5E3 DC on .02 PI coupling cap?

[angelodp]

Hi, have a narrow panel 5E3 amp that is passing DC on the .02 coupling cap to the PI. Have swapped in a new cap and still have DC? Have swapped 12ax7 tubes no help. All the resistors around that circuit are in spec. Not sure how that DC is getting through that cap? Any guidance appreciated.

A

[sluckey]

Hi, have a narrow panel 5E3 amp that is passing DC on the .02 coupling cap to the PI. Have swapped in a new cap and still have DC? Have swapped 12ax7 tubes no help. All the resistors around that circuit are in spec. Not sure how that DC is getting through that cap? Any guidance appreciated.

That dcv is not coming through the coupling cap. It's coming through that 1M connected to the cathode circuit.

Don't worry. It's all good.

[angelodp]

Thank you sir.

A

[angelodp]

Steve, on this same 5E3, it plays nicely, but when you remove the guitar cable and crank the volume it goes into a screechy oscillation, that goes away once a guitar cable is added to the amp?

A

[sluckey]

Most likely a wiring error on the input jacks.

[angelodp]

Looking through it with a fine tooth comb.

[angelodp]

Input jacks are correctly wired. The amp (when no cable is connected), if you crank up the two volumes, will go into a screechy oscillation. I have looked at lead dress and checked for DC leakage. Limiter shows no shorts. The amp has been re-capped throughout by a fellow at Div 13 some years ago. Rob R has a voltage chart, I'll post where I am at with current voltage levels and some pics.

[LOUDthud]

Check that those input jacks ground the signal when they are supposed to.

[sluckey]

Show us your schematic if different from the stock 5E3. Also some high rez pics that show your 4 input jacks wired to the 12AY7 could be helpful.

With nothing plugged into any of the four input jacks, you should measure about 34K between pin 2 and chassis and pin 7 and chassis. What are your actual readings?

[angelodp]

Crud on the Jacks. So it was the jacks, although they are correctly wired, there had developed a cold solder. I rebuilt the jacks and its working correctly. Thanks for the support and intel.

Best A

[angelodp]

the Amp.... now Stone Quiet and sounds damn good