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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 20:07:33 -0400
List-post: <">>
I dont know of any commercial SSB application; that doesnt mean there wasnt 
any. They were popular in FM mobile service until the 5894 came out.The CAA 
used them on AM around 140mc in the late 40's.  Never cared for them, need 
too much voltage for too little power.

Eimac keeps insisting that Class B can run idle current which technically is 
correct.....just barely


----- Original Message ----- 
From: "Fuqua, Bill L" <>
To: <>
Sent: Sunday, May 23, 2010 6:16 PM
Subject: Re: [Amps] 4CX250B Ratings in Dentron Clipperton V

> Your are right. I need to put my glasses on next time. However, I believe 
> in this case the target is getting max output with out much regard to IMD.
> Another bit of confusion, 50 watts idle dissipation in a 65 watt plate 
> dissipation tube sounds far from class B operation. Should be AB2.
> These were used in the PRC47 transceivers but only at around 100 watts 
> output. I wonder where they were used for 300 watts output SSB suppressed 
> carrier?
> 73
> Bill wa4lav
> ________________________________________
> From: Carl []
> Sent: Sunday, May 23, 2010 3:52 PM
> To: Fuqua, Bill L;
> Subject: Re: [Amps] 4CX250B Ratings in Dentron Clipperton V
> And if you read further it also says for SSSC to adjust the bias for 50W
> plate dissipation.
> Carl
> KM1H
>> 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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