Now here is an example of a tube operating at max output with out regard to IMD
products. I expect this spec. was intended for mobile or portable military
radios where power and compactness is more important than splatter. Look at the
Class B operation of the 4-65A at 325 watts PEP output. A note recommends
adjusting the control grid bias for ZERO plate current.
From: email@example.com [firstname.lastname@example.org] On Behalf Of
jonathan white [email@example.com]
Sent: Sunday, May 23, 2010 7:05 AM
Subject: Re: [Amps] 4CX250B Ratings in Dentron Clipperton V
On 23/05/10 09:10, Ian White GM3SEK wrote:
> Dick Hanson wrote:
>> Unfortunately, however, we're sort applying lipstick to a pig here. The
>> 250B is just not a very 'worthy' tube at -22db; hard to gain BFF among
>> your neighboring six meter guys..... Might as well run an old model
>> brick with no active bias (closer to class C than AB anything).
> At output levels of about 250W PEP per tube, the 4CX250B is capable of
> IMD3 figures around -35dB (referenced to PEP).
> It is Eimac's marketing claims, inciting users to drive the tubes to a
> much higher power output, that were "unworthy"... not the tube itself.
I agree with you Ian, 25yrs back,there was some outrageous signals on
2mtrs with overdriven `250b`s poor regulation of screen supply, poor
anode supply and zenner diode stacks feeding screen.
Also the QQVO6-40a was another valve that suffered that treatment.A
German outfit was making single valve QQVO6-40a with 100w PEP out,and a
`4CX350b at approaching 500w .A local station 2miles was producing
splatter across most of the band and that was with the antennas
disconnected and I never used a masthead preamp.
I think this is were Mr Nelson stepped in.
PS I used a 6-40a driven to 40w PEP, into a Cushcraft Boomer, the WMD of
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