Re: Homebrew 6V6 amp, sounds bad at clipping, what to do?

"f.leghorn" <fleghorn@xxxxxxxxxxxxxxxx> wrote in
news:1157817209.576120.261310@xxxxxxxxxxxxxxxxxxxxxxxxxxxx:


I am just finishing up an amp with a similar PI, and 4 - 6V6, cathode
biased output. Perhaps the following may be helpful. Below numbers are
in heavy AB (single 78 ohm 6V6 Rk), idle 54 mA each. This runs class A
up to about 22W, like an old AC30. No feedback.

PI is a 6SL7GT, 68/82K plate resistors, 470 ohm bias resistor, 10K
tail. 5K presence on the bottom. 0.01/0.1 coupling caps, 470K grid
resistors. So, aside from those 470ks, it's pretty much a standard
Marshall PI adapted to a 6SL7. I get the following numbers (bear in
mind my shop "120" VAC usually runs about 124 V). All measured with
Fluke 187.

DC --- B+ 310, Vp 208/198, Vk 43.6, grids 33/34, top of tail 42.3,
bottom 14.2. About 1.5 mA/1.3mA plate currents respectively.

AC --- 400 Hz sinewave, 0.100 V input, vol & MV dimed, PI input 7.96
V, Vp out 53.63/52.13 V (<3% out of balance).

This gives 234 mA at 225V avg. on 6V6 plates, so about 37 W, and real
loud 'n proud.

Even at this level it sounds good to me, although a bit hard to
control with the feedback out. W.FB in, 100k off the 16 ohm tap, it
becomes more controllable but less "tubey". I normally run it backed
off slightly from these settings. Running a Strat w/ Fralin vintage +
set.


Thanks for that, I'll do some final checks just make sure mine is running
happily. Sounds similar to mine but I am not using NFB now.
.

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