[Amps] 4CX250 IMD

[Radio WC6W]

Hi Carl,
  Check the 8904/4CX350FJ.  It has superb IMD specs
and will fit the socket.  A retrofit will be required
for the heater supply.

73 & Good evening,
  Marv WC6W 

http://wc6w.50webs.com/


--- jeremy-ca <km1h at jeremy.mv.com> wrote:

> According to my full size Eimac manual ( the yellow
> one with the multi page 
> spec loose leaf sheets) the only 4CX250 style tube
> with decent IMD is the 
> 4CX250R/7580 which was used in a lot of military
> equipment including the 
> AN/URC-32 that I worked on in the USN.
> 
> At Ep of 1500 in AB1 3rd/5th is -30/35. However at
> 2000V it slips to -23/27. 
> This is a 2 tone measurement which disagrees with
> Toms claim of Eimac using 
> a single tone. Maybe they swing both ways (;
> In any case the -23/27 is what Ive experienced with
> that tube at 2KV in a 2M 
> amp before building the 3CX1000A7 and the generic
> 250 is a bit worse. This 
> was in the dark days and I used VR tubes for screen
> regulation. However in 
> this crowded area my 600W often got wide reports
> even tho the CE-100V TX was 
> rated at -30 ( A pair of 6550's that the audiopiles
> drool over)and the 6360 
> transverter output couldnt be that bad?? Those
> reports partially prompted 
> ( and another 3+ dB) the 3CX1000A7 with a rebiased
> brick in between the xvtr 
> and amp. The old xvtr was replaced about 15 years
> ago by a MM unit from your 
> side of the pond that I improved the RX a bit.
> 
> The RCA 8122 was about 3dB better in AB2 at 2500V
> and another 3 dB better 
> with Ians regulators. A pair of 8122's is in the
> NCL-2000 which I converted 
> to 6M in 1964 while I worked at National on the
> development of that amp and 
> still use today.
> 
> Ive also upgraded a few 6N2 Viking Thunderbolt amps
> with Ians kits so I do 
> have more than a passing aquaintance with tetrodes.
> 
> Carl
> KM1H
> 
> 
> 
> 
> 
> 
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