1 volt per div first 2 then at over 1000 volts negative i had to drop the scope down to 5 volts per div i have the preamp trimmer still of full bit of over loading happening i think as well .
Theres a nice small program here showing the amplifying of a PMT with an increase in voltage a good time to place it with this post .

[Klaas Robers]

Harry, if you read back Steve's PMT experiments then you first should keep the LED off. Then you are looking at the "dark current". This is rather high in the beginning and decreasing in the first 100 hours that you have the PMT running in the dark. It is as if you are looking at the remains of all the light that the PMT has seen while it was not used.

Then, when the dark current has gone down, power the LED up. That is to say, start with a 100k resistor in series and a voltage of just a few volts and slowly increasing. You will see the line on your oscilloscope going up. That is the proof that the PMT works and is photo sensitive.

If the line is too noisy for you, place a small capacitor to ground at the input of your preamplifier. Value? ...... 100 pF ? If the noise is still too large for you, make it larger, 470 pF or 1 nF.

[Harry Dalek]

Harry, if you read back Steve's PMT experiments then you first should keep the LED off. Then you are looking at the "dark current". This is rather high in the beginning and decreasing in the first 100 hours that you have the PMT running in the dark. It is as if you are looking at the remains of all the light that the PMT has seen while it was not used.

Then, when the dark current has gone down, power the LED up. That is to say, start with a 100k resistor in series and a voltage of just a few volts and slowly increasing. You will see the line on your oscilloscope going up. That is the proof that the PMT works and is photo sensitive.

If the line is too noisy for you, place a small capacitor to ground at the input of your preamplifier. Value? ...... 100 pF ? If the noise is still too large for you, make it larger, 470 pF or 1 nF.

Hi Klaas Mine have been in a draw for 30 years from the seller info but who knows ....So it sounds ok to run it how i have in the dark ..I will have a another read of Steve A PMT experiment ...sounds like i should give it a run for a week nonstop in it's little chamber/

I have a very low voltage power supply where i can adjust it 10 increments per volt i can bring a led up from zero to full slowly ..Steve A used a Blue Led instead of the UV so i will look for one ...

Thanks for the suggested procedure for the preamp and test i will do that .

Also on reducing the dark current i will have to work out a safe set up to run the pmt for a while and not forget ...Thanks again Klaas they should rename the PMT the light memory tube !

[Harry Dalek]

Today i adjusted the power supply for a closer 1000 volt voltage ,Scope reading last picture 2 volts per div ,i will give it a long nonstop run soon on so i can do the Led test .

ON the Blue led for the coming test i had a batch of 3 colour versions so replaced the UV with it .
First test of the led had them for a year or 2 never tried them till today ,i suppose its much easier to check how well or not so well this PMT reacts to the other wavelengths.....I will run these very low when i do the PMT test as Klaas mentioned ....If the tube works Led light should be invisible to the eye .

[Klaas Robers]

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.

[Harry Dalek]

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.

Ok Klaas I can do that ...i suppose i have to be careful here to ,an led to bright might not be a good thing for the tube .

I have no experience with these things apart from to date hate to brake it now ! have been reading the past PMT posts on the forum.

I was planning on running it on your advice for that 100 hours before i did a Led test ...if the tube is exposed to light after all this should it be given another long run for further work ? Steve was giving he's a day before retesting .