[Milsurplus] 800 cycle transmitters

[Ray Fantini]

All this talk about how wonderful the 800 cycle power supply is to use with the TBW or GO family of radios makes me wonder why that was ever chosen in the first place. I have owned and operated a TBW and one of my first actions was to build an AC power supply separate from the transmitter. Not as easy a task as it would first appear being that all the filtering for the TBW is designed for 800 cycles and way too small for 60 cycles so none of the filter capacitors or chokes are useable in a 60 cycle retrofit. Original keying of the transmitter interrupted the primary AC feeds to the HV transformer and due to the small value of the power supply filters there was a minimal amount of chirp but when you go to the larger filter networks required for 60 cycles you quickly discover the time constants for your filters causes real issues, so much so that I had to build bias supplies into the transmitter to cut off the driver and oscillator upon key up. And then there is the issue of A2 modulated CW that used raw 800 cycle AC to modulate the suppressor grid of the 803 but being A2 is not permitted on the Ham bands that was not a problem.
I am going to propose the only two reasons that such a high frequency was ever used was due to the fact that it provided a good source of modulation in the A2 mode as a primary reason for 800 cycles and that the secondary reason was that at 800 cycles they were able to use smaller transformers and power supply filters then if it were run at 60 or 400 cycles. Other than that I see no advantage to that high a frequency for a power supply.
Maybe it was a weight concern? Going to make another assumption that the TBW was a striped and light weight version of the shipboard TDE transmitter, similar design around an 803 tube and suppressor modulation but the TDE used a huge motor generator or 60 cycle AC power supply. Would be curious to know what came first? I am thinking TDE and then TBW.

Ray F/KA3EKH
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