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Re: [Amps] 4CX250B Ratings in Dentron Clipperton V

To: "Fuqua, Bill L" <>, <>
Subject: Re: [Amps] 4CX250B Ratings in Dentron Clipperton V
From: "Carl" <>
Date: Sun, 23 May 2010 15:52:53 -0400
List-post: <">>
And if you read further it also says for SSSC to adjust the bias for 50W 
plate dissipation.


> 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.
> 73
> Bill wa4lav
> ________________________________________
> From: [] On Behalf 
> Of jonathan white []
> Sent: Sunday, May 23, 2010 7:05 AM
> To:
> 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
> the day!
> Regards
> Jon G8CCL
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