Quote:
Originally Posted by
chconnor
β‘οΈ
Brilliant - thanks!
Last question, I swear: from
the schematic you mentioned C2, C10, and C15. Should I include C30 in that list?
Ahh, that sure looks like an afterthought "add-on". Looks like someone wanted a pre-output-stage, output tap/insert point. It's a coupling cap that's only used if you use J5 to feed something. Otherwise it won't affect the amp's sound.
Certainly change it as long as you're in the amp. Since it's a 25uF electrolytic, it really should have a DC charging path instead of just being connected to the output jack (with no DC return). However you don't want to load that point too much because its part of the feedback loop around the output stage and output transformer.
I'd add a small resistor (20 k ohms) from the low side ((-) lead) of C30 to ground (in parallel to J5). I'd also avoid loading that output (if you ever have a use for it) with anything less than a 10k or so input load to avoid reducing the output stage negative feedback. Too low an impedance there will eliminate the negative feedback and might make to output stage unstable.
You might want to add a 1 or 2k ohm resistor in series with J5, just to prevent the possibility.
Adding an output there is definitely a "kludge"

Also, there is no AC coupling to the "insert" (ring) of J5. It goes directly to the grid of the 6BQ5, so anything connected there should be AC-coupled only. Connecting something with a low impedance, DC-coupled output will kill, or at least change, the grid bias on the output stage.