[MRCA] ARC/RCA Dayton Project

[Ray Fantini]

Progress on the ARC/RCA project. Receiver is all up and working without issues. Last night had the transmitter up and running at around ten watts but the modulator is a little week and may reduce the screens on the 1625 tubes to bring the power down to around five watts. Wonder if I could just go with one tube? The MO for the ARC-5 is good and strong and what surprises me is that there is no chirp or drifting when keying the transmitter and its performance is far better than I expected it would be. Can see why these were so popular with Hams back in the day.  Too bad I can't do CW because this would make a nice little CW station.
Am running 330 volts on the plates of the 1625 tubes and 165 on the screens. Did not check the plate current yet but know that I am consuming about 10 MA on the screens at power and will be looking at plate current tonight. The entire system draws about five and a half Amps in receiver with two amps used by the receiver, one by the Narco and the rest by the transmitter filaments. May put a switch on the center part so I can kill the transmitter filaments when not needed being that will save about two Amps. Also was thinking that I can use a switch that will power just the MO in the transmitter so I can spot the transmitter on the receiver.
The receiver works well on +165, maybe better then what I assumed would be the B+ of +250 and have to wonder what the original B+ would have been?  Still have to work out the T/R system and speaking of relays and such the narco was designed so that when the ground ring of the microphone was put to ground the internal audio amplifier in that unit would come on and drive a local speaker but if you lift the microphone from its hook the internal speaker circuit shuts itself off. Was thinking of using the internal amplifier in the narco for added audio but decided that the audio from the receiver and its 42 tube output is strong enough.

Ray F/KA3EKH
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