Eimac short form catalog gives typical operation in AB1 as 300W o/p with
2000Va and 400Vg2. Seems to me (and I have used a lot of 4CX250 types)
that 600W from a pair is all you can really expect and maintain linearity.
Of course if linear operation is not required - eg for CW - then the tubes
can be driven harder, more towards Class C, and then you can expect a
little more out. But the maximum grid dissipation is only 2 Watts so that
could be a bit risky!
John ZS5JF
----------
> From: Rich Measures <measures@vc.net>
> To: Ian White, G3SEK <G3SEK@ifwtech.demon.co.uk>; amps@contesting.com
> Subject: Re: [AMPS] tuning capacitor & insulator
To: <amps@contesting.com>
> Date: 18 December 1998 02:25
>
>
> >
> >Rich Measures wrote:
> >
> >>>and last ,i'm looking for a high power amp
> >>>for 2 meter ssb ( 500 + out put) any body
> >>>want to sell one?
> >>
> >>A pair of 4cx250Rs in parallel, self-contained, designed and built by
> >>yours truly. 20db gain. Class AB1. About 1000pep watts out on SSB.
> >>designed for10w pep drive. The built in 2200v power supply is not
> >>suitable for FM, RTTY or A0. $100 plus ups. 120v/20a. Must be tuned
up
> >>with a keyer sending 50wpm dits, or with a tuning pulser.
> >
> >The gain is right - and by goodness the price is certainly right -
> >but expect no more than 500W PEP of *linear* SSB. Otherwise expect to
> >lose a lot of friends.
> >
> ? The 7580/4CX250Rs have 400v on the screens. According to Eimac's
> curves, c.1.3 peak amperes of anode current flows when the grid potential
> is 0V and the screen potential is 400V. The 1.3a constant-current curve
> appears to be reasonably linear up to 0V on the grid. By my calculation,
> the pep input is around 1850w.
>
> >No criticism of Rich's particular design; the limitation is in the tubes
> >themselves.
> >
> ? Did you perhaps presume that the 7580 has the same power capability as
> a 4CX250B?
> >
> - later, Ian
>
>
> Rich...
>
> R. L. Measures, 805-386-3734, AG6K, www.vcnet.com/measures
>
>
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