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

Sat Oct 22 19:44:09 CDT 2005

What I've dealt with most recently was a FM-20K with two AC feeds. Chuck,
unless you're heavily into curation of antiques as well as extreme
masochism, I would suspect that you don't really have a B model.
In the dark ages, I had a BTF-3B, which was like a BTF-5A only with lower
plate voltage. These had a 7C24/5762 driving another 7C24/5762. For 10kw, I
believe they added another cubicle with two more 5762s in parallel. I would
assume that one of these was used to drive the seven 5762s in the 25kw (not
50)  ring amplifier....
Zzzzzzzzzzzzzzz, Dave
M
----- Original Message ----- 
From: <DHultsman5 at aol.com>
To: <broadcast at radiolists.net>
Sent: Saturday, October 22, 2005 8:17 PM
Subject: [BC] Re: Transmitter evolution- Comments????


> 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
./