Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: hylaphone on October 13, 2025, 01:07:30 pm
-
Hi folks, I have a HRD here with ongoing static noise issues. I've isolated it to V2, seeing between 1 and 2VDC on both grids of the tube. There is also <1VDC on the TMB pots. Leaky tonestack cap would explain DC readings on pin 2 but I'm having a hard time visualizing what would cause the same on pin 7 as it's not present at the C2/R18 juncture.Trying to wrap my head around this before pulling the PCBThank you!https://el34world.com/charts/Schematics/files/Fender/Fender_hotrod_deluxe.pdf (https://el34world.com/charts/Schematics/files/Fender/Fender_hotrod_deluxe.pdf)
-
Before pulling the PCB have you tried with another 12AX7.
-
Before pulling the PCB have you tried with another 12AX7.
Yes, no change
-
Do you get grid DC with no tube present?
How about if you remove power to the relays?
The way I see it is you either have a leaky tube, leaky relay, or conductive board.
-
Do you get grid DC with no tube present?
How about if you remove power to the relays?
The way I see it is you either have a leaky tube, leaky relay, or conductive board.
Good call, I pulled the connectors from the bias and +/-16V supply, and the DC was still there.Removed the ribbon cable at that tube and found several hundred Kohms continuity between plate and grid pins - BINGOTook a few tries to clean and resolder that cable but it did the trick.Thank you for the help!