Tip: Hum in Fender Vibroverb 63 RI / Vibrolux CST

[Makita]

Hey there!

Thought I'd share something that I didn't find on any other tube amp related board on the web.

The 90s Vibrolux Custom + his brother, the Vibroverb 63 RI have a hum issue that is due to Fenders factory grounding scheme.

The pcb under the dog house has two ground wires attached, connectors are called CP 37 and 38 on the main board.

Though there is two wires, Fender chose to connect the ground from all capacitors. Split the ground of node Z and Y on the pcb under the dog house and it will reduce the hum in the amp drastically.

I have done this to a Vibrolux where the hum occured in V2, for a Vibroverb there was hum induced in V6 (PI). Both times, separating the ground has helped.

Thought I'd share. This forum has been a great resource for me over the years. Thanks to everyone and God bless!
Georg