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Hoffman Amps Forum image Author Topic: Where to ground power-amp grid-leak resistors  (Read 2690 times)

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Offline PharmRock

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Where to ground power-amp grid-leak resistors
« on: April 11, 2022, 03:03:03 pm »
Should the grid leak resistors on the power tubes (in this case a cathode-biased 2x EL84) be grounded with the power amp cathodes, or with the PI tail resistor?  I'm thinking it would make sense to go with the power tube cathodes.  I've read this http://www.valvewizard.co.uk/Grounding.html and it seems that is the case based on some of the figures I checked out.

There is no NFB in this amp, and the PI plates are tied to a can cap that shares the ground with the pre-amp tubes filter cap.

Thanks

Offline Latole

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Re: Where to ground power-amp grid-leak resistors
« Reply #1 on: April 11, 2022, 03:19:17 pm »
This Fender amp layout and schematic may help you




Offline Latole

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Re: Where to ground power-amp grid-leak resistors
« Reply #2 on: April 11, 2022, 03:19:46 pm »
Schematic


Offline sluckey

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Re: Where to ground power-amp grid-leak resistors
« Reply #3 on: April 11, 2022, 04:11:58 pm »
Quote
I'm thinking it would make sense to go with the power tube cathodes.
Yes
A schematic, layout, and hi-rez pics are very useful for troubleshooting your amp. Don't wait to be asked. JUST DO IT!

Offline tubeswell

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Re: Where to ground power-amp grid-leak resistors
« Reply #4 on: April 11, 2022, 04:59:02 pm »
Yet another schematic/layout. (Adapt to suit for different pre-amp type-ologies)
A bus stops at a bus station. A train stops at a train station. On my desk, I have a work station.

Offline PharmRock

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Re: Where to ground power-amp grid-leak resistors
« Reply #5 on: April 11, 2022, 05:42:12 pm »
Thanks everyone.  I've changed the schem/layout so that the EL84 grid leak resistors connect to the ground for the shared cathode resistor on the EL84's. 

Offline PRR

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Re: Where to ground power-amp grid-leak resistors
« Reply #6 on: April 11, 2022, 07:19:27 pm »
It should not matter.

Maybe less to go wrong if nailed to the cathode return. (Since we keep hearing of amplifiers with two ground busses/points not firmly connected.)

Offline PharmRock

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Re: Where to ground power-amp grid-leak resistors
« Reply #7 on: April 11, 2022, 07:28:07 pm »

Maybe less to go wrong

Good enough reason as any as far as I'm concerned. 

 


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