Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Wanabejimi on September 13, 2020, 09:21:47 am

Title: Rail Voltage on Grids
Post by: Wanabejimi on September 13, 2020, 09:21:47 am

Greetings,  It has been a while since I've been here.  It's been a while since I've built an amp.  I'm in the start up process of a Princeton Reverb build.  The only modification is that this one will run 6l6's.  I've got the amp hooked up to a variac with the output set around 30 vac.  I've been going through the start up process.  I had checked the bias voltage already coming off the bias circuit and it was fine at around -6 VDC.  I took the amp off of standby and I've got rail voltage on both power tube grids (94 volts with the variac).  I've traced everything I can see and checked the under board wires with a the multi meter and nothing seems off.  You have any ideas what I've missed?
Thanks!

Title: Re: Rail Voltage on Grids
Post by: EL34 on September 13, 2020, 09:28:33 am

Moved
Posted in wrong board

Title: Re: Rail Voltage on Grids
Post by: sluckey on September 13, 2020, 09:34:02 am

Quote

I've got rail voltage on both power tube grids (94 volts with the variac)

I assume you mean control grids? Pull the output tubes. Still got 94V on grids?

The most likely way to have +94V on the grids of a properly wired PR would be defective coupling caps between PI and PA. But, since this is a new build, I suspect a wiring error.

Title: Re: Rail Voltage on Grids
Post by: Wanabejimi on September 13, 2020, 09:50:46 am

Got it.  Misplaced wire.  Thanks!