Dsl 100 Preamp hum

[abav]

Good Afternoon everyone. I have a dsl 100 in for service with a single coil type hum on both channels. Checked effects loop.... its only on preamp side. without an instrument plugged in...quiet as a mouse. Distortion is good on both channels and voltages are fine. I have tried different guitars to rule out the customers instrument to no avail. Even with humbucker pickups...still there...and it is loud enough to be annoying on stage.
I checked the pop-rivot grounding points..all seem tight. I also Pulled the preamp board and checked for bad solder joints....There were a few..but didnt change anything. What am i missing?? It still seems like a grounding issue to me....(like a guitar cord left unplugged).
Any help would be appreciated.

Art

[guitician]

Have you ruled out the pre-amp tubes? Maybe a dirty jack? You could do a trace of the circuit looking for the source. Use a ground lead with a probe point and ground out all the AC signal points untill you find the right one.

[abav]

Thank you for your quick reply. Yes, i have changed tubes....Cleaned and checked the jack, The hum originates at v1....i am going to check those wonderful connectors, and go from there.
Thank you for your time....

Art

[tim]

so what you're saying is if you pull V1 out, hum goes away?

[abav]

Sorry i didnt get back sooner tim....had a family thing down in florida. To answer your question...yes when v1 is pulled hum goes away.