a single output transformerstereo tube amp ??

I vaguely remember a single ended push pull designation but this seems to be used for OTL amps, like the Philips that used 800 ohm speakers. I do recall seeing a design like this many years ago.

Best I can tell these are 4 ohm speakers I'm actually embarassed because I assumed mono and told teh seller that her stereo was mono based on teh single output transformer

common

be

recall

"Boborann" wrote in news:RcednV1qQN96Od_YnZ2dnUVZ snipped-for-privacy@comcast.com:

I've never heard of a circuit like this, and my experience goes back to the pre-stereo days of "hi-fi". To me, the circuit doesn't pass the smell test. Two stereo channels out of a single output transformer? I have grave doubts.... Sam, what do you say?

That's a hoot but you are right. The difference signal is small in comparison to the main signal so that's how it works. Not a popular design methinks.

Since the output depends on changing flux in the transformer, unless the transformer has some sort of a split core, the output from each of the secondary windings on the transformer will be identical. Let's see the schematic if you have one.

H. R. (Bob) Hofmann

Since the output depends on changing flux in the transformer, unless the transformer has some sort of a split core, the output from each of the secondary windings on the transformer will be identical. Let's see the schematic if you have one.

H. R. (Bob) Hofmann

Quite. I vaguely wondered if 2 mag fields at right angles could be persuaded not to interact too heavily, but that would make a very funny looking and harder to make transformer.

I suspect the amp is in fact stereo with crosstalk... about 100% of crosstalk.

NT

On Sat, 28 Oct 2006 01:43:12 +0000, Homer J Simpson Has Frothed:

Plenty of single ended amps out there but not one have i seen that had one common OT.

design

On Sat, 28 Oct 2006 07:08:52 -0400, Boborann Has Frothed:

Post it to alt.binaires.pictures

Just posted the schematic (90k) and a photo of the amp with transformer (

someone

On Sat, 28 Oct 2006 08:20:32 -0400, Boborann Has Frothed:

It's a push-pull mono amp according to that schematic.

This is like some Grundig amplifiers, where they separately amplify the sum and the difference signals. That other transformer you see in the B+ lead extracts the difference signal and then adds it to one side of the secondary ( L+R ) + (L-R) => 2L, while subtracting it from the other half of the secondary: ( L + R ) - ( L - R ) => 2L. Clever.

I wonder if they licensed thepatent or what? You might try looking up the patents at ww.uspto.gov and see if anything interesting pops up.

This one has two really - a main one for mono and a small one for the difference.

On Sat, 28 Oct 2006 16:26:59 +0000, Homer J Simpson Has Frothed:

Yeh I read that in another post. I looked at the schematic albeit I didn't study it for long.

Nope. Stereo. It looks like one set of speakers is in the cabinet with the 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

snipped-for-privacy@aol.com spake thus:

Nope. No way could it work.

What you say is correct, I'm guessing, for what goes on on the *primary* side of the xfmr. But on the secondary side, as someone else pointed out here, there's no way the split secondary windings are going to be able to selectively pick up only that part of the magnetic flux intended for that channel. In other words, the secondary can only act as one winding (albeit one split in half), so, as someone also pointed out, what you end up with is a stereo amp with crosstalk: 100% crosstalk.

The Way I see it is there is a stereop cartridge where each channel goes through two stages of 12aX7 amplification and the each to its own 6L6 The output transformer is CT with one speaked on one side of the CT in the box The second speaker ( remote ) on the second side of the CT There is even a stereo /Mono switch when when in Mono mode ties both sides of the cartridge together nd adds a cap across teh cathode biasing resistor of teh first amplifier stage I will put a scope on it tomorrow and see how teh outputs are biased as I assume teh6L6's are running class A BOb