[MRCA] A Note on POWERING UP AN 115VAC/800 HZ TBW power supply/transmitter ( applicable to Navy GP-7 as well )

[Michael Hanz]

That's a beautiful way to get the necessary power, Mark.  It is 
basically the way that a number of high end variable frequency AC lab 
supplies generate their outputs as well, so you're in excellent 
company.  Here is mine, resurrected from a damaged Behlman 50C supply 
with a digital oscillator readout.  The added bonus is a pure sine wave 
that has less than 0.5% harmonic distortion, so the TBW/GO power 
transformers stay cool.  And...the supply is vewy, vewy quiet... 😁

- Mike  KC4TOS



On 10/3/2023 4:25 PM, M Dittmar wrote:
> The TBW and its power supply is just a cool-looking transmitter, with 
> the big chunky components and the internal shelves, black wrinkle, 
> lots of meters and dials.  It is a thing of beauty.  However, 
> supplying AC power to the TBW power supply can be a problem, as 800 hz 
> AC power at 120 VAC at 5 amps is required for full power ( the TBW 
> also requires 12 VDC at 5 A for the keying relay and lights ). I'm 
> outlining briefly a fairly simple way to generate the 800 hz power 
> that I have been tinkering with. NO MODS on either the TBW or the TBW 
> power supply.  I can't run using the full power setting on the TBW 
> power supply, but I can reliably get 80-100 watts of stable CW out on 
> 80 meters on the 1/2 power setting of the TBW supply. This suits me 
> just fine.  I'm sure someone else could do better.  I know it is very 
> inefficient.  It is experimental.  No guarantees, but it works for 
> me.  YMMV depending on what components you can find.
>
> The stock source of AC power for the TBW power supply is the 800-1 
> inverter, hard to find and with a reputation as tornado siren as 
> well....and the inverter requires a very hefty DC power supply to run 
> it. To circumvent the whole 800 hz issue,  I suspect many of the TBW 
> power supplies were gutted and a conventional power supply built into 
> the remaining cabinet, or simply not used.  With a few minor, 
> reversible modifications to the TBW transmitter itself and a homebuilt 
> DC power supply, the TBW power supply can be relegated to the shelf.  
> I have done this with the MF version of the TBW which I use on 630 
> meter CW.  I didn't have an original TBW power supply when I set the 
> MF TBW up so I built a conventional DC supply for it.
>
> However,  a recent acquisition of an un-modified HF TBW with its 
> un-modified TBW power supply motivated me to run the HF TBW as close 
> to original functioning as possible. NO MODS.
>
> So...to make a long story short...I am essentially using a high power 
> stereo audio amplifier as an AC power source.  It is a 1200 W sony 
> stereo "XPLOD" amplifier (model XM-GTR2022), class AB ( 60 -65% eff ? 
> ) which a guy here at work gave me. I found that in bridged mode, when 
> driven with an 800 hz audio source the audio amp can generate up to 75 
> VAC rms max when connected directly to the 115VAC input of the TBW PS 
> ( bridged mode, 16 ohms output load rated ).  However if I add a 400 
> hz variac in a 1/1.4 fixed step-up configuration between the output of 
> the audio amplifier and the AC input to the TBW power supply I can 
> obtain 115 VAC at 800 hz.  So the output of the audio amp across the 
> fixed "100V" terminals of the variac, and the TBW PS connected to the  
> fixed "140V" terminals of the variac.  I can adjust the drive to the 
> amplifier from my signal generator to get the desired 800 hz AC output 
> voltage from the variac at the input of the TBW AC supply.
>
> I am using a 100 amp switching power supply from Amazon to power the 
> audio amp.  Of course appropriately sized cables used throughout to 
> handle the high current between the amplifier and audio amp.
>
> Total Key-up power draw at the 12 V 100 Amp switcher is about 230 
> watts, key down power draw at 1/2 power TBW setting about 600 watts. 
> The audio amp doesn't really get warm, but I keep a fan on it anyway.  
> Neither does the 400 hz variac.  I get about 80 - 100 watts of CW 
> power out of the TBW into 50 ohms. Good enough for me !  I tried full 
> power TBW setting but the audio amp goes into protect mode and shuts 
> down.
>
> A couple of other car audio amps I tried ( class D ) generated much 
> less voltage in bridged configuration.  Most of the class D audio amps 
> on Amazon are rated to run the high power at 2/4 ohms, and at higher 
> load resistance the power falls off RAPIDLY.  They are very cheap and 
> quite high power,  but the two samples I bought I could not get the 
> voltage swing out of them I needed.
>
> Anyway, something to experiment with if you need 800 hz AC for something.
>
> This fall I plan to power up a GP-7 using the same method.
>
> 73 Mark AB0CW
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