When I got the A.R.C. Type 12 Radio Set working, I did not have a suitable dynamotor, let alone the correct one, a D-10A. Anxious to get it going for upcoming hearability experiments, I designed a simple solid state power supply that plugs into the 3 pin connector on the rear of the R-19 receiver in place of the dynamotor. In the A.R.C. Type 12 system, that dynamotor powers both the receiver and transmitter.
The mechanical mount needs to be reworked as this is really a circuit design prototype, but the power supply runs the receiver and transmitter quite well. It puts out the required +250 VDC at +13 VDC input producing only 0.5 volts ripple.
The oscillator frequency is about 25 KHz to make the transformer and filter small and simple. It runs at 80% efficiency which is not great but I have plenty of 12V battery power available for the application..
That oscillation frequency is well above the bandwidth of the audio circuits (as well as my ears) so it is inaudible while running, either acoustically or electronically. It runs only slightly warm and not bad for a first attempt.
With the minibox cover in place the radiated switching harmonic noise is minimal and not heard in the receiver output on the VHF aircraft band.
Above: Built in a minibox, using a balsa wood “connector” and three brass sleeves for contacts to the receiver dynamotor connector. Works well enough for circuit testing.
It will also run a Command Set receiver although the voltage is too high for those radios. I will build another one with a reduced number of secondary turns for about 220 VDC or less output for those.
The key is the ferrite transformer and it uses a 3B9 core that I had in my junk box – it may be hard to exactly replicate with a different core (and material). A little experimentation will make it happen. I’ll try to find a suitable replacement from parts available these days and then evaluate a design based upon that. Stay tuned…(but not done as yet!)