Jeff Duntemann's Contrapositive Diary Rotating Header Image

February 6th, 2012:

The Comco Whatchamacallit


I hung yet more Elfa shelves downstairs the other day, on the only remaining blank wall in my peculiar workshop. I’m trying to get stuff off the floor and into some semblance of order. A number of tube-era radios went up on the shelves almost immediately, including a Heath HW-22A and a pair of Ameco TX-62s, one of which is a parts unit. So did something else: the tube-era thingie shown above, which has been following me around for almost twenty years. I bought it at a hamfest in the early ’90s for a dollar. The old guy who sold it to me didn’t know what it was. I bought it for the sake of the transformers inside, which were worth that much even in 1993. It turns on, lights up, and hums softly. I still don’t know what it’s supposed to do.


It’s made by Comco Communications Company, of Coral Gables, Florida. Its model number is 642-RCU. From the “RCU” I’d guess a radio control unit, or remote control unit. It has no RF parts inside. There’s an audio power amp with a 6AQ5A driving a speaker behind the grille. The front panel has a 4-pin PTT mic jack, a momentary action toggle switch marked “RADIO” above and “INTERCOM” below, with “RADIO” the default position. A hole marked “CHANNEL” with “T1” above and “T2” below is plugged. A conventional toggle switch is marked “TONE SQUELCH” above and “DISABLE” below, and beside that, an On/Off toggle switch marked “POWER”. At the center of the panel is a rheostat marked “VOLUME,” and two grain-of-wheat lamps, the orange one labeled “RECEIVE” and the red one “TRANSMIT.” A round hole the size of a panel meter is plugged. On the back panel is a fuse holder, a 5-terminal strip for spade connectors marked “PHONE LINES” and and empty rectangular knockout marked “EXT. CONTROL” from which a cut-off 4-conductor cable protrudes. That might have been a hack; the cut-off cable goes directly to the mic connector.


There are two pin jacks on the chassis (see above, just past the tan electrolytic) that say, “CURRENT ADJ. 5MA == 0.5V”. I’m guessing that the meter was dropped from the product to reduce its cost, and the pin jacks provided for service techs. To their right and a little way over is another pin jack labeled “COMPRESSOR TEST.” No idea on that one.

The tube complement is: 12AX7, 6BA6, 12AU7, 6AQ5A.

I suppose it might be some kind of phone patch, though it doesn’t look like any phone patch I’ve ever seen. The “RADIO / INTERCOM” switch throws me a little, since there’s no external connector for intercom lines. I haven’t traced the tangles under the chassis to any extent yet, so if I don’t know precisely what it does, it’s partly my own fault.

And I have other things to do. Even my voracious curiosity has its limits. If you’ve ever seen one of these or want to hazard a guess, please do!