Hoffman Deluxe Reverb build -- Reverb channel hum

[acheld]

I've built a Hoffman Deluxe Reverb, stock, and need some help trouble shooting some symptoms before I tear it apart and start over.  The problem is a 120Hz hum in the reverb section. 

1.  Normal channel works fine, and is silent.
2.  Reverb channel sounds good when reverb pot is turned to its lowest setting.
3.  Tremolo works as expected.
4.  When the Reverb knob is turned up past "1", there is a 120Hz hum present, becoming louder as the knob is turned up. 
     a.  The volume control for that channel has no effect on this hum.
     b.  Reverb works.  I can't say I like it, but I can't describe it well, it's just kind of vague.
     c.  When chopsticking V4, V4a is quiet.  V4b (pins 6, 7, 8) are microphonic when probed. Reflowing the connections and replacing the tube (x2) -- made no difference.
     d.  When chopsticking the input (wire to pin 7, the screen) to this section, when I move the chopstick along the wire, it makes strange ticking noises.  There are no visible defects in this Teflon stranded wire.

I can add more details as needed. 

Should I just tear out that section and rebuild?  Or are there other diagnostic moves I can make.

Chris

[shooter]

2.  Reverb channel sounds good when reverb pot is turned to its lowest setting

that tells me 9/10 it's a grounding issue, most likely with the tank n cables picking up stray 120hz.
not sure if jacks are isolation type, or should be
bad shielding
bad wire dress
F/S n wire, can test with gator clip or toggle switch
etc

[acheld]

OK, will go to work on the grounding.  Which is not up to the standards of this forum.

The RCA jacks are Switchcraft 3501 chassis mount, the ground is NOT isolated from the chassis (if that's what you mean). I wondered about that when building . . .

What is: "F/S n wire"?

[shooter]

foot switch (F/S)
the long cable is a GREAT place for junk to get picked up and added to the mix

[acheld]

I redesigned the grounding scheme, and that has solved the reverb hum issue.

Original implementation was that the power amp and the pre-amp shared grounding, along with the reverb and trem RCA connectors.   Once the pre-amp and power amp grounding points were separated, and the reverb RCA jacks are left grounded to the chassis, the hum disappeared.  Thanks Shooter.

The F/S cable, despite being long, did not affect the hum.

The solder connections to V4b remain microphonic despite reflowing, and changing the tube twice.  Interestingly, one of the three tubes I tried (not the original) did make the microphonics worse.

Maybe I'm overanalyzing this.  Do ya think? 

[shooter]

Glad ya nailed it!

remain microphonic despite reflowing

try re-tensioning the pin holders, I've had to replace sockets that just won't behave
ALWAYS with a good belden