Tube line-up is 5Z3, 76, 76, 2A3 and 2A3. Can anyone locate a schematic for this one?

Worse comes down to it, it's an amp: not much going on there. Recap and it'll probably just work fine.

Interesting that it is a Webster Chicago (WEBCOR) amp rather than a Webster Electric amp.

It surprises me that two companies in close proximity with each other were making similar products without infringement.

Webster Electric was in Racine Wisconsin.

-Steve

Thanks for the suggestion. It has been recapped and has low volume and some distortion. It has a weird winding that seems to parallel the plate windings on the output transformer. The plate of one of the 2A3's is running at 400V, the other at 195V. Can't trace easily because the wires are string wrapped. (I'd hate to unwrap all those wire bundles.) Double checked all caps and resistors. Sub'd in two sets of 2A3's. Likely a bad output transformer, but it would be nice to have a diagram to check against. Cheers, Russie

Russie,

I just finished working on one of those, looked everywhere for the schematic but no luck. I traced the circuit out, extremely odd design of the preamp stage. This one uses 56's instead of 76's. The grid choke going to ground on the second 56 was open and I have no idea what value it was. I could not get the amp to actually work well with chokes I had on hand so I rewired it to be like a Webster 6013 amp and it works great now.

For a Selectaphone, right?

The pickup is a real PIA to rebuild.

I can send you my sketch of the original and the modification I did.

Chuck, that could be very helpful. Please send it along with my thank you in advance. Best I can tell, it has a parallel output configuration something like this. What do you think about replacing TA with a pair of resistors? Cheers, Russie

If your amp uses that CT choke in the output stage it isn't the same as the SB6 I have. Take a look at a model 6030.

I have no idea what the specs are for that choke. If I was working on it and couldn't find an original choke I would use a universal output transformer or locate an old stock unit for 2A3 outputs and change the output circuit to a standard push-pull stage.
Another option is to measure the DC resistance and inductance of the good half, measure the wire size and check with Heyboer Transformer to see if they can make a replacement from that much info.

Are the tube sockets marked for 76's? or did somebody decide to upgrade from 27's

Chuck

Thanks for that. After some closer inspection, I found that TA appears to be a replacement, or a modification (the mounting holes have been elongated). I think I will follow your advice and replace both with a universal output. I see a few on Ebay, but I think my surplus sources may offer a better deal.
The tube sockets are marked 56 (not 76, I need to wear glasses!), however, in one of my years ago experiments (in another amplifier), I sub'd a 27 for a 56 and found it worked fine. (One of the electrical differences between the two VT's is that the 27 draws an additional 1/4 Amp filament current, so I wouldn't want to sub in several.)
This amp is from a Selectaphone, but will be a temporary amp for my Electramuse, mated to a Jensen Type D 5 speaker (while I look for the correct amp).
Again, TY for the advice. Cheers, Russie


PS, pulled out another Seeburg amp to compare and it appears to be nearly identical, though it is an SB-7.

Good news! I found a compatible output transformer and put it in place of the two parallel transformers TA and TB (above). Wow, this little amp has great power. I fear it will overdrive the speaker if I don't lower the gain on the input stage. Thanks for the advice guys! Cheers, Russie

Bad output transformers are not uncommon; I have seen that many times.

Maybe a bit too common for these early amplifiers, since it is nearly impossible to find the exact replacement. Somewhere I saw someone had posted a list of transformer rebuilders (rewinders?). Can't seem to locate it now.
Cheers, Russie

Have you Webster-Chicago folk looked at all the Webster-Chicago/Rauland schematics available in the Rider's PA book?
I can take a look if anything close is there and send scans if you can post model numbers/and/or tube line ups for each type model?

A lot of these amps ya'll are workin' on, are from the mid- late 1930's before Webster -Chicago sound systems was bought out by Rauland in 1940.
Webcor was a separate division not sold with the Webster-Chitown sound amplifier division to Rauland
Webster-Electric of Racine, WI. (later Sta-Rite Corp.) seems confusing with "Web-Cor" as post war into the seventies both companies made similar quality audio visual equipment for institutional use such as RTR's, filmstrips,et al.
Kent

Kent.

Nothing in the PA book. The amps in question are from the late 20's. There are some similar schematics in
Riders Volume 3.

Thanks Chuck,
I wondered why they weren't in there (though some similar 6C6 circuits under "Rauland" that were originally W-C circuits were there) in the
Boat anchor PA book
I must have seen them in the Vol. III manual then, looking for some old radio....
Kent