[BC] getting the right tube combinations

[Wayne]

I have to agree with both viewpoints to some degree.
The use of a pair of 4-400's in an 70% efficiency mode did not leave much 
design room.  The local availability of the tube, and the ease of tune-up of 
a tetrode were probably the driving factor for that choice.  The QY 5-500 
was a better tube but required a different tube socket, and filament 
transformer.
Eimac made a 5-500 but it was terribly expensive.
Most tube deaths are caused by inadequate air flow, high temperatures and 
improper tuning.
The 4-400 Data sheet specified vertical mounting.
>From a sales point of view, Broadcast transmitters do not present a huge 
market that would inspire futuristic design trends.
Modern Transmitter designs move slowly in order to keep up with the 
technical abilities of the service industry.
Wayne Woollard

----- Original Message ----- 
From: "Jerry Mathis" <thebeaver32 at gmail.com>
To: <broadcast at radiolists.net>
Sent: Saturday, August 05, 2006 9:45 PM
Subject: [BC] getting the right tube combinations


> On 8/5/06, Jim Tonne <<mailto:tonne at comcast.net>tonne at comcast.net> wrote:
>
>
> I think the use of the 4-400 etc was based on the thought that
> a simple driver could be used;  as I recall it was just an 807.
> The 833s, while remarkably robust and tolerant of improper
> loads etc did require a hefty driver.
>
> ....Which Harris DIDN'T do either. BC-1G and similar 1 KW, RF drivers are 
> a pair of 807's. It worked, as long as the 807's were in top shape. As 
> soon as they started to weaken, you started loosing positive modulation, 
> until finally you couldn't even make full carrier power. Of course, they 
> seldon got that weak; the horizontal mounting of the 807's caused the 
> grids to sag, and they usually shorted out and blew the PS fuse long 
> before then.
>
> I know I've said this before, but the best 1KW AM transmitter I ever saw 
> was the Raytheon RA-1000. 833's driven by a PAIR of 813's on the RF side, 
> and by 845's on the audio side. You could run the 833's forever in that 
> transmitter, it seemed.
>
> -- 
> JM
>
>
>
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