[sdiy] Tube amp solution!

[Justin Herrmann]

Well, to give some closure to this issue, Rene hit the nail on the head
with his response.  Our (final project group) output tubes were having
problems because we had left the secondary of the output transformer open,
and we were getting "inductive kickback" from the primary.  We attached
an 8 ohm power resistor to the secondary, put in new tubes, and everything
was fine.

I had to go through some trial and error to determine the right component
values that would get us to the right bias point, so now Rs=6.8k, Rk=120,
we're only using half of the primary (to reduce the DC flux in the core of
the transformer), and I connected the 8 ohm speaker to the 4 ohm tap on the
secondary.  I also replaced the series grid resistor with a short, and
reduced the shunt resistor to 270k instead of 1M.

Now the amp works just as it should, and it sounds exquisitely tubey.

Thanks for all your infinitely helpful suggestions.

							-Justin Herrmann-