---   The Final Power Supply   ---




Well, AM enthusiasts, vacuum tube enthusiasts, and 1930's transmitter technology enthusiasts, I'm down to working on the second to the last deck of BigRig. This one is sort of a combination - it's the high voltage power supply for the final amplifier, and the deck also contains much of BigRig's control relays and circuits.

I've made a few circuit changes in this deck, primarily in the way the circuit fusing is configured. The controls will remain as they were, just the way it is fused has been changed. I'm thinking of also changing the output bleeder resistor, but I haven't yet decided for sure. The present bleeder is a 50K 100 watt unit. It's visible in the under-chassis photo. Yet, if the supply can generate about 2.2Kv, and I seem to remember it does, then the dissipation in the bleeder is uncomfortably (for me) close to the resistor's power rating. Thus, I'll either change the resistor to 100K or opt for a larger resistor. Under-chassis real estate seems to be a mite scarce, so I'll probably stick with the 100w resistor and change it to 100K. Because of the large series inductances used in the supply, it has relatively small capacitances, and so the 100K will discharge the capacitors quickly enough for good safety.

When BigRig was originally built, there were two indicator lamps on the front panel of this supply. The green one showed filament power being on, and the red one showed HV being on. The two lamp assemblies each used a 110 volt candelabra bulb, which for some reason, I didn't like. So, when the OM said ok, I replaced the two of them with a "modern" (for 1955) pilot lamp assembly of an industrial style, which ran from 110v but had a tiny 6-volt transformer built into it, and ended up running a #44 lamp. One can see those assemblies in the photos. Also, I added a third one, a yellow ont, to indicate the "on" state of the low-voltage DC. Note though, that the jewels for those assemblies are much the worse for wear. Apparently over the 40 years that BigRig lay on its back on the damp basement floor of my friend Orlando, he failed to go to the basement each day and wipe the corrosive dirt off of my lamp jewels. He'll hear from my attorney. I've been quite unable to find replacement jewels for the Square D lamp assemblies, so I may have to replace them with a different brand.

I also gotta figure out how to handle this thing when it's all back together. When I did the CG calculations for the rack, and I weighed each of the decks, this one won hands-down at 76 pounds. Funny how that was never a problem when I was 15, but when I get this deck up and running, I'll be looking for a young and healthy ham with a strong back, to help me mount it into the rack.

Well, that's about it for now. I've got to get to work on this deck.

Today, August 30, the final power supply has been completed! Oddly, this deck was the most complex and the most time-consuming of them all. It took a lot of hours just to document this thing, because the deck not only houses the high-voltage power supply for the final amp, it also houses all the control circuits for the transmitter. Then, it took a long time to build it, too. I had to build it with the power transformer in absentia, and then add the transformer when all else was done. The deck is just to heavy for me to handle with the power transformer mounted. Well, all's well that ends well, I guess. I got it all done and photographed without a hernia and without a heart attack. Soon, children, soon - the W8VR AM signal will be on the air - perhaps even by the end of the year. Anybody out there with a real AM transmitter interested in being BigRig's first contact of the new era?

Well, gotta run. I can't sit around here all day playing with a computer - I gotta final to build!





August 30, 2009. 73 de W8VR






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