[Amps] Trying to locate amplifier

Fuqua, Bill L wlfuqu00 at uky.edu
Sun Dec 5 23:23:30 PST 2010

Perhaps it was a GE. 
I can't remember if it has two big dials or just one. One control went to the swinging link coupling. 
But it did have a pair of forced air cooled bypassed EF Johnson sockets for either 4x150 or 4cx250 tubes.
bill wa4lav

From: Glen Zook [gzook at yahoo.com]
Sent: Sunday, December 05, 2010 11:21 AM
To: Amps at contesting.com; Fuqua, Bill L
Subject: Re: [Amps] Trying to locate amplifier

Motorola may have built such an amplifier for the military.  However, for the commercial FM two-way market the Motorola lowband and highband amplifiers used 8650A tubes which are the conduction cooled versions of the 4CX250B.  General Electric made thousands of lowband and highband amplifiers using the 4CX250B that had dials similar to those made by National.

Motorola did make a 450 MHz amplifier using a single 4CX250B rated at 100 watts output.  However, with the power supply that Motorola used, plus "something" in the actual physical construction, when tuned for 100 watts output the amplifier would make that for less than a minute and then drop back to a steady around 90 watts output.  I have one of those amplifiers that I tuned down to 432 MHz (tune down without any problems) and bypassed the external bandpass filter.  Without the filter (the amplifier is still "clean") it makes about 150 watts output on CW.  I haven't used the amplifier for a while but need to redo the bias so that I can use it for SSB as well as CW.  The original design is Class C for FM operation.

Glen, K9STH

Website:  http://k9sth.com

--- On Sun, 12/5/10, Fuqua, Bill L <wlfuqu00 at uky.edu> wrote:

Many years ago (late 60's) I converted an amplifier which was a low band VHF to 20 and 15 meters. It had a pair of push pull 4CX250B or perhaps 4X150A tubes (no tube came with it). I parallel connected the tubes, both halfs of the plate capacitor and used the whole coil. I also use a dual 365pf variable to convert it to a PI network. I first used it for a while with 4X150s until I came across some cheap 4CX250B's.

In any case I am looking for another one. It had some vernier dials National on the front as well. Does anyone have an idea what this was? I believe it was made for the military by Motorola.

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