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
