Re: [IRCA] WCSL-1590 10 kW or 1 kW

["Craig Healy" <bubba@xxxxxxxxxxxxxxxxxxxx>]

>*** 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


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