Preamp modification

[EeeTee]

Ok, first silly preamp question.. What's to stop me from converting a unity gain scintillator preamp into one with sufficient gain for a proportional counter tube? I'm aware of the need for super smooth soldering and making sure components are sufficiently well spaced on the HV side to prevent arcing- other than that the gain increase should just be changing out a couple of resistors around op-amps as far as I can see schematically. Is there something glaring that I'm not taking into account here?

Cheers!

[Sesselmann]

Teyen,

There is no such thing as a silly question, however I don't think you have provided enough information for a solid answer.

Technically no reason why you could not change a unity preamp to one with gain, but it would heavily depend on the circuit design.

Maybe some circuit diagrams or pictures would help.

Steven

[EeeTee]

Sadly no in-depth circuit diagram / manual is available (as is the case for most things made by Tennelec), so this is about as good as it gets right now!:

schematically it's the same as this, though:

cktblock.png (15.44 KiB) Viewed 15462 times

[Sesselmann]

Teyen,

It looks like a pretty old board, you might be better off making a new board and using the old enclosure.

For a proportional counter you want a high value load resistor, maybe 10M ohm to 50M ohm and a small coupling cap to give you a time constant between 20 to 50 µs., the shorter you make the pulse the taller it becomes, as the energy is distributed across a shorter time.

Follow that with a fast rail to rail opamp and make the gain adjustable, and if you are planning to use a sound card MCA you should stretch the pulse back out to 100 µs post amplification.

Good luck..

Steven