[BC] FM Grounded Grid Triodes & FM Tetrodes

[Dave Hultsman]

RCA may have pioneered tetrode FM power amplifiers,  but their early FM transmitters used ground grid for 3,5,10 kW.  and even the later few FM 50 kW. all using the 5762 finals.   The 50 kw. used the 7 triode tube ring type final amplifier used in TV aural amplifiers.   The original RCA 50 kW. FM transmitter of which, I believe, there were three made, I seem to recall used three triodes in parallel in the output stage.   WBRC-FM and a station in Madison Wisconson used that transmitter in the early FM days.
 
In the rebirth of FM in the late '50's Eimac & RCA came out with a complete line of new ceramic triodes which were used by many manufacturers,  AEL, Bauer, CCA, CSI.   ITA as I recall started out using the tetrode tubes, 250 Watt- 4CX250B; 1 kW. - 4CX-1000,  3 -7.5 kW - 4CX-5000A,  10 kW. - 2-each 4CX-5000's.
 
Collins late '50's to get back in the FM market had ITA build transmitters to their specifications and a diffent color.  These were all tetrodes.   Then Collins designed their own Ground screen tetrode line in the early '60'  called the 830 Line.
 
The used of tetrodes by RCA was when their tube division began manufacturing 4CX5000's and 4CX15,000 tubes as I recall.   Prior to that time their FM transmitters were all grounded grid triodes.
 
Dave Hultsman
Worcester, MA 
 
In a message dated 11/10/2010 12:18:19 P.M. Central Standard Time, RichardBJohnson at comcast.net writes:
>Even though RCA pioneered grounded-grid amplifiers for television, their FM transmitters were all grid-driven tetrode amplifiers,