Is this a good GM tube voltage regulator and rectifier?

[eigenmax]

https://www.circuit-diagram.org/editor/
Hi, I was wondering if this is a good voltage rectifier and regulator for a GM tube power supply? The AC supply is approximately 500V, and the strange component at the bottom is a voltage regulator tube. Seems to work OK but I don't have any test equipment to verify this, and am wondering if anyone would be able to say if this works.
Thanks

 

[Borek]

You linked to an editor which opens an empty project, not a circuit you think it does.

 

[eigenmax]

Sorry, I'll fix that now. file:///Users/johnodonoghue/Downloads/circuit.svg does this work better?

 

[anorlunda]

Sorry, I'll fix that now. file:///Users/johnodonoghue/Downloads/circuit.svg does this work better?

I don't speak for everyone, but I would never download a file from a stranger and open it. Too much chance of malware.

If you want to improve your chances for getting an answer, take a screen shot of the circuit schematic, then post it here using the UPLOAD button below next to POST and PREVIEW

 

[Borek]

Sorry, I'll fix that now. file:///Users/johnodonoghue/Downloads/circuit.svg does this work better?

No, that's just a local link to a file on your computer. As arnolunda already pointed out, svg is not an image format that is considered safe. Export the circuit to a gif or png image (best) or jpg (bit worse) and attach it to your post. If you can't export it, just saving a cropped screenshot will do.

 

[eigenmax]

Sorry about this, I haven't got much computer knowledge. Will this work?

 

[gleem]

There is one symbol that I am not familiar with, it is the unlabeled square in series with the AC source. What is the 500 VAC source. This is very irregular for any GM counter which I am familiar

 

[davenn]

Sorry about this, I haven't got much computer knowledge. Will this work?

There is one symbol that I am not familiar with, it is the unlabeled square in series with the AC source. What is the 500 VAC source. This is very irregular for any GM counter which I am familiar

and there is no other circuit connection to the GM tube ... the circuit as it stands will not work !

 

[davenn]

There are a zillion Geiger counter ccts on the net

https://www.bing.com/images/search?q=Geiger+counter+circuit&FORM=HDRSC2

Am sure most of them probably work well

trying to find one that is similar to my one which runs off a couple of 1.5V AA batteries ... if I find, I will postDave

 

[davenn]

Amongst that list I found this one which is almost identical to my counter

this pic below shows the type of Geiger tube my unit uses ( this IS NOT my or the above circuit)

Dave

 

[eigenmax]

The square component is a voltage regulator tube. The pulses are taken from the free end of the capacitor and the tube cathode (shell) to the amplifier (not shown).

 

[Baluncore]

Attach a common ground return to the GM tube. Pulse output labelled.
What is operating voltage across the gas discharge tube? Maybe between 90 and 150 volts?

Maybe reduce the 1M ohm resistor to 100k to get sharper separated pulses from GM tube.
I think you should have a small reservoir capacitor, cap, somewhere across the half wave rectified supply.
You should not need a 500V AC supply. You could probably reduce that to 200Vpp, which will lengthen the life of regulator components.

 

[Tom.G]

Aren't the 10k and 1M swapped here?

 

[Baluncore]

Aren't the 10k and 1M swapped here?

That is quite possible. It will have signal amplitude, quenching and dead time implications.

I am suspicious of this circuit because the AC rectifier and regulator are inefficient and appear not to be optimised. It seems to be one arrangement of available components that might somehow work. We have no idea who designed this circuit, who modified it, or if it is correctly drawn.

 

[gleem]

Aren't the 10k and 1M swapped here?

Actually I do not see the need for them at all the pulses are very small and wouldn't they increase the time constant of the output pulse ? Another point the gas discharge tube fixes the voltage (90V - 150V ? ) to the GM tube which maybe a little low for many(most?) GM tubes.

I still cannot figure out why the use of a HV AC source.

 

[Tom.G]

(referring to the 10k and 1M resistors)

Actually I do not see the need for them at all the pulses are very small...

Try looking at it this way @gleem, the voltage source is rather 'stiff', i.e it is low impedance... or put another way, especially with the Voltage Regulator helping, it will hold a constant output voltage over a significant range of current. When the GM tube detects a particle there is a short-lived, high resistance conductive ion path between its electrodes. The tiny amount of current that flows thru the ion path is very small. If the GM tube were connected directly to the low impedance voltage source, there would be essentially no change in the voltage, meaning there would be no signal.

Now if that tiny current from the GM tube has to flow thru a resistor ( 10k + 1M in this case), according to Ohms law (V=I×R) there wil be a voltage drop across the resistor. That voltage drop is what is fed to the amplifier stage.

The reason I suggested that the resistors are swapped is that most of that voltage drop will be across the 1M resistor. In fact with those resistor values 99% of the voltage will be across the 1M resistor, with only 1% left as signal the the amplifier. With the resistors swapped yoou get a signal 99 times as high to send to the amplifier. (a free gain of 99 just by swapping the resistors)

Hope this helps.

Cheers,
Tom

 

[gleem]

It is not clear to me that the voltage regulators has a low impedance for the pulse generated in the GM tube. The gas discharge tube probably has a substantial impedance as well as the choke. The capacitor between the two resistors has little impedance for the pulse and passes it to the output .and acts as a coupling cap to an amp while blocking the high voltage.. The circuit in the OP is obviously incomplete but the output would be connect to an amp with a high resistance input. If the regulator is low impedance then yes you need a high resistance between the cap and the regulator but I do not see that you need any resistor between the cap and the GM tube although it does not hurt.

 

[Baluncore]

but I do not see that you need any resistor between the cap and the GM tube although it does not hurt.

I think the GM tube series resistor is there to prevent continued secondary avalanche, to quench the tube after a pulse.
The design of the amplifier employed will determine signal load impedance and susceptibility to power supply noise.
The implications of the flyback diode across the huge 100mH choke are interesting when it comes to signal pulses and discharge tube noise peaks.
Again, we don't know where this circuit comes from. Arguing the purpose of components based on an unreliable diagram of an irrational design is pointless.

 

[gleem]

One final remark seems appropriate to me. The regulation of the GM voltage is not critical since the voltage of the pulse does not change very much in the region of voltage operation and that the precise pulse height is not of concern anyway.