Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: MORE_Guitar_Solos on May 05, 2026, 06:41:10 pm
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Hello all,
I've been searching for a straight answer to this for a while, but came up confused. Trying to sort a nice ground scheme for my half-power AC30, and while I understand the PT center tap, power tube cathodes, heater reference, and reservoir cap can all share a common "dirty" ground point near the PT, and all of the rest upstream (starting at PI?) should be connected near the input jack, which way should the "B" screen supply node go? Is it ok to share the dirty ground or should this go to the input side? Should it have a separate ground point? What's best for quiet operation?
Thanks in advance and sorry if this has been covered elsewhere, I just couldn't find a clear answer.
Cheers,
Dave
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My crystal ball is pretty clear. It says ground the screen node cap at the same place the plate node cap is grounded.
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Perfect, thank you Sluckey! That's the (perhaps obvious but somehow elusive) missing bit I needed.
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... half-power AC30 ...
The AC30 was originally a kinda doubled up AC15 :icon_biggrin:
From personal experience, if you read Merlin's document on grounding enough times, it might eventually 'click'.
https://www.valvewizard.co.uk/Grounding.pdf
To minimise heater buzz leaking into the signal path, the 6.3V heater circuit could be balanced and referenced to the EL84 cathodes (DC elevation).
Yes, even just that 10V is beneficial.
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Thanks pdf64, elevating the heaters is definitely in my plan (have I already done it?)