The Temco RA-150 (late 1940s)
The Temco (stands for Transmitter Engineering
Manufacturing Company) RA-150 is a blast to operate, especially if you're
into "old buzzard" long winded style transmissions. If you've wondered why
some people make 10 minute long transmissions this rig will explain why.
It's necessary to key the oscillator first and then the plate supply to
transmit; and do the reverse to receive again. Make no mistake about
operating PTT here. You can actually master it with a little practice, and
the Temco people made it easy for you since the transmitter has it's own
"wired" remote control box attached to a 6 foot cable - neat!
The tube lineup is a single Eimac 4-65A tetrode
modulated by four 6L6's in push-pull parallel. It will make just about 100
watts output on the lower bands and a little less on 15 and 10 meters.
Each band has it's own 1614 (a metal variant of the 6L6) oscillator, and
it's necessary to change grid coils when changing bands. The internal VFO
does not give a direct frequency readout, which is a little different than
most ham rigs. You instead use a supplied calibration chart to determine
your operating frequency, or else an external frequency counter to
measure your transmitting frequency. Even simpler, I tune mine to zero
beat into my receiver with the oscillator on.
Transmit audio is “communications quality” and
usually a bit better than that when used with a crystal element D104 or
Turner 22X crystal microphonium. The secret is the high impedance of these
two mics which allows improved audio response.
The Temco weighs about 200 to 250 lbs so be prepared
to have a helper help you move it around your shack if you plan to
relocate it.
One very positive note: Most of the caps are oil
filled with the exception of the audio coupling caps in the speech amp.
You'll probably be able to rekindle the power supply just by bringing it
up on a variac. B+ is handled through a pair of 866-A’s. Everything in
the transmitter is easily serviced through the rear cover and each
"module" slides out to facilitate repair. Everything seems to be made of
the highest quality material at the time (1947-1948).The optional FM unit
(tried it on 10 meters coupled to a pre-war Hallicrafters S-27) works very
well.
If you're lucky enough to find one of these
transmitters it'll be a forever "keeper" in your shack.
Mod-U-Later,
Joe Cro N3IBX
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