Definite 60hz hum from brand new, stock Crack

[hogarthd]

I just finished a totally stock Crack amp about 2 hours ago.  I'm listening with Sennheiser HD650s.  The amp makes a very definite 60hz hum - it doesn't matter if/what the source is, it will hum when nothing is connected.  When first powered on, it is totally silent, but the hum softly fades in after a few seconds when the tubes start to glow. The volume knob doesn't change the volume of the hum.  It is definitely 60z (after listening to both 60 and 120hz tones for comparison). I can tell this amp sounds great, but it's virtually un-listenable with this humming sound :/

I've never built anything like this before, but I am decent at soldering from lots of miscellaneous R/C airplane stuff over the years.  I was very careful to solder (and occasionally re-solder) all the joints really well.  The resistances and voltages all checked out perfect the first time checked them so it seems like things are OK, technically speaking.

I'm up in the Seattle area, I could easily bring it by the Bottlehead HQ for a check up

Any ideas anyone?

thanks!

Hogarth de la Plante
Kenmore, WA

 

[Paul Birkeland]

Sure, feel free to bring it by! (Though we may be out of the office on Wednesday).

-PB

 

[hogarthd]

I re-flowed all the solder joints and rechecked all the resistances and voltages - everything checks out perfectly but no fix, I can still hear the 60hz hum. I've noticed that the hum is only in the left channel, though, so maybe that helps in troubleshooting a bit. Again, the hum does not attenuate with the volume pot, does not matter what the source is (there can be no source and it still hums) and I've tried moving the amp to different parts of the house/different outlets.

Anyone think this might be a bad tube? 

 

[Doc B]

Yeah, could be a tube issue.

 

[hogarthd]

Fixed!

It was the 6080 tube.  I replaced it with a cheap, Sylvania 6080 NOS that I got on eBay and it's dead silent now!