• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Can you identify these tube amplifiers? 4x807 & mercury vapor rectifiers

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Can anyone identify these amplifiers? They got away from me on ebay years ago, and I've always wanted to know what they are. I would love to have a schematic.
 

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They look like renovated amps from the early to mid 1950s, given the octal valve bases, the use of oil-paper caps, and two chokes (large & small). The other small choke and can caps may be related to a bias supply.

There was a lot of US-based Williamson amp modifications going on in that period - certainly the use of quad 807's and the need for increased diode capability than just available form a single valve, so as to increase the power rating of original Williamson from 15W.
 
They certainly could be a custom design. However, based on the little the seller shared, I am hoping they were a commercial design and someone will have a schematic.

I did look back at my correspondence, and the seller believed these came out of a movie theater, were manufactured under the Operadio brand, and were model 1A50.

I have never been able to find any information that linked Operadio to any large amplifiers like these, however, and I have never found information on a model 1A50.
 
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