RICHARD GEORGE wrote: > I have over the years built several low power AM transmitters. I would like > to build something a little bigger say in the 400-500 watt plate modulated. > I have been kicking around the idea of using one of the solid state > amplifiers made for car audio driving a reverse connected audio transformer. > I have seen these audio output transformers available in the 200 watt range. > I understand that the RF output stage would have to be designed to fit the > impedence of the output transformer. Does this sound like it could be done? > Well, sort of...
The problem will be if you run the RF PA plate supply current through the modulation transformer (or modulation transformer wannabe) secondary. The transformer then needs to be designed for an unbalanced DC current flowing through one of the windings, because the core is magnetized by this current, leaving less effective core for the audio signal riding on top of it. Don't know of the output transformers you are talking about are single-ended (unlikely at 200W) or push-pull. If single-ended, you can run a DC current through the winding to the extent it was designed for. If PP, then no, you can't, you can have a modulation choke pass the DC current to the RF PA, and capacitively (AC) couple the transformer secondary to the choke (Heising system). But then, you need to find a suitable modulation choke, which could be as difficult as finding a suitable modulation transformer. Chokes and transformers designed for an unbalanced DC current have all the E and I leaves lined up, and have a precise air gap separating the two stacks. Transformers designed for no DC current, or DC currents that cancel as in a PP winding, have the E and I sections interleaved. 73, -Larry/NE1S ______________________________________________________________ Our Main Website: http://www.amfone.net AMRadio mailing list Searchable Archives: http://www.mail-archive.com/[email protected]/ List Rules (must read!): http://w5ami.net/amradiofaq.html List Home: http://mailman.qth.net/mailman/listinfo/amradio Post: [email protected] To unsubscribe, send an email to [email protected] with the word unsubscribe in the message body. This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
