Steve,

The aforementioned amp I built used the Hammond 125E OT. It can
be used for SE operation or push pull and is good for about 10-15
watts SE or up to 20 watts for push pull. Best of all it is around $30
US. There are a few others that will work for an SE 6L6 or EL34,
but these tend be around $100 US.

I built a tweed Princeton clone with an OT from a Bogen PA amp
that was supposed to use a SE 6L6 (bought it surplus from All
Electronics many years ago). It is built as a combo in a pine cab with
one Alnico 12" I salvaged from my dad's old stereo. I set up the amp
with an adjustable cathode resistor so that various output tubes can
be used. The plate voltage is around 300V so that 6V6's can be
used. I also installed a pot for variable feedback in the power stage.
Talk about fun! The simple circuit really allows the power tube tone
to shine. I have tried 5881's, 6L6 of all types, and different EL34's in
the amp. All sound very different.

By far my favorite is a Mullard EL34, BTW. It really has that
"marshally" midrange response. This effect decreases with increased
power stage feedback, however.

This amp is one of my favorites as it is fun to play, fun to work on,
and I can crank the fool out of it and my wife and babies don't mind.
The amp has a low B+ so the power output is under 10W even with
an EL34 or 6L6. It records well also. I really recommend such an
amp and would build another if this one died.