[BC] The Worst Transmitter

[Phil Alexander]

On 19 May 2005 at 14:16, Dave Hultsman wrote:

> But remember the early tetrodes used in those monsters were 
> pretty difficult to tie down.  RCA, Gates and Collins had some pretty scary 
> tetrode boxes back in the early '60's.  Getting control of neutralization 
> and byp[assing the screen was a mess.   Collins finally solved the problem 
> with oscillation by grounding the screen and pull the cathode below ground. 
> No screen by passes and ground was pretty stable.

The true problem was the basic 4CX5000A according to the original Eimac sheet
had a MAXIMUM useful design frequency of 30 (!) MHz. It also had a G-K cap of
115 pf. RCA started the whole thing by putting a 4CX5000A the BTF-10D and
series resonating the grid capacity to get power into the tube. Then, the
world followed.  IMHO, the earlier GE's were better boxes because the 7D21's
and 8D21's used in them actually were designed for the frequencies used.

Phil Alexander, CSRE, AMD
Broadcast Engineering Services and Technology 
(a Div. of Advanced Parts Corporation) 
Ph. (317) 335-2065   FAX (317) 335-9037





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