Quiet high pitch and hum in right channel

[junkimchi]

Just finished building my Crack! Looks and sounds amazing so far but there is a very small issue that is bothering me. When there is nothing playing, there is a very quiet, low pitch hum only in the right channel. On a scale of 1-10, I would consider the hum to be about a 0.5 so its very quiet.
Some additional details and observations:

- unplugging the RCA cables do not have any effect on the hum
- turning/changing the volume has no effect on the hum
- when the amp is first turned on, hum is not there but a very deep pitch sweep happens about 5 seconds then the hum begin with an occasional high pitch

EDIT: This might sound kind of crazy but I can hear the exact pitch even WITHOUT my headphones on. As in if I get really close to the amp, I can hear the pitch around the power tube/transformer area. Seems to have lessened the longer I leave it on. I will keep everyone updated lulul

 

[sjeffrey]

Try tapping lightly with a pencil on each tube and see if it affects the hum.

 

[Paul Birkeland]

I'd start by carefully reheating all your solder joints. 

Also, examine the twisted pair of wires snaking from tube-to-tube.  How tightly bound is your twisted pair?  How close to the chassis plate is it? 

 

[junkimchi]

I would have to say that tapping the power tube change the hum and at one point got rid of it for a second

I would say that my twist is pretty tight. Its very close to the plate also:

 

[Grainger49]

I have posted this before.  Hum can be from ground.  Here is the path to rewet all ground terminals/pins for the Crack:

The start of the grounding points is terminal 3.  This jumps to the 2 left lugs of the volume pot and back from there to the RCA jacks.  From the top left lug of the volume pot there is a grounding jumper to the two bottom lugs of the headphone jack.  This jack may be different than what is being delivered today.

Also from terminal 3 you go to the center lug of the 9 pin tube socket.  This is the ground route for the LEDs in the cathode circuits.

The power supply ground comes from those bottom headphone jack terminals to terminal 12.  From there it jumpers to terminal 14 and ends at terminal 20.

The heater (AC) supply is a ground wire from transformer terminal 4 to terminal 22.

Ok, so all this means you should clip on to the chassis (which is screwed to terminal 3 the source of all the grounds).  Tracing from the plate outward you should read zero to T3, Volume 2 left lugs, both RCA outer conductors, headphone jack bottom terminals, T12, T14, T20, center pin of the 9 pin socket, and to T22.

Other grounds that should be solid are pin 8 of the large tube, pin 4 and 5 of the small tube, T8, T11, T14, T16, T17, T20, T21 & T22.

 

[junkimchi]

Not sure if at this point I would even consider it a hum. I will try the new tube next week and if that doesn't solve it, try reflowing the joints and follow your grounding advice. Thanks again!

 

[junkimchi]

I switched out the output (bigger) tube and the noise is gone!

Is there any way to get a replacement tube if I pay a bit of shipping or something!