Hi Rodger
Physically the tubes are not the same. The (Eimac)CPX version has a taller
ceramic portion allowing a much higher plate voltage, (3500 volts).
Svetlana made this tube with the taller ceramic insulator for both the CPX
and CX versions. Running the higher plate voltage allows for lower drive
requirements. K1FO has done extensive work with these tubes over the years.
His findings can be found here,
http://home.cshore.com/lunarlink/opentechical.html
73
Paul
PAUL HEWITT
WD7S PRODUCTIONS
QRO HOMEBREW COMPONENTS
http://home.earthlink.net/~wd7s
----- Original Message -----
From: "Roger" <sub1@rogerhalstead.com>
Cc: <amps@contesting.com>
Sent: Thursday, December 25, 2008 10:59 AM
Subject: Re: [Amps] 3CPX800A7
>
> They are basically the same tube except the "P" has more cathode
> emission capability (IIRC).
> They are physically the same so there is no more "head room" than with
> the regular 3CX800. IOW used in a given duty cycle such as RTTY they
> perform the same. With pulse the "P" version can run a higher peak
> power. Used in a commercial amp you should see no difference without
> driving it harder which would probably require more air.
>
> All in all they are a good replacement if available at reasonable
> prices. For more power, as I said it takes more drive and more cooling.
> The amount of extra power gained in that fashion is not all that great.
> You do see "export versions" of some amps using 3, 3CX800's and that is
> noticable, but for a couple thousand dollars you are still only gaining
> about 50% of two tubes, or less than 2 db.
>
> Having said all that, (IIRC) Henry used to make a version of the 6-meter
> amp that used to 3CPX800 to run the legal limit on CW and SSB.
>
> 73
>
> Roger (K8RI)
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