[Milsurplus] 800 cycle transmitters

[Bruce Gentry]

If the TBW was a transportable rig, was there a lightweight 800 cycle 
generator to power it?  In those times, Homelite made a 180 cycle  
portable gas generator for powering tools. Modifying the design  for the 
higher frequency would not have been  difficult.

      Bruce Gentry, KA2IVY

On 11/16/17 7:13 PM, Richard wrote:
>
> The TBW was an advanced base transmitter designed to be carried ashore 
> in a small boat by a few sailors, so weight was a primary concern.  
> The 800 cycle power supply and modulator weighs 68 pounds, and would 
> weigh about 240 pounds if 60 cycle.  They started with 800 cycle power 
> in airplanes in the 1930's, then changed to 400 cycles in the 1940's  
> because of reactance problems with 800 cycles - 400 cycles was easier 
> to work with. There is indeed no advantage to high frequency power 
> other than less weight, and as Ray points out, changing to 60 cycles 
> is not a trivial problem. Well, it's cool using power frequency for 
> MCW, and one marine transmitter used 500 cycle ac picked off the 
> dynamotor for plate modulated MCW.
>
> Richard, AA1P
>
>
> On 11/16/2017 03:19 PM, Ray Fantini wrote:
>>
>> 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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>
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