Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: dennyg on December 16, 2016, 07:47:31 am
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I've just about completed a rebuild of my first amp, a 2-channel version of the AX84 SEL design, completed a couple years ago. The last bit of tidying up is OT placement. When I first built the amp, I'd mounted the OT right next to the PT per layout, but upon learning of the headphone trick, had moved it to the lowest hum position - directly over the preamp. After a few weeks of researching squeal and oscillation causes, learned about how OT's work and then moved the OT to middle of the chassis where it's remained since. The rebuild has been very rewarding, yielding a very quiet, amazing marshally tone machine, thunderous at full throttle. At idle, there is no hum until MV is past 90%, but then only slight and not a concern.
But the secondary leads run beneath the tone stack filters on the board (see gut shot below), which just bothers me out of principle. One thought would be to run those leads on top of the chassis and drop them in right next to the speaker jacks (which are also near the preamp but fortunately did not repeat that error on later builds!). Also for my later builds, the OT was happy right next to the PT, so not sure why this isn't the case with this pair.
Would you guys leave it as is, or is there a benefit (or caution) for running the secondary leads across top of chassis? Or other suggestions regarding placement compromise when the OT is happier further from the PT vs right next to it?
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I would not obsess about secondary leads as they are not a lot higher voltage than many internal signals.
I have run Primary leads outside the box to keep the much higher audio voltages away from small stages. That does demand much care for user safety.