Valve stage coupling capacitor leakage?

b1o2r3i4s5 · 26th February 2012, 07:35 AM

I've constructed a simple 2-stage valve preamp (voltage gain and cathode follower).

Each of the stage works fine independently, but once i put the stages together with a capacitor the cathode follower's bias voltage changes and puts it in cut-off state.

Im suspecting that its caused by the coupling capacitor's leakage but i can't be sure, I'm currently using a 250V Metalized P.E. cap.

If it is caused by the leakage, then how do i solve it, if not then what other causes could there be?

SY · 26th February 2012, 10:20 AM

A schematic would help. If you have photos, that would also be nice (it COULD be as simple as a wiring error).

DF96 · 26th February 2012, 12:26 PM

Coupling capacitor leakage almost always turns the next valve on too hard, not off. My guess is that you have a circuit or wiring fault. A diagram would help.

26th February 2012, 07:35 AM	#1
b1o2r3i4s5 diyAudio Member Join Date: Feb 2012 Location: HK	Valve stage coupling capacitor leakage? I've constructed a simple 2-stage valve preamp (voltage gain and cathode follower). Each of the stage works fine independently, but once i put the stages together with a capacitor the cathode follower's bias voltage changes and puts it in cut-off state. Im suspecting that its caused by the coupling capacitor's leakage but i can't be sure, I'm currently using a 250V Metalized P.E. cap. If it is caused by the leakage, then how do i solve it, if not then what other causes could there be?

26th February 2012, 10:20 AM	#2
SY diyAudio Moderator Join Date: Oct 2002 Location: Chicagoland Blog Entries: 1	A schematic would help. If you have photos, that would also be nice (it COULD be as simple as a wiring error). __________________ If there's a sucker born every minute, where do the rest of them come from?

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26th February 2012, 12:26 PM	#3
DF96 diyAudio Member Join Date: May 2007	Coupling capacitor leakage almost always turns the next valve on too hard, not off. My guess is that you have a circuit or wiring fault. A diagram would help.