Phil that is a clean design. Nothing extra in the signal path.
I had to look real close to see the bias resistors to the left of the 6V6's. Dual power line input fuses is kind of unique as well. Is that because you are running dual transformers? I'm guessing the 6V6 heaters are in series?
5 Watts in single-ended mode must sound great! Looks like small Hammond iron on the output, with taps for 4, 8 or 16 Ohms. I don't recognize the rectifier...
NOS's tube guy got me a matched quad of 6L6's for my push-pull 11 Watter. Sweet sounding and less than 100 bucks shipped.
I like how you wrote it out on the board, and installed the terminal strips vertically. You win the prize for least number of caps in an amp design! Nicely done and sounds clean.
Jon
good observations!
ok, the dual fuses are there for me when i drop the needle
nose pliers! the power supply is my favorite part of the amp.
instead of tossing in the typical plate transformer that costs
$50 i used a 30 VA 1:1 isolation transformer with the secondary
wired as a doubler with the negative side going to ground.
the filter is a pi with two 330uF caps in series across the
doubler and one 330uF across the output. the inductor
is a 2H 100 mA choke, the supply voltage is 320 volts or
so, the max dc spec on the choke coil to ground is 250 so i
put the choke in the negative side saving some serious
bucks on a choke rated for a higher voltage. the transformer
costs about $10, toss in the filament transformer at $8
and i saved about $30 in just the power supply, an
engineered solution!
the filament transformer is a 12.6 ct part, both 12ax7
filaments are wired across the secondary with filament
centertaps going to the transformer center tap. the
6v6's are wired in series with the common filament
lead going to the transformer center tap.
i've found that modern (cheap :chinese: :001_9898
tubes
have varying filament resistances so a straight series
doesnt work too well even with the 12ax7's.
i plan to make a few changes; add some caps on both
screens, add an riaa phono preamp using another 12ax7
for each channel, change the plate to grid coupling caps
between the 12ax7's and 6v6's from .047 to .22uF to
extend the low end response to about 50Hz, and some
rfi hardware.
:drinkup:
