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[OT] Broadcast Engineering (was:Re: Google Earth)



On Monday 14 January 2008, Gene Heskett wrote:
> I still do the transmitter cuz Dave never saw a vacuum tube till he went to
> work for us about 11 years ago now.  

:-)

Former employment involved a Doherty linear running a pair of 4CX15000's as 
carrier and peak, driven with a 30W solid state exciter, making 
10KW+125%-100% AM into a two tower DA-N.  Also involved a 3rd harmonic-driven 
RCA BTA-5T with a single 5762 in the final, modulated by a pair of 
3CX3000F1's (this transmitter was later replaced with a Harris DX-25U; in 
fact, I was on my way to this station to work on the DX-25U upgrade when the 
South Tower was hit on 9/11) into a 4 tower inline DA-N (and, of course, the 
highlights of the year were the twice annual phasor rocking expedition....).  

And then there was the BTA-5F which was supposed to use three 892R's, but, due 
to the extreme cost and shortage of that tube (rebuilds, assuming a 
rebuildable dud, were over $3600 per, in 1990, and new ones were simply not 
available for any price (the last they actually quoted for purchase were over 
$10,000 each; I've not checked recently to see if this 50-pound-plus beast 
was even still available at all)) the previous engineer modified it to be 1KW 
only using a pair of 833's mounted to a spruce 2x4 sitting on top of the 892R 
modulators' air stacks.... 

Working with glassfets (firebottles, whatever you want to call them) has 
always been fun.  Not terribly reliable (compared to a Nautel ND-10 I babysat 
for years; from 1989 until 2000 the only parts that had failed were one power 
FET and a crystal; after that a couple of modules went due to FET failure, 
but still....) (But, then again, that Continental 316F Doherty had the same 
pair of 4CX15000's from 1984 until 1998; the 164 amps through the filaments 
finally caused the filament fingerstock in the socket to carbonize, causing 
an arc that breached vacuum integrity)..... 

But I digress....
-- 
Lamar Owen
www.pari.edu


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