Crack Hum (Solved)

[Subscript]

I have a quiet hum going on in my crack. Sometimes it rings a bit if I tap the unit somewhere. I've retouched all the solder connections, redone my braid and twists, tightened screws on the power supply, cleaned the tube connectors and had it running for about 50 hours. I've also tried in a more isolated room with shorted jacks. I'm running HD650s.

The only voltages that seem out to lunch are A1 and B4 which are coming up at 74.3. Which isn't even that far off. A6 and B1 are around 79.  Also, A1 and A7 are giving me 1.5-1.6V.

I also have a faulty power switch, at least it doesn't do anything but still looks connected properly. I'm not sure how that would affect the hum though. I haven't e-mailed for a new switch since I wanted to make sure I had the rest working first.

Any advice is appreciated!

[Doc B.]

If the hum is soft and deep it might be time to try a different 6080. If it is buzzy you probably have a ground connection that needs to be touched up.

[Paul Birkeland]

What headphones are you using?  Does the soft hum vary when you move the volume control?

[Subscript]

The hum is soft, but I wouldn't say deep. Is there specific terminals I can look for ground connections or is it just the black wires? Also does the is the sound when tapping the sides indicative of anything?

After about the 50% mark on the volume a static like sound comes in that seems separate from the hum, but I'm guessing that's normal and way too loud for anything anyway. Otherwise the volume doesn't really affect it. I'm using Sennheiser HD 650s.

Thanks for the help!

[Paul Birkeland]

The tapping is tube microphonics, which is almost certainly separate from your issue.  I would actually suggest replacing the power switch. 

-PB

[Subscript]

Solved

I replaced the tube and silence now graces my ears. The sound is wonderful and I can't wait to add my speedball.

I e-mailed the replacement parts email for a new switch.