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Uses four 807s, has a couple toroids, 4 mic inputs, 1 phono, pretty cool. Its at least 30 inches long. Model is MI-12???. The sticker is partially missing. Anyone seen this one before?
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Looks like a lot of cleaning before you can even think of powering it up (with a Variac if possible!) You may want to (should) replace all electrolytic capacitors...
4 807s can be capable of well over 100W, but the transformers in this case look a bit small for that much power. More likely RCA designed this so the tubes wouldn't be stressed.
Good luck restoring!
Its an MI-12293. 33" long!
Was made around 1950. I could send you a copy of the schematic if you need one.
I am assuming the toroid near the ac input (in the middle of the amp)is power and the toroid next to it is filament? Then the big square one is output and the smaller one is a choke? Thanks, Bobby
The large square xfmr is the HV plate supply, 840v CT, .290A.
The small square xfmr is the filament xfmr, it has a 5V winding for the rectifier tubes and a 6V winding for all the other tubes.
The round can next to those is a choke, 5.5H, 81 Ohms DCR.
The round can next to the 807's is the output xfmr, 3.7K pri to 4, 8, 60 and 250Ohms.
BTW, I doubt that the two round units are torroids. Those were not in common use in the 50's. They are probably standard laminate cores potted in round cans.
Hope that helps. Al
"BTW, I doubt that the two round units are torroids. Those were not in common use in the 50's. They are probably standard laminate cores potted in round cans."
That's correct. Those transformers in the cylindrical cans are UTC Commercial Grade intended to be used in PA amplifiers and similar equipment. They may have the UTC number on the cans, but they also could be custom built to specs. provided by RCA.
There were a series of these amps in different power points. They show up on epay frequently. You might be able to find a mate for this one.
NT
Hi bcguitar.
I have one of those, it is mounted in Brazil and the model number is MI-12205.
Here is a useful link:
http://www.theused.com/manuals/rca/rca_mi-12291_12293.pdf
Regards.
Walter.
Only tubes play music!
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