[BC] Harris FM10 250 driver

[Mike McCarthy]

  With a SS IPA, the IPA's metering is moot...at least as far as the TX 
is concerned.  All you care about are the PA's parameters and an 
overload interlock with the new IPA.

The folks I spoke with are looking into a "bolt-on" system which 
essentially replaces everything in the IPA cavity with a transforming 
and rotating network to allow the 50 ohm system like on the newer TX's.  
And yes, they know the transmission line connecting to the PA will be 
phase sensitive.

I won't argue the TX's weaker points are it's age and control ladder.  
And only a TX whose wiring harness and overall chassis are in good 
condition should see this modification.

I would however argue the type certification would remain intact as the 
PA and harmonic filtering are not changing.  And because either the 
exciter and/or processor would likely be changed, the TX would need to 
be re-proofed regardless.  So while the OEM system certification would 
be invalidated, the field proof would re-cover that aspect.  Moot point.

MM

On 11/16/2010 1:37 AM, Jerry Mathis wrote:
> If we're talking about the FM-10K transmitter from Harris, frankly, I wouldn't put a lot of money into one of them. While the tube cavity and output network are sound, the rest of the transmitter is, shall we say, flaky by modern standards. Relay control and monitoring, and the relays are getting hard to come by. The control circuitry is powered by 240 volts--and only fused on one end! Even the overload control potentiometers are obsolete. And the transmitter metering is absolutely pathetic. For instance, the only monitoring of the problematic 4CX300A tube is cathode current. You can't monitor grid current, screen current, screen voltage, nor plate voltage. Even the final PA tube's screen and grid parameters are not metered. One of the worst transmitter designs I've ever seen. The FM-##H model was the same, BTW.
>
> It would be impossible for a SIMPLE retrofit to introduce a SS amplifier into this transmitter, because the IPA output/PA input are directly coupled and not transformed down to 50 ohms in and out. Any such modification would invalidate the transmitters' FCC acceptance, I'm sure.
>