Hum on left channel (solved -- Thx Doc!)

[Bacci]

Hello

I just soldered my Crack and after all checks it works nicely.
The only issue is humming in the left channel, independent of volume and input.
I tried reflowing the joints where the output caps are, as well as plugging/unplugging the tubes a couple of times but no difference.

EDIT: The hum kicks in after about 5-10 seconds, when the tubes are warmed up. Tried reflowing all connections, no dice. Tried swapping out the 12AU7 with a 12AT7 I had lying around, no change (except for gain, of course). Tried cleaning the 6080's feet, also to no avail.

Very occasionally the hum goes away a little bit (after some space-ee sounds) but then comes back.
It's like listening to music while the hairdresser is giving your sideburns a trim.

Any ideas?

Thanks
B

 

[Doc B]

If it is an oscillation (that's what it sounds like based upon your description) it might be that putting some contact cleaner on the tube pins and into the socket holes (just a wee bit) will help. Reflowing the pins of the tube sockets might help too.

 

[Bacci]

Just scrubbing the tube's pins with a dry scotch brite wasn't enough.
Contact cleaner, both a little in the socket and on the tube's pins, did the trick though!
Will now enjoy the stock crack for a while before mounting the speedball.

Thanks Doc!

 

[Bacci]

Just want to add that the 6080 tube included in the package remained a bit noisy, even after cleaning with dremel, cue tips and contact cleaner. There is still a tiny bit of buzz left on both channels. After inserting an AS7G I got from a reputable British vendor the noise floor went down to near zero, lifting the Crack to new joy levels.
I guess those boxes of NOS tubes are like boxes of chocolate