Strange coupling capacitor problem

[shzmm]

Hello,
I am having fits trying to figure this one out. Basically what I have is that the .47/400V coupling capacitor from a triode strapped el84 going to the input on a reverb tank is leaking DC. I've built the circuit before so I know it works.
When I place the voltmeter from ground to the outside leg of the cap it reads around 150VDC on startup then goes gradually down to around 2-3VDC. Strangely enough, sometimes I also read a negative voltage.
Obviously capactiors aren't supposed to pass DC and therefore it should just be a bad cap right? I have changed out the cap now 5 times with known good new ones. Perhaps there is something going on which is immediately destroying the caps? Anyways, in addition I have replaced the socket; disconnected all power supply connections save this one; replaced the main filter cap; changed all components leading to the tube.
As well it's a new transformer although this and something to do with the chassis and tag strips seem to be the only possibilities left I can think of...

Any help would be greatly appreciated.

[Robert M. Martinelli]

Hi,
Have you checked the 5 capacitors you subbed after replacing them? Once you've discharged them, you should read "infinite" with an Ohmmeter ( or a certain resistance in case they're leaky ), or, better yet, a capacitance meter would tell you if they're still good (and on-spec) or not. I don't think 5 capacitors rated at 400V can ALL go bad with only 150VDC across them, so either they already were defective before installing them, or they're not "true" 400V....or....could it be they're good and something is wrong with your meter....or with its settings? No disrespect intended, but I think that setting the meter in a wrong way ( or misreading it ) is something that's happened to all of us at least once in our life.

Hope this helps

Best regards

Bob

[Enzo]

I bet when you connect the cap to wherever it is supposed to go, that DC disappears.

I think you are misinterpreting the meter.

Your meter has a really high input impedance. When you connect a cap to B+ and have the other end hanging, and then put your meter to it, then it charges itself through your meter. Due to the very high meter impedance, it takes a little while to charge.

[shzmm]

Ah damn, once again I feel completely stupid. Yes you are right Enzo. Once connected the capacitor reacts normally. The problem started with a hum in the reverb tank and spiralled out of control. I really appreciate your wisdom and willingness to share your experience!