I have a weird pair of amplifiers (?) visiting my house. I thought I knew what I was getting myself into... but I don't!


https://live.staticflickr.com/65535/48829368853_cfe6b077fe_b.jpg (https://flic.kr/p/2hoThaT)DSC_6928 (2) (https://flic.kr/p/2hoThaT) by Mark Hardy (https://www.flickr.com/photos/42750692@N07/), on Flickr

I was thinking PP 6L6, and someone had (apparently) added an RCA jack input and a pair of 5-way binding posts for output. They come to life just fine, but pass extremely little signal.

Then there's the tube complement. 2 5U4, 2 6L6 and one 6J5(?!).

I am not finding much.
One tantalizing thread and one old auction listing make it fairly evident that these used field coil drivers, which might explain the issue(?).

https://www.antiqueradios.com/forums/viewtopic.php?f=13&t=220408

So, one 5U4 for HV and one for a FC supply, maybe?

And then there's that 6J5. One triode, and two 6L6s? I mean... that won't fly for a PP amplifier, and it's hard for me to conceive that this is a single-ended, parallel 6L6 amp!?!

It's not just a regulated P/S, is it?!?

Any of youse guyses know anything about this (these)?

Anybody got a schematic? :)

Man, I feel so dumb...

:tongue:

https://live.staticflickr.com/65535/48829754816_f69a33dfec_b.jpg (https://flic.kr/p/2hoVfUq)DSC_6920 (2) (https://flic.kr/p/2hoVfUq) by Mark Hardy (https://www.flickr.com/photos/42750692@N07/), on Flickr

Well, I am not an expert on this at all, but according to the interwebs, if it is intended for a field coil speaker, it's very possible the field coil is also part of the power supply, so has to be connected before the amp will fire up. Have you checked if there is reasonable plate voltage on the 6L6's and 6J5?

Could they be the amplifier chassis, removed from a big radio or organ or something? Perhaps most of the gain was originally on another chassis, connected via those multi pin plugs near the back.

https://antiqueradios.com/forums/viewtopic.php?f=11&t=306433

You can sub a choke for a field coil, and you can build a preamp chassis with the needed audio gain to drive them.

If they were mine and I had to make a new chassis anyway I'd take the power and output transformers and tubes and find a nice HIFI amp circuit that the parts lend themselves to and build an integrated single chassis stereo amp...
It is kinda sad to think 2 fairly high end consoles probably got chopped up by audiophools to put those amps in your hands like that.