[AMRadio] Stock or modify? BC rig "value"


Phil Galasso k2pg at worldnet.att.net
Sat Jun 3 12:43:04 EDT 2006


----- Original Message -----
From: "Jim Wilhite"
>
> Some considerations about moving a broadcast transmitter to 75 or 40 that
> one should make is the design of the RF deck.  Keep in mind that lead
length
> from the tube to the blocking capacitor, from there to the tune cap and on
> to the coil will exhibit additional inductance beyond the coil
properties..

The Collins 20V series will work on bands up to and including 20 meters
without making radical changes in the output tank. It was designed by
Collins for use up to 15 MHz by special order. Changing coil taps and some
capacitors in the tank would accomplish that. The plug-in tank circuits in
the lower level stages would have to be rewired for operation on bands above
160 meters and the 6SJ7 buffer stage would be converted into a frequency
multiplier, according to information published by Collins. The 21E/M
transmitters are also capable of operation up to 15 MHz.

The Gates transmitters are totally unsatisfactory for 40 meter work and
marginal, at best, on 75. Best to leave them alone and just enjoy them for
what they are...a fine 160 meter rig! For the amount of work you would need
to do to modify those transmitters for 40, you'd be better off just visiting
WA1QIX's Web site and building a nice Class E rig. As a bonus, the Class E
rig uses less electricity and runs cooler.

Phil K2PG




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