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