[BC] Re: Transmitter evolution- Comments????

[DHultsman5@aol.com]

In a message dated 10/21/05 2:18:38 P.M. Central Daylight Time,  
miltron at mindspring.com writes:

Our  FM-20B has no such thing. Was this common of earlier versions?
>  Exciter, IPA & control board are all 220. Anything lower comes from a  PS
> (i.e. fans).
> Once you kill the three phases, it's  cold.
>
> Chuck Dube
> WFCR
>  Amherst
>
 
********************************8




Is your FM20-B the transmitter that has two 4CX10,000 tubes?    Wow that is 
an oldie. But probably a first of its type.
 
 
#######  
Memories opened.....
 
 
The FM20H did have dual AC feeds, all the way to the 20H3 model.  It  also 
used 110VAC control circuits even for the remote controls.  It  had a VSWR meter 
but no VSWR protection, that was standard, until it became the  FM20K 
product.  The transmitter was an outgrowth of the FM-G  Series.
 
 I may have this mixed up but I am certain that someone will correct  me 
since I am certainly not an expert on Gates/Harris transmitters.   However as an 
old time broadcast engineer I was aware of most of the products  used and have 
used many of the one I speak about.
 
I believe what was the  the FM**-G series transmitters, 3 kW, 5 kW.,  7.5 kW, 
10 kW. and 20 kW.  all used the 4CX5000, tube to 7.5 kW.,  the  4CX10,000 
tube at 10 kW. and the 4CX15000A tube to 21.5 kW.  All of these  transmitters 
used  the Gates serrasoid exciter 10 Watt tube type multiplied  862 times to 
frequency.  These had two versions the last being the  M-6095 "Dual Cascade" 
modulator which was converted to stereo, using the  M-6164 Stereo/SCA Generator 
inserted in the multiplier stage of the  exciter.
 
The were all self contained within the same sized cabinet except in the 7.5  
kW. and above had external coaxial harmonic filters and the 20 kW. had an  
external Plate supply cabinet. 
 
The FM**H series came with the development of the TE-1 solid state direct  FM 
Exciter, I believe the engineer was Hardin Stratman.  The FM**H3 series came 
from the upgrade to the TE-3 Exciter  which was done bu Jack Sellmeyer.    
There were several  colors involved in this series of transmitters.
 
Now regarding the FM-20B....it seems that the top power for most FM  
transmitter manufacturers was 10 kW.  Many early manufacturers just added  on 
amplifiers but seldom built larger than 10 kW.  RCA built several  50 kW. FM 
transmitters one used here in Birmingham for WBRC-FM at 500 kW.  horizontal only.  They 
built several of those transmitters.  Later  they used the TV ring amplifier 
for the high powers in Michigan at the  Fetzer stations. The ring amplifier 
was driven by a standard 10 kW. FM  transmitter.
 
There was little demand and FM was not a revenue generator in most cases  
until the early 1960's inspite of being on the air since late 1947.
 
Gates and RCA both used early external combining techniques to achieve 20  
kW. using two 10 kW. final amplifiers.
 
Collins had discontinued manufacturing of their 730* Series of FM  
transmitters as had GE and Westinghouse sometime in the early to mid '50's.  Western 
Electric's FM line was sold in 1952 as part of the FTC's trust  busting.  I think 
Standard Electronics may have evolved from the Western  Electric line??????
 
ITA worked on a 15 kW. and a 20 kW. using two 4CX5000 or 10,000 tubes  within 
the same cavity.  The Gates FM20-B was similar with two tubes within  one 
cavity. I believe that this was the first single cavity 20 kW.  FM  transmitter.  
   COMMENTS PLEASE?????
I am trying to recall this information as accurately as possible so your  
help is important for to be correct.
 
Then along came the Eimac, RCA, Machlett 4CX15,000A tetrode tube which had  
the gain and dissipation to make the VHF 20 kW. with a single  tube.  Collins 
(back in the business with their 830 Series), Gates and  RCA all immediately 
came out with new 20 kW. FM transmitters for Class C  operations.  With stereo 
coming June 1, 1961 all manufacturers geared  up for new stations and new 
transmitters.  Rust, GPL, CCA, AEL,  Bauer and others entered the marketplace.
 
Eventually the triode for FM increased in power. and twenty kW. could be  
reached with three  tubes.  Usually the tube line up was a 4CX250  tetrode 
driver, a 3CX3000 or 3CX5000 IPA driving a 3CX10000 or 3CX15000.
 
All this to respond to the Gates 20B  not having two AC feeds..   I think 
I'll take a nap.
 
Dave Hultsman
Back home from the SBE National Meeting