[ARC5] JFET in ARC-5 TX Oscillator socket

[Robert Eleazer]

I have sent scans of the ARC-5 solid state oscillator article to David Ross and he is going to put them in a new Command Set section of his Real Radios Have Motors website. But until we get that done here is some more info on the conversion from the June 1967 magazine.

They used a U-112 FET with original parts except for a 0.01mfd cap from D to ground and a 1 to 2.5 mh RF choke between D and the power supply. Power supply was 10 volts. And this was using a positive ground approach so the B+ was in reality B-. 

HOWEVER, he says that without any component changes, just attaching the FET leads to the tube cathode plate and grid pins of the tube socket the oscillator took right off with no component changes, just like Ian says. And he tried all of the HF Command Set transmitters and it worked with all of them.

The FET fed two 2N3638 bipolar transistors which were used as a Class A buffer and a Class C amp. The power input to the final was 1 watt, which was far more than required to drive the Gonset he was using, but the bipolar final needed a heat sink.

By the way, the guy in 1967 put the transistors in the hole in the middle of the three tube sockets, which is pretty cute, but to me it would seem to be easier and probably better from the RF standpoint if you just soldered them to the sockets on the underside - unless you need cooling for the power stage.

Happy 4th!

Wayne, WB5WSV