[BC] Gates BC-1F

[Phil Alexander]

On 23 May 2005 at 9:30, Tom wrote:

> When the station got authorization to go on at night with 
> five hundred watts I was really surprised that to reduce 
> power Gates provided a big resister to put in the plate 
> circuit of the 833s.  It seemed to me that a variac would 
> have been a more practical way to reduce power but I was very 
> young and, well, you know how young people are treated 
> sometimes.  I think when a question was asked it was taken as 
> questioning a decision but my questions were asked because I 
> wanted to learn.

It would have needed a 5 kW Variac to be completely safe and
reliable because the 2.5 kV supply was what had to be varied.
For remote control, Gates normally supplied a motor driven
300 W Ohmite pot that was inserted in the 2.5 kV B+ line that
provided power for the PA and modulator output stage.

There was nothing wrong with your idea. It was a question of
cost and space. A better alternative might have been using a
tapped primary transformer and a contactor, but that would
have been a major expense too. From a practical standpoint,
the resistor worked, was easily installed and comparatively
cheap. <g> 

You have to remember that the 1F came before they days of 
1 kW day / 250 W night operation for Class IV's so not much 
design effort had been given to efficient ways of doing
power changes.

In hindsight, it might have made even more sense to leave
the voltage at 2.5 kV, pad the modulator input and drop
one of the PA tubes off line for 500 W.

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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