Photomultiplier Tubes camera build

[Harry Dalek]

Today i have run the PMT for 7 hours so far every ting seem ok so the power supply has held up which is good .
I think i can start to see a reduction in noise i don't know if this is running the tube in reducing the dark current as wanted or particles it may be receiving from perhaps the sun , the sun is setting so i might be able to tell by tomorrow if this keeps on reducing or at sun rise i get an increase again.

Any way the scope shots are start up and during the times i checked how it was going .Scope on 2 volt per div not touched from set up .

[Harry Dalek]

Second day i can see a reduction in noise for sure seeing the tube scope shot at the start yesterday and end of today it is getting better....

came across this looking for data sheets for my other PMT's sounds like its better than nothing...

While Ive never had to do this myself, I understand a good digital capacitance meter will let you work out the dynode chain, wiring the dynodes together and exposing to dim indoor lighting and putting 20volts (harmless for a PMT) between either end and the dynode chain should tell you for certain which is the photocathode (current will be uA small).

Knowing which dynodes to put the variable resistor across to get the focus voltage is probably more of a dark art.

All my tubes came with either intact dividers or data sheets, they all seperate odd and even dynodes as well, which means the resistor string zig-zags over the base in a farmiliar way.

Not much help now I'm afraid, but then I think we all have a habit of taking the pulse off the wrong pin and turning up the supply voltage until it registors on the scope...... Don't we?

[Harry Dalek]

The RCA 6199 PMT has been running non stop for 100 hours at a touch under 1100 volts i noticed no real difference in the scope display over the last few days as in the first animated GIF showing the end of the each of the last 3 days .
So i was thinking it was time to give it a test .
Taking Klaas advice on the test i soldered a 100k resistor to the blue lead of my 3 colour LED hooked that led up to my low voltage power supply ...so bit of a quick test today i increased the voltage and it is sure detecting photons must be bugger all to the eye but this Photomultiplier is seeing it by the looks of it .

I haven't added the cap to the anode and ground yet to reduce noise ...i should of also started off at a lower voltage to PMT second thoughts .

OH well this is very promising results today .

[Klaas Robers]

Congratulations Harry, it looks as if you have successful finished a very delicate process. Write down the voltage on the LED-resistor combination that you applied for a decent increase of PMT output current. Then later, after you switched the PMT voltage off, you may open the enclosure and experience the light output of the blue LED at this setting. I bet that you have to make the room dark before you can see the tiny blue light output. PMTs are very sensitive. This is needed behind a Nipkov disc that has a "transparency" of less than 0.1%. Tis transparency number is normal for a 32 line disc.

Good luck with your further experiments. This is science.......

[Harry Dalek]

Congratulations Harry, it looks as if you have successful finished a very delicate process. Write down the voltage on the LED-resistor combination that you applied for a decent increase of PMT output current. Then later, after you switched the PMT voltage off, you may open the enclosure and experience the light output of the blue LED at this setting. I bet that you have to make the room dark before you can see the tiny blue light output. PMTs are very sensitive. This is needed behind a Nipkov disc that has a "transparency" of less than 0.1%. Tis transparency number is normal for a 32 line disc.

Good luck with your further experiments. This is science.......

OH thanks Klaas but big thanks to you there on the correct test procedure ! I had no idea ,i was thinking my low voltage power supply was good enough but the photomultiplier tubes are more sensitive than any thing i have ever tried i hate to think if i tried this without your suggested 100k resistor.
I didn't have any time this afternoon to try more today but will do tomorrow and coming days .
The good thing is i do have more of the 3 colour leds so i can do the viewing of one of these leds in a dark room without touching the PMTS one........as i recall it was a between 1.90 v and 2.00 volts on the power supplies meter but i will need to double check this .
Well i now know what to expect from these things ....
i would now like to see how the other colour leds go and a transmitting led would be interesting,in the past i have tried transmitting nbtv via a led to solar cells and light sensitive diodes and such input it to the computer using Garys software to view the video result .
I have been reading the old news letters in the hope one of my PMT's would work and how others have used them ,so yes a camera try would be something i would like to do .
Thanks again for the advice Klaas

[Klaas Robers]

Wow, if even with a 100k in series the applied voltage is no more than 2 volts, I would try a 1M in series. You can place that resistor directly from the low voltage power supply to one of the wires going to the LED inside the dark box. You even can place a second identical LED in series in this chain. Outside the box of course. Both LEDs will do the same, so you can see the effect of the current on the LED.

I would only be satisfied if the voltage that you apply to the series chain can be increased to about 5 to 10 volts with a reasonable response of the PMT tube. Then you know that the resistor is mainly responsible for the current and not the very non linear "resistance" of the LED diode(s).

Good luck, Klaas

[Harry Dalek]

Wow, if even with a 100k in series the applied voltage is no more than 2 volts, I would try a 1M in series. You can place that resistor directly from the low voltage power supply to one of the wires going to the LED inside the dark box. You even can place a second identical LED in series in this chain. Outside the box of course. Both LEDs will do the same, so you can see the effect of the current on the LED.

I would only be satisfied if the voltage that you apply to the series chain can be increased to about 5 to 10 volts with a reasonable response of the PMT tube. Then you know that the resistor is mainly responsible for the current and not the very non linear "resistance" of the LED diode(s).

Good luck, Klaas

OK Klaas i will give that a go .
This afternoon before i read this message i repeated the Blue colour led test and also tested the other 2 colours and also took some readings .
I checked my panel low voltage power supply meter against my multi meter its pretty much spot on .
Checked the 100k resistor in case my eyes were wrong on the colour code meter reading again spot on 100k//
I took the readings below and later i wanted to repeat it and discovered since its late afternoon shed light levels have dropped some how theres some light getting in to the tube i think since i replaced the led for testing the foil under the tape is torn and some photons are getting in ,with the levels dropped the Blue led has gone to the red led voltages detected by the PMT (more sensitive) !
...........................This was the first test below
Scope set on 2 volt div...and adjusting the voltage on my low voltage power supply checking the scope reading from the PMT preamp ....as it detects the light and then adjust to 6 scope divisions top of the scope and i took a reading of both .
Red led 1.40 to 1.70 volts
Green led 1.80 to 1.90 volts
Blue 2.10 to 2.15 volts
To me it shows me the tube is sensitive to blue end of the light wavelength but as you told me it is sensitive to the other colours just at a lower voltage and a slight higher voltage range from red to green to blue ///i would of thought before the test the range of the red and blue would be the other way around !
Should I of checked a scope reading on the anode before the preamp instead ?
Perhaps the PMT run at 1100 it makes it more sensitive it seems to drop of very quickly at lower voltages the power supply its not variable just selectable to a range of voltages ....so i cannot be to sure what is best to run it at ......at 1100 volts negative i know its very sensitive ,no wonder it would be damaged if exposed to day light .
Any case its a very fascinating thing the photomultiplier tube !

[Harry Dalek]

Today i just had another look at the Blue LED with Klaas procedure using a 1 meg resistor ...Tested this with another same led out side the PMT test you can see it top of my low voltage power supply range of 3.7 volts ..on a 5 volt supply its a touch brighter .

Testing this now with the PMT blue diode it can see the led at 1.64 volts much better than my eyes see scope low and high range shots below ! it peaks out on the scope at about 1.72 volts .

Since adding thr 1 meg resistor the bandwidth in the scope reading is now narrow ? as in looking at a pulse ...

What do you think klaas ? higher resistor ?

I put the pmt tube into another that fixed the light problem enough....and as you see power supply meter is supplying correct voltage.

[TaraByers]

The yellow output of white LEDs is generated from the UV excitation of a phosphor which can be quite slow in response time. Though the PMT shouldn't much respond to it, why throw another potential variable into the equation? White LEDs are marginal even for NBTV, they may get better with time but generally white LEDs are used in flashlights and other simple devices where human eyesight is involved - and that's not particularly fast.

[Harry Dalek]

The yellow output of white LEDs is generated from the UV excitation of a phosphor which can be quite slow in response time. Though the PMT shouldn't much respond to it, why throw another potential variable into the equation? White LEDs are marginal even for NBTV, they may get better with time but generally white LEDs are used in flashlights and other simple devices where human eyesight is involved - and that's not particularly fast.

Hi there Tara
OH i didn't use any white LEDs i was testing red green and blue from this tri colour LED ,i was at first not expecting the PMT to pick up the other colours at all ,in the data it says 30% either side of UV it really picks up all the colours ,with red there is a wider range in voltage slight as it really is before the pmt peaks takes less so on Blue and green is in between the two ...i could see perhaps a colour wheel used with one of these things if you were that way inclined for a colour camera.

So the colour tests where done as i was interested since Klaas mentioned it could pick that up ...and i had the 3 colour led handy to check ...i was going to start off with a UV But Steve A said it would be wise to go with Blue ,glad i swapped to the 3 colour to see .

I am looking into modulating one of the Leds in the test tube chamber now and see a waveform ,i will be using a Steve Andersons reversing wave and a little one transistor circuit to modulated the led ...just finished a copy of one i made a year or two back for the same sort of idea to transmit modulated light to a solar cell hope to test that tomorrow .

[Harry Dalek]

I finished remaking the old led light modulating circuit and testing it out on the PMT ,i made a dual version might use it for some thing else after i am done with it for this on testing colour leds .

Top trace is taken at the Led thats being modulated .
Bottom out the preamp.

Any case today i tested it out on all 3 colour LEDS with Steve Andersons reversing wav... seems to work better on the Red LED then go's down hill on the GREEN and worse still on the Blue...
i am not sure the colour transmitting the video has any thing to do with it more than my circuit driving the led or the properties of the led its self ....I will have a look what Steve used in he's test .
I have also not yet used a noise reducing capacitor as klaas suggested at the PMT anode to ground i will give that a go too next .

[Klaas Robers]

Harry, you have not placed a high ohmic resistor in series with the LED. 1k is not high ohmic. What you are seeing is the non linear characteristic of the LED diodes, because you are driving the LEDs by a voltage, not by a current.

When you drive the LED by a current, then the output staircase will be just like the input staircase. However most NBTV LED-driver circuits have gamma-correction, which is non linear itself. For these experiments you want to have a linear circuit, so don't use a standard NBTV LED-driver.

[Harry Dalek]

HI Klass

Harry, you have not placed a high ohmic resistor in series with the LED. 1k is not high ohmic. What you are seeing is the non linear characteristic of the LED diodes, because you are driving the LEDs by a voltage, not by a current.

The 1k was just for the no board led i forgot to mention i had a a 100k resistor and the chamber TRI colour LED in series ,i will try a larger resistor 1 meg again

When you drive the LED by a current, then the output staircase will be just like the input staircase. However most NBTV LED-driver circuits have gamma-correction, which is non linear itself. For these experiments you want to have a linear circuit, so don't use a standard NBTV LED-driver.

...

I will look into this read up and try Klass ,thanks for pointing the way .

[Harry Dalek]

Looking into playing around with a standard Nipkow 32 line for a start with this PMT.....taken me ages to think about how i was going to house the nipkow lens and such .
Well all i can do is try and see.
Doing some experiments with different lenses i found the 35mm gave to large a image on a focused screen ,i tried some old video camera lenses and they gave just the right small image size for a 32 line nipkow and you can adjust via zoom to act like adjustable mask so the nipkow holes show one at a time so this came in handy as well....so went with the ugly video camera version .
If i have got it right the lens will focus a image to nipkow , ..... behind nipkow photomultiplier ...i read in a past newsletter some one had a mask and screen between the nipkow and PMT ...which seems to me to be a bit like a monitor light diffuser but instead a little projection screen ....it was also mentioned the sensitivity of the pmt was adjusted moving it towards and away from the little screen ...close up tiny flying spot scanner i suppose ,so a few ideas to play around with .
Today mounted the lens on a little 25 i think CD or DVD drum holder which i will have to light proof with matte black paint it ,the Nipkow and CD motors lets me just clip on and off the cd nipkow which i mounted in the drum wrong way around just for showing
So this is the concept of sorts in the last picture the tube with photomultiplier mock up ..so far ! things could change .

[Harry Dalek]

Finished painted the drum inside black yesterday and remounted the lens and today worked on the problem of mounting the motor that drives the Nipkow .
I could of tried to cut and adjust the center cd column to mount the motor on but i was thinking this might be a problem if i am out a mm or so, so came up with this idea to adjust the height of the motor to hopefully the focal point.
Theres not much room and very tight but could be worth it.
On to the photos ....
First few photos i am using to work out focus to the Nipkow replaced the disc with a clear version with a tiny screen .
Then on to the problem of mounting the motor and what i have come up with ,with what i had at handy .
Need to test that then see how to mount the PMT.
I will rename this Subject to camera build as looks like its heading that way .