Mystery RCA amplifier

[Mixwell]

Found this in the shop many moons ago. It has no model ##, just says "Amplifier"....

We are curious if Any RCA experts out there know what it is.

I already sent an email to Doug Fearn, since I figured he had some useful knowledge to share.

This thing has the biggest UTC trafo' I have ever seen.

[Mixwell]

This thing is definitely a 180 watt power amp. I have to get this working. I am going to guess and only assume that the metal holes on each side are for looming a speaker wire through, as the terminals are at the bottom near the control panel. WOO, HOO!!!!

[Mixwell]

DWF wrote this;

Adam --

This may have been part of the movie theater sound system. RCA had their own film sound system in the 1930s (in competition with the Western Electric system), and I believe they supplied all the equipment from the microphones on the set to the speakers behind the screen. The amp you have would seem to be the right vintage (probably 1940s or late 30s), power, and construction.

If you want to get this monster going, be careful. The filter capacitors are probably shot, and if they are electrolytic, they could easily explode when you apply power. They may be oil-filled capacitors if the unit is old enough.

I would start by replacing any electrolytic capacitors. Then put a load on the output (like an 8-ohm, 100W resistor), and short the input. Bring up the line voltage very slowly with a Variac, starting at a few volts and increasing it gradually over a period of hours by a few volts every 15 minutes or so. Keep an eye on everything for signs of overheating and stop if anything starts looking bad.

You will need a Variac that can handle the current -- probably 10 amps or more. If you can't find a Variac, you can make up a test rig using about 10 light bulbs (real incandescent bulbs, not compact florescent) wired with the bulbs all in parallel and the entire string in series with one side of the AC power to the amp. Start with all the bulbs out, and then screw in one low wattage bulb (25 watts). Monitor the AC voltage to the amp. It should be low -- about 10V or so. Let the amp run like that for a while, and, like with the Variac method, bring up the voltage slowly over a period of hours by screwing in more bulbs. By using different wattages, you can adjust the voltage to the amp. Higher wattage bulbs will bring the voltage up more than lower wattage bulbs.

There appears to be a couple of more modern resistors in the photo, so perhaps someone has worked on this recently. What they have done might be good or bad.

You need to find a schematic and any other info on this thing at some point if you really want to get it going and keep it working. Some time spend searching for info will be well worth it.

Then you will have to find a matching unit to drive your stereo speakers!

Good luck!

Doug

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Confirms the Shadows thoughts, when I asked about "what it looks like"...

He said, "dangerous"

[Mixwell]

This just in - The good Fellow Mike Cleaver of PSW Found what he thinks [99% sure] would be our Schematic. Link to thread below. Possibly Model RCA MI-9377A.

http://recforums.prosoundweb.com/index.php/m/483763/17028/#msg_483763

[moose]

Interesting... I sorta doubt its 180 watts, a quad of 6L6 tubes is about 80-100... maybe a buck 120 at full capacity, like a Fender twin. Why are their two rectifier tubes? The 65L7 is an oddball too... usually see those in early '50s Fenders as preamp tubes. Pretty sure the meter is a "tube check" type... other then that, not a clue!

[Mixwell]

Interesting... I sorta doubt its 180 watts

Moose, it says 180 watts, but I also have no clue. Hopefully the She-matic Mike helped me find will lead to getting this behemoth operational.

[Tim Farrant]

It might do 180 into 4 ohms?

[jeffreyjamesmusic]

gimme!