>*** When the FCC brought these out, they calculated powers more >or less on request IIRC. In many cases, stations did not choose >to use them as at that time there were very few transmitters >which could handle powers under 250 watts at all, much less 3 >different ones.
Most every 1kw AM transmitter will drop to 250w easily. If there is no power reduction on an old tube rig, it's easy enough to set a relay to put 110vac instead of 220vac into the plate and possibly bias transformers. This lowers the plate voltage to half, which give one quarter power. At 250w, it's simple enough to make a 50 ohm RF attenuator to get the right output. It's also possible to use relays to drop in further resistance on the output to get differing power outputs. I believe the attenuator method was used for many years on KOA-850 to get the required 39kw output from the 50kw the transmitter had. They did not allow odd power settings in those days. Another method I used was to put a big Variac before the plate and bias transformers. I was able to run a 1946 vintage GE XT-1A transmitter anywhere from 1100w down to below 25w and it still sounded good. That doesn't really lend itself to automated power changes, but for operator control it worked fine. One problem is most transmitters are only type accepted at certain fixed power levels. It's not hard to get permission to run odd power levels though. The older tube rigs are much more adaptable to weird uses than the newer solid state units. If I had a situation where I absolutely positively had to have an AM station on the air, I would prefer an old tube rig. Those can often be cobbled together with some very strange parts to stay on the air. Like the time I salvaged a high current transformer out of a 6v auto battery charger to get a Gates BC-5P back on the air. It was used as the filament transformer for the modulator stage. 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]
