Syl wrote:

Here's a dumb one.

I am more familiar with SS than tube audio so forgive me if this
question sounds "simple".

I have access to a ton of SE OPT used primarily for old radioz
using 50L6 and similar OP tubes. I was thinking of using two of
those txfmrs in series to build a PP OPT using a pair of 50L6
as an experiment. Has anyone done this or is Major Disaster
waiting for me ?

Also I've seen schematics with OP txfmrs in parallel to
support a higher total output, is this acceptable ?

A while ago I asked info for building an 807 PP amp,
it's in the works and will post when done. Can't wait
to listen to it thru my Tannoy Dual Concentric...Wonder
if it'll sound better than my Mosfets amp...Mmmm...
I shouldn't say things like that here...But the PSU is a
multi-taps, SS regulated. It also feeds the filaments
with a current regulated supply. Is this overkill ? ;o)

Thanks,
Syl

Your idea of using two SE transformers for two tubes in PP
will work quite well, but you'll have to limit the operation to class A,

not class AB.

So basically, build two SE output stages, with a driver stage,
just the same as you normally would,
complete with their own loop of NFB.

Then use a phase splitter ahead of each amp, so each
amp is supplied with an oppositely phased signal at its input,
so you can get a balanced output.
If you have provision for 4 ohms matching for each amp,
then an 8 ohm load can be connected across from one amp to the other.
So what you end up with is a Bridged Pair of SE Amps,
and the power output is twice what you'd get from one amp.

The mainly 2H distortion of each amp will be similarly phased.
Thus the distortion voltage from each amp is the same, and appears
at both ends of the load, so no distortion current flows in the load.

Expect extremely low thd in such an arrangement, for the first few
watts.
But as the power gets higher, the exact 2H cancelling
is impossible, and you get 3H produced since each half cycle
tends to flatten.

I knew a guy who built a hi-fi amp in about 1960
and that used SE radio trannies, with 2 x 6V6, and it was a pure class
A,
and when in class A, one can simply have two SE output tubes,
a normal PP driver stage, and parallel the secondaries,
making sure the phase of the secondaries will be the same.
There will then be the usual 2H cancelation,
since the two primary halves of the circuit are mutually coupled via the
secondaries
of each tranny, and although this coupling is looser, ie, there is a lot
of leakage inductance
between one tranny primary and the other, this isn't critical as long as
the
amps are in class A. Only one loop of NFB is required.

Its a poor man's way to PP, but better than no way.

My friend's PP SE set sounded great in 1960.
But we were mainly into Beebopalulah, Peggy Sue,
and all that stuff.
It had much better sound than our parent's SE radiograms with SEP 6V6,
with hardly any NFB.

Patrick Turner.