12ax7 tubes- pre amp audio trace question

[newperson]

Hi,

Where would I find a simple drawing how a set of 12ax7 tubes work in a preamp?  I have an old Tel Ray (oil can) delay unit that I cannot find a schematic to.  I replaced all the caps and it worked fine.  Then on the last can/mulitcap I had to replace with three different ones to make the mulicap.  It never worked again.  I think I have wired something wrong, pulled something loose or blown a part, but I have no idea how to trace the signal once it enters into the tube.  There is no sound coming through the unit at this point, but it does still run and will produce an effect when certain resistors are touched.  I know about the volts/amps, and I am careful what I poke at.  I have tried to put in another set of tubes with no luck. 

There is one strange part in the unit.  It looks like a light bulb with two thick metal with no connector.  What could this part be doing? 

I have made an audio probe and can follow the sound around.  How should a basic preamp work?
I thought that this would be a good chance to learn how the audio path actually works. 

Thanks for any help with my problem.
-Paul.

[A.S.P.]

information lost...

[newperson]

Yes, I have checked out that page.  It has a lot of infomation, just not on my model.  I guess I might have to give in and take it to someone.  I would still like to know how a basic 12ax7 preamp works even if I take it to someone.  Would  a small Fender amp, say a tweed Champ, be an average preamp section?

Thanks for the link,
Paul.

[aron]

Paul, you can check out this link and see if it helps you.

http://www.diystompboxes.com/pedals/tubedummy.html