Hum Troubleshooting on My Tubelab SE with 2A3

[Doc Jr 8156]

I am trying to troubleshoot the hum on my Tubelab SE amp. My amp runs on 2A3s mounted on a Hammond aluminum case (16x 10). The opts are Electraprint, Hammond 370hx for power, Hammond 193j for choke and 50uf ASC caps parallel to C5. I followed the same grounding technique prescribed for the Simple SE. This is my 3rd Tubelab amp (2 SSE) and the only one that hums. The hum is independent of the volume and present even though the inputs are shorted. Can someone outline their grounding scheme on their Tubelab SE amp? Anyone here running 2A3s on their Tubelab SE amp? Thanks a lot and your help is much appreciated. Godspeed.

John Revilla

[Doc Jr 8156]

No takers? To compund the problem, I can only hear hum with signal input in place. No music, just hum.

My checkout voltage are all fine, B+ is 295 (Hammond 370hx), bias set at 54.5ma per tube, the 5842s are on 175 volts.

I'm using L4 and R4 as (+) inputs and L5 and R5 (-) for the
grounds on the RCAs.

Grounding scheme is as follows:

From the IEC a wire is connected to a ground lug, this lug is isolated from the chassis. Ground wires were ran from the common speaker outputs (black), RCA (right) ground tab to the ground lug. Another wire is run from the RCA ground tab connected to the mounting bolt of the OPT. This OPT ground wire is the only connection to the chassis. Both RCAs and speaker binding post were isolated to the chassis.

Can anyone help? Please..........

Godspeed.

John Revilla

[SigloOne]

Isn't the outer part of the RCA receptacle supposed to be grounded to the chassis?