[BC] Remembering our "Ol' Bessies"

[Ron Nott]

Yes, a pair of 4CX5000s as modulators in a 5 KW transmitter is overkill, but 
there is also a Collins 820F that is 10 KW output.  The two boxes were 
almost identical except that the F used two 4CX5000s as the PA, and of 
course the power supply was beefed up to handle it.  The metering was 
changed to accomodate the difference in powers.

There is a weak link in both these otherwise fine transmitters in that there 
is a filament voltage regulator with a motorized Variac that uses two pilot 
lamp bulbs as legs of a balanced bridge.  If one bulb burns out, the 
filament voltage goes low, but if the other bulb burns out, filament voltage 
goes near 8 volts which can drastically shorten the life of the tubes.
ron

> A pair of 5000's in the audio is overkill... I'll bet those tubes lasted a
> good LONG time, tho! That sounds like a much better design than the Ol' 
> Bessie I
> used to tend to, a CCA AM5000D!
>
> It used a pair of 4-1000's for the audio, and a 3CX2500 for the final. 
> Yes,
> it did 5Kw just fine... but couldn't get much over 105% positive mod 
> without
> starting to fall apart. The plates in those poor 4-1000's were constantly
> glowing *orange* with audio!
>
> In the ealry/mid 90's, my then-Engineer and I modified the thing to use
> 4CX3000's for modulators. The modulation didn't improve nearly as much as 
> had been
> hoped. Still, gone were the days of replacing those 4-1000's every 12-18
> months! (Good thing WFIF was a Daytimer!) That last set of modulator tubes 
> wasn't
> even showing signs of going soft when "Ol' Bessie" was finally put out to
> pasture, about 5-6 years later!
>
> Willie...