[BC] Gates 20B

[Phil Alexander]

On 25 May 2005 at 9:50, Mike Holderfield wrote:


> This original exciter had been replaced with a TE-3. 

An FM-1B with a TE3 stuck in it. LOL! Now there's a 
hoot. <ggg>

> I do recall 
> a Bud box with a couple of resistors in it mounted near the 
> 6146 stage had been added for swamping.
> It was still squirrelly sometimes. 

To do this right you had to work on the grid coil of the IPA
and play with the coil to get minimum VSWR to the exciter.
The swamping resistor(s) needed to be INSIDE the coil. This
was a mod that came out based on the production changes for
the IPA of the FM-1C that also had the M-6095 tube exciter.
The part about playing with the coil for VSWR was never
acknowledged in Quincy because there was no way to properly
explain it, but if you knew what you were doing and fixed
the VSWR then it became possible to get a 1B with a 6095 to
make stereo separation - for maybe all of 5 minutes. <g>
> 
> > The real problem was the B+ lead for the P-P 4CX10000D's
> > The box made the nicest 25 or 35 kW oscillator near the 
> > 80 meter ham band. No driver needed. When it did that, it
> > would take the breaker out quickly. The fix was a large
> > pi-wound RFC inserted in the B+ line where it entered the
> > PA cavity with door knob bypasses. Calmed it down greatly.
> > That was so late coming (1/68) and there were so few in the 
> > field that I don't think the fix got into a service bulletin.
> 
> If memory serves me, it didn't have the RFC mod, but 
> could of used it. This one was a '64 model.

That was found almost by accident when refurbing a used FM-20B
around the first of 1968.
> 
> > It was trying to tell you it was going into oscillation,
> > most likely. Meters jumped and KA-bam, down it went.
> 
> Exactly!

Heh, heh, obviously you've been there. A choke and a bypass or
two and you could have stopped that. It went in the BIG red
wire up at the top of the cavity and was best located on the
outside where the wire went inside. I always thought the best
way would have been to punch a larger hole and use a fair
sized feed-through cap.
> 
> >> BTW..There was also a BC-5B when I arrived there. 
> >> Nice big walk-in TX. 
> > 
> > Oh, that was a beautiful old box from the '50's made while
> > Parker owned the company. A nice art deco design, bigger 
> > than many later 50 kW boxes. If your wife threw you out 
> > you always knew where you could set up housekeeping. <g>
> 
> The porcelain light bulb fixture in the end cabinets reminded
> me of my grandma's closets. :-)

Same basic vintage of as the BC-1F, and a really great box. I 
don't think it is widely known, but although Parker remained
president until about 1967, when he sold to Harris, they 
started calling some of the shots when they bought the company,
and I've always felt that is what depressed the products
during that time. There was a drive for making the line
cheaper to manufacture that IMHO passed economy and entered 
into counter-productivity.

Phil Alexander, CSRE, AMD
Broadcast Engineering Services and Technology 
(a Div. of Advanced Parts Corporation) 
Ph. (317) 335-2065   FAX (317) 335-9037





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