[BC] Gates 20B

[Mike Holderfield]

----- Original Message ----- 
From: "Phil Alexander" <dynotherm at earthlink.net>
To: "Broadcast Radio Mailing List" <broadcast at radiolists.net>
Sent: Wednesday, May 25, 2005 5:48 AM
Subject: Re: [BC] Gates 20B


> 
> You had to get into the IPA and hand tune those coils for the 
> 6146 P-P stage, and I mean squeeze, twist and stretch, plus
> add a swamping resistor to the grid circuit increasing the drive
> requirement from 1 to 3 W up to about 7 or 8. That made them
> stable. Or, in pinch, you could drive the PA directly from the
> exciter, but that made it eat 6360's and had to make full power
> on some frequencies. This was true of all the FM-1B's. Mostly,
> they fixed it in the FM-1C, but the 20B used the 1B as driver.

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

> 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.

> It was trying to tell you it was going into oscillation,
> most likely. Meters jumped and KA-bam, down it went.

Exactly!

>> 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. :-)

mike