> Assuming a pair of 833s (e.g.) in a push-pull configuration: Now that > you replaced one, you should replace the other as now they are > probably unbalanced. > > Since that's probably not easy on the station budget, I'd suggest > that you try to increase the negative feedback around the modulator.
Often in transmitters using a pair of 833A's in p-p, the driver section is a problem. Some years ago I had a late 1940's GE XT-1A to repair. It used a couple of 845's as audio drivers, and the driver transformer quit. I happened to have a fairly high power UTC transformer with around a 30 ohm primary winding, and a split winding of about 8,000 ohms or so on the secondary. I put a Marantz solid state stereo amplifier on the primary, using the two channels out of phase as a balanced push-pull output. I had a small transformer of about 600 ohm to maybe 10k ohm at the input to go from balanced to unbalanced out of phase at the amp input. The split winding of the secondary allowed me to use the existing feedback ladder and modulator bias adjustment pots. When I got done, the transmitter sounded much better than original. The Marantz amp was mounted in a rack in another room. Never had any feedback issues, which was lucky. That transmitter also had a very large 220v Variac that fed the main power supply and RF tube bias circuits. It could be dialed from over 1,000w down to under 25w and still sound very good. It was at WRIB and taken out of service in the late 80's. Anyone with a QSL from before roughly 1989 heard that transmitter. I might have a couple of used but still good 833A's around somewhere. Great old bottles, they were. Craig Healy Providence, RI _______________________________________________ IRCA mailing list [email protected] http://montreal.kotalampi.com/mailman/listinfo/irca Opinions expressed in messages on this mailing list are those of the original contributors and do not necessarily reflect the opinion of the IRCA, its editors, publishing staff, or officers For more information: http://www.ircaonline.org To Post a message: [email protected]
