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Hoffman Amps Forum image Author Topic: Rail Voltage on Grids  (Read 1737 times)

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Offline Wanabejimi

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Rail Voltage on Grids
« 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!

Offline EL34

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Re: Rail Voltage on Grids
« Reply #1 on: September 13, 2020, 09:28:33 am »
Moved
Posted in wrong board

Offline sluckey

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Re: Rail Voltage on Grids
« Reply #2 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.
A schematic, layout, and hi-rez pics are very useful for troubleshooting your amp. Don't wait to be asked. JUST DO IT!

Offline Wanabejimi

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Re: Rail Voltage on Grids
« Reply #3 on: September 13, 2020, 09:50:46 am »
Got it.  Misplaced wire.  Thanks!

 


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