[BC] Gates 250T...

[dynotherm at earthlink.net]

I don't recall that variation of the "T" but obviously
quite a few must have been made. The address I sent
you has the complete manual with detailed schematics
for the BC-1T with 250 W power reduction which was
the most popular model that was sold to Class IV
locals when they were permitted a daytime only power
increase from 250 W to 1 kW around 1960.

I looked through the manual, and while the overall
schematic shows 807 drivers, some of the individual
board schematics show 6BG6's. Most T's were changed
to 807's when Gates supplied new driver boards free
to anyone who asked for them. The 6BG6's were not
designed to work in a horizontal position and would
short after a brief time in service. The old 6BG6
boards were brown phenolic while the 807 replacements
were green fiberglass reinforced type so the first
question we asked anyone with a problem was, "What
color are your boards, brown or green?" If the 
answer was brown, we immediately entered an order
for the 807 conversion boards at no charge. 

Most of the "T" problems were solved by this change.

The only unusual thing (for the day) that I recall
of the "T" design was direct coupling of the 2nd audio/
driver to the modulator grids, thus it was the 
condition of the driver tubes that determined the
static modulator currents and this would confuse a lot
of guys back in the day.

You should be able to use the 1T schematics to work on
a 250 T without much problem provided it has green
driver boards in it. Many of the voltages such as
oscillator module, 1st audio and drivers will be near
those shown in the manual.

If this is a ham conversion project and the box has
brown boards in it I would recommend rebuilding the
each driver on about a 6 x 10 x 2 chassis with hand
wiring and mounting the chassis on angle brackets
with the new chassis in a horizontal position so the
807's can sit vertical for best life. Doing this will
require a couple of muffin fans to be added for good
cooling of the 807's but that should not be much of
a challenge although I wouldn't put the fans on the
driver chassis, but mount them off the side wall to
remove vibration from the drivers. The general problem
with the "T" (and the "G" that followed) was poor
cooling of the driver boards. That was the one problem
that never got fixed in the T and G series.

BTW, the green driver boards were also used in production
of the BC-500G and BC-1G. There was no 250G and the old 
'50's design 250GY design was repackaged in a square 
cornered box using all 810's in the modulator and finals.

Phil Alexander, CSRE, AMD



-----Original Message-----
>From: "Burt I. Weiner" <biwa at att.net>
>
>This transmitter uses 810's rather than 833's.
>
>Burt
>