Bob W7AVK wrote:


If you have the room and technical ability might consider converting a
salvaged AM broadcast transmitter. They are available as most stations
are removing them to upgrade to much more efficient solid state units.

Yup - a Harris MW1 would be ideal... save for the power transformer(s)
nearly everything else can be either hand made (coils, etc.) or bought
off the shelf (transistors, etc.- including the PAs). The "output" unit
consists of 13 identical RF modules twelve as PAs - one a driver. They
"normally" run a 83W each - if one dies - the matching network
effectively isolates it - the drive to the remaining PAs "steps up" -
and it stays at a KW. One of easiest to maintain transmitters around
(from both layout - and parts availability). PA B+ is (IIRC) something
like 70V - the modulators consist of two sections - one that passes the
70V (i.e. saturated at 0% modulation) - or ramps down towards cutoff
with negative modulation- the other section of the modulator is tied to
+140V - and as positive modulation is applied - it overrides the 70V
rail - and up it goes pulling the PAs with it. Capable of 110% positive
modulation if everything is up to snuff. Each of those 13 identical PA
modules includes it's modulator (both sections). Very efficient for an
AM transmitter.

best regards...
--
randy guttery

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