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Replace Harris FM20 Driver Section with High Powered Exciter or SS Amp

C

chriscollins

How hard would it be to replace the driver section of an FM20 with a Solid State Amp or High Power Exciter? Would the matching impedance be a problem? Has anyone done this?

Seems like it would save money and add some reliability, with the driver tubes out of the equation.
 
I think the IBS group was using Ptek 500 watt unit in some xmtrs replacing the dreaded tube drivers on an FM in the Delta.so apparently it can be done.
 
Ah, no.

I had a 2.5H3 (since shipped off to Columbus, Indiana) and still have the Harris 10K. Very different critters.

The 2.5H and 2.5K (similar transmitters, the original H series used a TE-3 exciter, the K used the MS-15 exciter) had 50 ohm inputs into the final. The IPA was little more than a buffer amp. The Ms/MX exciter could drive the final to about 1200 watts; I used a BE FX-50 to drive my 2.5H; about 25 watts was enough to drive the transmitter to our licensed TPO of 2450 watts. Much more stable as well, compared to the original tube IPA.

There was also a FM3K and and FM5K; as well as 3G/H and 5 G/H series. Long time since I've seen either models. These were all three-phase boxes, but I don't remember how the the IPA was coupled into the final. I'm thinking the 3 was similar to the 2.5K, hence could easily use some sort of outboard solid state driver.

The 10K, unfortunately, has a different configuration, the 4CX300A is coupled directly into the grid of the final. Hence the problem that has developed--the manufacturer no longer makes this tube. Considering this box is around 25 years old, there is little point trying to sink a lot of hours and money into working around this problem. I was able to find several new ICAS 4cx300A's at RF parts; but still plan to replace this transmitter in the next few years.

I suspect the 20H series would have a similar problem.

The HT series, which came out in '88--'89, used a solid state IPA, and is a completely different design.
 
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