[Milsurplus] PRC-74 questions

[Ralph Hogan]

Bob,

Here is an outline of a mod that Jim Karlow uses for LSB conversion.

"The conversion works by shifting the IF injection from the frequency
generator module from 1750 kHz on USB to 1747 kHz for LSB. When used with
the existing 1750 kHz IF filter, this will allow the lower side band to be
received and transmitted on the PRC-74. In order to provide correct dial
readout in the LSB mode, this conversion also includes a modification to the
frequency synthesizer. This modification allows the synthesizer frequency to
be "pulled" up 3 kHz in the LSB mode to compensate for the injection
frequency shift to permit LSB reception and transmission."

Ralph W4XE

-----Original Message-----
From: milsurplus-bounces at mailman.qth.net
[mailto:milsurplus-bounces at mailman.qth.net] On Behalf Of Robert Nickels
Sent: Wednesday, October 07, 2009 6:56 PM
To: Mil Surplus List
Subject: [Milsurplus] PRC-74 questions

I've been able to get my newly-acquired PRC-74 working on receive at 
least, after replacing a bad "varistor" in the 9 volt regulator 
circuit.  Anyone know what these parts are, exactly?  With a nominal 
resistance of 300 ohms, they're not what I think of when I think 
varistor (i.e. MOV).

If anyone has experience working on these radios I have a couple of 
questions related to the mechanical linkage between the Mhz selector and 
RF unit.  The front panel is pretty cramped and complicated, and I'd 
like to make sure I'm on the right track.

Also - is there any info on LSB conversion?  It seems that this was done 
to my unit.

Thanks and 73,
Bob W9RAN