Far as I know, more is always better, as long as the inrush current of a discharged capacitor does not cause problems with the rectifiers or choke.
I use step start, a time delay relay of about 1 second that puts a resistor in the primary, say about 10 ohms, whatever gives about 1/2 voltage at the end of a short wait (one second), then the relay shorts the resistor out. I think my 813 rig runs about 70 uf at 2000 volts, with 4 12kv 1 amp brick diodes in center tap to ground setup. The bricks can handle 15 amps for a very short time. I have never blown one out... In the homebrew stuff, I always use separate power supplies for the modulator and rf deck, with a swinging choke and the extra capacitance in the mod power supply. I don't think a lot of extra capacitance does much in the rf power supply. If you actually intend to use the globe chump, I would run it easy, its not a robust transmitter. I might change the cap to something like a 20uf, I don't think you will get loads of low end bass out of the transmitter anyway, where the energy storage pays off the most. You likely don't want to push the mod iron much, trying to force a lot of low frequency through it might blow it out. I would not try to pass anything lower than about 150 to 200 hz through it.... When I was young and stupid (now I am old and stupid), I was running tests on my 30K1, putting a signal generator into it, setting the mod at 100% at 1khz, then reducing the audio frequency and noting the -3db points. When I got down to about 40hz, the mod transformer blew out. DUH! There is a lot of power in low frequencies, so be careful. I don't sweep rigs at full power anymore, or generally sweep them at all. Brett N2DTS > > I wish to avail myself of the knowledge here: My Dad, W5JHJ, > has a WRL > Globe Champion 350 and is the original owner. He's > maintained it and it > works well, but I wonder if a mod he made years ago was a > good one. Like > most AM transmitters, it uses a choke-input PS design. I > cannot recall the > input choke values, but do recall that it incorporates a > swinging choke and > that the filter capacitor was originally quite small (2 uF, I > think). that > capacitor failed some time ago, and as I was looking at his > documentation > saw that he'd replaced it with something like 40 uF. > > On the list, I recall scrolling across a few postings (now > lost) that said > something about how these PS should be designed. There, I > thought I saw > something along the lines of it being possible to have too > much filter > capacitance. Did I get that right? If so, what's the > symptom of too much > filter capacitance in a choke input filter? > > Kim Elmore, N5OP > Kim Elmore, Ph.D. > University of Oklahoma > Cooperative Institute for Mesoscale Meteorological Studies > "All of weather is divided into three parts: Yes, No, and Maybe. The > greatest of these is Maybe" The original Latin appears to be garbled. > > _______________________________________________ > AMRadio mailing list > AMRadio@mailman.qth.net > http://mailman.qth.net/mailman/listinfo/amradio
