Re: a single output transformerstereo tube amp ??

I have never seen such a design, I didn't see a link to the pic, so I
am flying by the seat of my pants here.

First of all such a thing might be stereo, or hi fidelity, but not
both. To explain, my definition of stereo is that there are two
seperate, discreet and identical channels. Perhaps is is very high
fidelity when used as a mono amp, but actually was capable of stereo.

Using a large main output transformer for the mono signal, typical push
pull, but the if the primaries are split up and phased just right I can
see how this can be accomplished. Of course then you have the
secondaries of the small transformer in series with the secondaries of
the big transformer. The way I see it, the arraingment of the primaries
is important, otherwise you get alot of second harmonic distortion, IMO
an unacceptable level.

The only way this can work is to feed L+R to the 6L6s in differential
mode, and the L-R in common mode. By splitting the primaries so that
the differential mode current is bucked effectively in the primaries of
the secondary output transformer, and the common mode current is
doubled, acceptable performance could be achieved IMO.

The whole thing sounds quite inefficent to me. If the seconday output
transformer is not equal in output to the primary, the amp cannot
deliver it's rated power into one channel only, even though that is
rarely needed.

I can see it is simply a matrix. This is pretty much the same way FM
stereo, or NTSC/PAL colorplexing/decoding works. The difference is that
the levels are higher.

On the drive side of such a circuit I bet the negative feedback network
is a beauty to behold. (lol). Actually if I were to design such a
circuit, each 6L6 would have it's own completely independent feedback
system. Even then I would expect quite a bit of second harmonic
distortion in the difference channel, i.e., anything that comes out of
only one side, and to a lesser degree when panned partway to one side.

Music mixed in modern times often has some phasing effect, sometimes
they "pan" using a time delay. When used judiciously it doesn't sound
like an effect, but it allows them to spatialize the sound left or
right without a great change in the levels coming out of each side. So,
I wonder how one of these things would handle modern music.

It probably sounded good on orchestra music, basically anything that is
miked, but I have heard some music that would probably sound terrible
on it. Some of the old Beatles comes to mind.

At any rate, I think this an interesting topic, thanks for bringing it
up. Today, this is thinking outside the box. :-)

JURB

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