• The move to the new server is done. There are some software and database maintenance updates in process. This has us passing the hat around to help out. We appreciate any donations. Seriously, even a dollar helps. The payment page may be found here - https://www.audiokarma.org/support.html

Three-output-transformer amplifiers....

Old1625

Old1625

Super Member
Has anyone here ever had dealings with bottom-end stereo phonographs--either portable or small console--that employ 3 output transformers? There are two smaller ones for "wing" or "satellite" speakers and one larger one that drives a center speaker of somewhat larger size.

The "wing" transformers--instead of having their red leads go directly to B+ instead draw through the blue and brown leads of the center "push pull" transformer, essentially making the output tubes serve as left and right "wing" channels for stereo, and delivering a "mono" push-pull signal to the center speaker.

I've personally never shaken hands with such a unit, as I had always gone for the big guns sporting 6L6s and 6550s back in the day. But the way I see it wired in schematics it would appear that one wing speaker would be out of phase with the other, (if the push-pull action is going to work correctly) inducing an annoying "wide" image. My instinct would be to reverse the leads on one wing speaker to correct this--which one depending on the phase relationship with the center speaker.

Has anyone encountered one of these gems?
 
Last edited:
Register to hide this ad
Yes, phase of the wing speakers will be opposite. Don't know if I have one of these schematics around, but I'm sure it would show speaker phase dots...
 
True it should be, but the Sams schematics all show the phasing dots in the same polarity. The phase inversion if the center channel is to work at all would have to be a product of the hook-up at the pickup cartridge.

Of course anyone that has frequented Sams folders knows that they are capable of errors....
 
Motorola and Guild used this setup but not in the config you mention. The 3rd transformer took a bass bleed from the other 2 and was powered more heavily for a "seperate" bass channel.

Im fond of the Moto units and have a couple right now.
 
I can see--and have seen--arrangements with SE satellite channels and a PP center channel, but there was a separate pair of output tubes driving the center channel transformer. The one I posted about uses but one pair of output tubes pulling double duty. I can only imagine the intermodulation distortion, as I don't remember actually seeing such a configuration.
 
GordonW said:
Wow. That's pretty g**d*** clever... even getting phase inversion by wiring one channel of the phono cartridge backwards. It's phase-inverted on one channel, throughout the amp!

But I do have to also wonder... what did it SOUND like?! Could have been a real train-wreck?!

Regards,
Gordon.
Click to expand...

Actually it's not bad. I use it in my workshop on a regular basis
 
Old1625 said:
My instinct would be to reverse the leads on one wing speaker to correct this--which one depending on the phase relationship with the center speaker.

Has anyone encountered one of these gems?
Click to expand...

One of my tube techie buddy's did just that with the (standard) motorola chassis - he's a real EE, so I trust him :thmbsp:

he removed all the guts from the chassis, and did a funky plexiglass cube . .. I gotta grab some pictures next time I see him :yes:
 
GordonW said:
Wow. That's pretty g**d*** clever... even getting phase inversion by wiring one channel of the phono cartridge backwards. It's phase-inverted on one channel, throughout the amp!

But I do have to also wonder... what did it SOUND like?! Could have been a real train-wreck?!

Regards,
Gordon.
Click to expand...

'At's what I thunk!
 
markus said:
One of my tube techie buddy's did just that with the (standard) motorola chassis - he's a real EE, so I trust him :thmbsp:

he removed all the guts from the chassis, and did a funky plexiglass cube . .. I gotta grab some pictures next time I see him :yes:
Click to expand...

I look fwd.
 

Attachments

  • Arvin_SE-7591_Inside1.jpg
    Arvin_SE-7591_Inside1.jpg
    193 KB · Views: 61
  • Arvin_SE_7591_1.jpg
    Arvin_SE_7591_1.jpg
    185.2 KB · Views: 50
  • Arvin_SE_7591_SideRear_1.jpg
    Arvin_SE_7591_SideRear_1.jpg
    45.8 KB · Views: 39
Since this thread is less than a week old I'll resurrect it. I just came across a portable (ok luggable) Zenith stereo record player LPS-80. Its got a 6X4 rectifier 12AX7a driver and two 6AQ5 output tubes. It's got 3 OTs, two smaller ones running 2-way satelite speakers are single ended for sure... then there's a larger OT running to where there used to be a center or bass speaker. There are 3 wires on the primary side. Appears to have a center tap that is tied into the 3rd power cap, which then hops to pin 8 of the 6X4. filament? I'm still a bit baffled as to what the design is supposed to do. I haven't traced the circuit but does that make any sense?

I'll look again tomorrow when my eyes are in better shape and maybe trace out the circuit. There's not much to it. I think my preference would be do disconnect the center or bass channel if that's what it is and run standard 2 channel.
 
Last edited:
As I dropped off the detritus from my annual yard sale at the Salvation Army, I spied a Zenith LPS-80 sticking out of a giant box of mostly BPS speakers. A few Washingtons later and it's in my truck. Looks complete and fairly clean,
 
You must log in or register to reply here.
Back
Top Bottom