small voltage at grids 1 and 2...help!

[swt]

HI!. After working for a long time in this amp, and searching for a hum issue, i realised that i have a small voltage at the grids of tube 1. What can be the cause of this? How can i trace it?. Voltage at input jack is zero, but at grid 1 is 7mv. And the real problem is at grid 2. i have 60mv, and if i disconnect the whole eq and leave just the volume, with gain at zero i have no voltage, with gain maxed, i have 160mv. I also took out the neg feedback. there's only the 220k and bypass cap at that stage's input, and of course the gain pot. I've changed tubes, and the problem persists. Any clues?.
Also...when i touch the chassis anywhere the hum seems to be the same, but if i touch it near the first preamp tube, it disappears...
All preamp tubes use dc filament supply, reference to ground as in tut books.
Thanks a lot for your help and consideration...
Ps: it's a d*mble clone type of amp...

[Ray Ivers]

swt,

Try disconnecting your heater supply (both wires). The tubes will still remain hot enough to function for a few seconds, which is more than enough time to eliminate the heater supply as the hum problem - if it is, the hum will vanish the instant you disconnect it, and if not, the hum will remain and gradually fade away. If you have a 6V lantern battery, you can use it to power the preamp heaters for troubleshooting as well.

Ray

[swt]

well Ray...thanks a lot! that's a good tip. you know...the voltage issue was a whole batch of EH tubes. Put a sovtek in there, and problem solved. I'll keep on searching the hum and hiss issue, as it's there anyways...thanks again.