Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Jalmeida on June 17, 2023, 11:41:49 pm
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Hey all,
***Updated*****
I have been tinkering with my next build in between things and I have been lucky enough to have been gifted a Vox AC30/4 repro chassis setup from a super cool amp guy. So my next build will be an AC30/4 fawn head.
Anyways, I have been learning how to use DIYLC and as a learning opportunity i put together a layout diagram for the AC30/4. Thought i’d share for anyone interested. I’d recommend it get proofed against the schematics.
***FYI this layout is based off the original layout. ****
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Original layout files replaced with updated. Attached schematic.
Updated Schematic correcting a few resistor labels.
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Congrats on the amp! Not a fan of using the chassis as a ground plane but otherwise it looks great. In case you're wondering what this means? Run the preamp and output tube grounds directly to their respective power filter caps' grounds eliminating the ground lugs to chassis, then run them all to the power transformer bolt lug location since there's not a HT center tap for the resevoir cap. Also, there's no center tap for the heater wiring. I'd run a couple 100r's to ground forming a virtual center tap here as well.
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Congrats on the amp! Not a fan of using the chassis as a ground plane but otherwise it looks great. In case you're wondering what this means? Run the preamp and output tube grounds directly to their respective power filter caps' grounds eliminating the ground lugs to chassis, then run them all to the power transformer bolt lug location since there's not a HT center tap for the resevoir cap. Also, there's no center tap for the heater wiring. I'd run a couple 100r's to ground forming a virtual center tap here as well.
Thanks for that. I made this to represent the original AC30/4 layout. They could have made many improvements to this layout with regards to ground practices. But this will get you original layout if one is doing an authentic build.
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Updated to add schematic.
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Rev 4 Layout corrects input jacks.
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Rev 4 Layout corrects input jacks.
The HI/LO jacks are mislabeled. The jacks with the 1M are the HIGH jacks.
Also, the alternate speed pot is miswired. The blue wire should be on the right-hand lug.
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Rev 4 Layout corrects input jacks.
The HI/LO jacks are mislabeled. The jacks with the 1M are the HIGH jacks.
Also, the alternate speed pot is miswired. The blue wire should be on the right-hand lug.
I sure did! Thanks for that. Corrected on the layout an uploaded. I wouldn't have caught that until power on likely. Possibly not at all on the High/Low Jacks.
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Rev 5 uploaded with Sluckey corrections.
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Corrected layout page 1 to R6 and corrected schematics as well.
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Many thanks for this - looks really good and super useful. I think I will download and have a go with this software as I’ve seen a number of excellent layouts that must have been done with it.
Only one thing I can spot - unless I’ve missed it, there doesn’t seem to be a heater ground shown on the layout. As far as I know, there was no CT on the heater windings and JMI tended to ground the heaters on one side only, in the pre-amp, often next to the Phase Inverter valve. All of which is a terrible idea, of course - they are much improved if you install a virtual centre tap on the heaters and ground it to the cathode of the EL84s to lift the reference voltage but that’s another story!