[MRCA] ARC-5 RCA Dayton project

[Ray Fantini]

A 20K 5 watt resistor between the plate and screen grid did the trick. Increased the modulation and simplified wiring. This means that the +165 is only used for the MO so I put a switch upstream that will allow the MO to be powered without keying the transmitter so I can "spot" the transmitter on the receiver. The idea being I can hear the other traffic on 3.885 at the event and set the receiver and then set the transmitter by spotting it on the receiver.
I did notice that the output loading has big effect on modulation and distortion. Transmitter sounds best loaded at half power around five watts but has noticeable distortion at nine watts. Best audio is with loading at 35 Ma for 5.5 watts, that's an indirect power of about 11.5 watts and getting a little over 5.5 out gives me an efficiency of around 50%. Not bad for something built out of seventy year old technology.
The whole system consumes just under 6 Amps @ 12.0 volts so that's about 72 watts to produce 5 watts of RF power or 2 watts of audio from the receiver by today's standard of Yahoos and Kenwoods that's a tremendous waste of power but there is no substitute for the joy that's derived from a transmitter and receiver that's using twelve tubes and designs from 1938, next week that will be 80 years ago!
If anyone is interested I can post the updated finished schematic or additional pictures and may have to do another YouTube for this also. Still have to work out the T/R relay and maybe a frame or box for all this to fit in. just hate to put any kind of cover over the receiver being that its layout and construction is in my mind a work of art.

Ray F/KA3EKH

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