more audio results

OK, yep.  I hooked it up to the real 12" speaker, and through the AB763 preamp, with the boost stage engaged, it gets *pretty* loud.  Almost loud enough, I suppose -- certainly louder than I'd want it, most of the time; however, I don't think it's actually driving the 6L6s to anything like the full 100W.  Maybe it's 25W or so.  I'd have doubts about being able to keep up with a loud drummer.  In fairness, given the single 35W Celestion, I'm not eager to push 100W anyway.  But I want the circuit to be capable of it!

With the boost off, it's simply not very loud through the AB763.  And through the VTX, it's never remotely loud enough.  Must be a good 12dB below a reasonable loudness.

So I could "fix" the VTX situation with some opamp work I guess, but all in all, the power amp driver is just not sensitive enough.  Claiming the third 12AX7 section for boost in the AB763 was just wrong, it is needed to gain-up before the lossy cathodyne stage.

So one possibility would be to put the third triode section back with the power amp: in other words, send both preamps into this stage instead of coming after; then there'd be no boost, too bad, but at least things might work more normally.  And then I could do the nfb into the cathode of the third stage, and probably get that to work better too.

However, another tempting possibility would be to add a third 12AX7.  Then the existing third stage could be the power amp pre-gain stage, and the new 12AX7 could be a two-section boost circuit: e.g., I could do a full "M-style" gain circuit.  I just don't know if the power transformer can handle the extra heater current.  I guess the way to find out would be to wire in the third 12AX7 temporarily, and just run it for a while and monitor the temperature of the power transformer.  Given my apparent inability to get any info about this transformer out of Peavey, that is.

Oh, another problem I found is, I have the bass control wired backwards, ccw is max-bass.  Oops.  I think I've done this before!

(BTW: I'd just like to point out, the 6L6 tubes in this unit are a quad of Peavey-branded tubes.  I.e., very likely the original tubes it shipped with from the factory, in 1980 or whenever.  Still going strong!  And the blown speaker in this amp was testament that it has been played hard.  The notion that tube amps are "less reliable than solid state" is a total myth.)


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