Hum in my Plexi 50w , need help

[gepposound]

I completed to build a Plexi 50w based on Metroamp kit layout .
I'm very happy with the sound , i used Pec Pots, Kiwame resistors, Sozo caps, Classic tone transformers, and nos preamp tubes..
The amp has very good clean tone , at full volume the tone is very warm but with a tight focused bass.
The only problem is that it hum without instrument at volume 0 .
After i found that problem i rewired the ground following the Larry ground scheme but the hum was still there.
If i use the return of the interrupt style loop with an external preamp i get NO HUM.
If i swap out the V1 tube there is HUM
if i swap out the V2 tube there is NO HUM.
When i turn up the volume on the normal channel without instrument at about 3/4 the hum goes away , if i turn the volume at full there is again hum.
When i turn up the volume on the treble channel the hum remain constant , there is only more hiss at full volume .
I checked the signal cable from the inputs to V1 and i didn't found any problem.
all the tubes are OK , all the voltages are OK.
I also checked all the connections between inputs jack and v2 and i have no found nothing wrong.
Im' thinking about the heater wiring ......any ideas ?

[stef]

My wild guess it's something related to Pec pots grounding, but post some pictures and someone will help you out

[gepposound]

The back of the PEC pot are not grounded , but i used the larry ground scheme...
I wired the tube socket with short wires coming from the high and there is no contact with the chassis.

[neikeel]

Sounds like a ground loop around the tone stack (or your lopp).

Have you tried splitting off the ground on your loop from the poutput jacks and running a dedicated ground to the chassis?

[stef]

I like alpha pots and stock grounding, wiring etc... Wide open amp, hot pickups, even slight boost in front and other analog time based effects pedals and zero problems with noise

[gepposound]

thanks , i will try to isolate the ground of the loop and find a different connection point in the chassis...
Do you also think the problem could be related to the fact that i didn't grounded the back of the PEC pots ?
If i rembember there are other layouts with the back of the PEC pots non grounded.

[neikeel]

thanks , i will try to isolate the ground of the loop and find a different connection point in the chassis...
Do you also think the problem could be related to the fact that i didn't grounded the back of the PEC pots ?
If i rembember there are other layouts with the back of the PEC pots non grounded.

Not an issue as long as the ground lugs are properly grounded (as per Larry grounding).

[Carbia]

take a crocodile wire (I don't know the exact english name, sorry, some help?), attach one end to the main ground in the chassis and plug the other end in the points of the circuit that should be connected to ground. It should help to identify some grounding issues.

[gepposound]

Thank you all , i will try your ideas.