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

Hi Syl,

Nice to see you here. ("You can check out any time you like, but you can
never leave." Bwah-ha-ha!!!)

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 ?


No, it's not a major disaster waiting for a place to happen. But it
isn't true push-pull either, in a way "dual-opposed single-ended" would
be more accurate.

This is because two transformers will of course have separate magnetic
circuits. In a push-pull transformer, any change in one half of the
primary will be reflected to the other half. You can get a similar
effect with two SE transformers if you place the primaries in series,
and the secondaries in parallel. Coupling is then via the linked
secondaries rather than via the shared magnetic circuit, and will be
somewhat less than perfect because of "leakage inductance."

OK, so far no disasters. But you won't get one of the biggest advantages
of the push-pull topology, which is cancellation of the DC component in
the transformer. You'll still have the same limitations imposed by
having a DC magnetic field in both transformers.

OK, still no disasters. Now what about impedance? If you place the two
primaries in series, each fed from its own 50L6, the output of each will
still want to see the original output impedance (presumably 4 ohms,
since you're getting these out of old radios). But when you put them in
parallel, the effective impedance is only two ohms! So if you want to
keep the same impedance ratio as originally, you'll have to use two
4-ohm speakers in parallel also.

Alternately, put the secondaries in series and use an 8-ohm speaker!

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


Yes. The turns ratio remains the same, so the impedance relationships
remain the same also. However, be sure that they're indeed identical
transformers! Even a few turns difference can make the combination act
like it has shorted turns! (In other words, if you can avoid it, do!)

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...


Oh, that's ok. You can wonder about such things. But if you conclude
that your MOSFET amp sounds better, we'll all be scrambling to assure
you that you must have done something wrong. :-o

But the PSU is a
multi-taps, SS regulated. It also feeds the filaments
with a current regulated supply. Is this overkill ? ;o)


Yes, definitely. But most of us here like overkill. ;-)

Cheers,
Fred

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 ?


Can I buy some of those off you? I restore said old radios.....

"Fred Nachbaur"

Hi Syl,

Nice to see you here. ("You can check out any time you like, but you can
never leave." Bwah-ha-ha!!!)

Thanks Fred !


No, it's not a major disaster waiting for a place to happen. But it
isn't true push-pull either, in a way "dual-opposed single-ended" would
be more accurate.

Ok, I got that.

OK, so far no disasters. But you won't get one of the biggest advantages
of the push-pull topology, which is cancellation of the DC component in
the transformer. You'll still have the same limitations imposed by
having a DC magnetic field in both transformers.


Oh...so that brings another question then. If DC cancellation is one
of the biggest advantage of PP ckt, what if I use a capacitor in
each branch of the OPT. I would series the OPT then insert
a cap in series of the lower and upper branch of the OPT.
Would that take care of the DC component ? I guess this
should make the OP even a bit more efficient as it will
be less likely to saturate ?


want to
...you'll have to use two 4-ohm speakers in parallel also.

Ok.


...Even a few turns difference can make the combination act
like it has shorted turns! (In other words, if you can avoid it, do!)

Ok.

Oh, that's ok. You can wonder about such things. But if you conclude
that your MOSFET amp sounds better, we'll all be scrambling to assure
you that you must have done something wrong. :-o


-hehe, I'd be waiting for that...

I know Choky fiddled with a Mosfet amp some time ago, never heard
of the results...Maybe he got rid of all his hollow state amps...Nah...
[running and ducking for cover]

Thanks,
Syl

"Syl" wrote in message
news

I know Choky fiddled with a Mosfet amp some time ago, never heard
of the results...Maybe he got rid of all his hollow state amps...Nah...
[running and ducking for cover]

Thanks,
Syl


I can't say more than other Rodents already sayed to ya )
my mosfet fun is not finished yet,hehe0just because I have so little
time,and too fucmuch knowledge,so I'm still in quest to some challenging
schematic;
ya have PA-3B Musical Concepts schematic (mod for Haflers,in
fact0substitute)
huh,I must6 stop now-I start typing almost like our ShivaYoniDim.
Roger


--
Choky
Prodanovic Aleksandar
YU

"Fred Nachbaur"


Well, the rub here is that by putting a capacitor in series with the
OPT, you also kill the DC to the tube -- and nothing happens. However,
you can *also* add a large filter choke to supply DC to the tube

Ooops...I read my post again, I shouldn't post past my bedtime. Yes
I know about the choke. I bought a few good books on the matter and
am reading a lot and learning in the process.

Unfortunately, nothing about series transformers for PP, the reason I'm
asking. Lucky me, Fred is answering...8o)

Now I'm reading on Clough and Loftin White designs, interesting.


So again, you're back to "more iron." Is it worth it?

I would see the whole thing as a learning process. Will see (or Hear)
which is best for a given sets of tubes. I am more at an academic level
as for tubes design and will try to implement my SS design to tubes.
Nuts right ? ;o)

Some people
apparently think so, since it's a fairly popular topology in some
circles. I can't but wonder, however, if it isn't mainly because of the
novelty of the circuit.

I'll let you know...;o)

Syl

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.

"Patrick Turner"

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.

....SNIP...


Interesting reading Patrick...I will put this to good use.

Thanks,
Syl

GOTO alt.binaries.schematics.electronic to see a five page article
by another Australian, Graham J Cohen covering the Dual SE Amp
referred to by Patrick T. Cheers, John Stewart

Syl wrote:

"Patrick Turner"

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.

...SNIP...

Interesting reading Patrick...I will put this to good use.

Thanks,
Syl

"John Stewart" a écrit dans le message news:
...
GOTO alt.binaries.schematics.electronic to see a five page article
by another Australian, Graham J Cohen covering the Dual SE Amp
referred to by Patrick T. Cheers, John Stewart

Hi John,

can't see anything like you say there. I'll wait a bit as I have crappy
service binaries from my ISP but I suspect I won't see it.

Syl