[Amps] About single 4CX250b output power

[rlm]

On Wednesday, October 29, 2003, at 01:00  PM, Mike Tubby wrote:

>
> ----- Original Message -----
> From: "GGLL" <nagato at arnet.com.ar>
> To: "Amplificadores Lineales" <amps at contesting.com>
> Sent: Sunday, October 26, 2003 1:34 PM
> Subject: [Amps] About single 4CX250b output power
>
>
>>     Hello to the list, I want to know if is it possible to obtain 350
>> watts output from 160 to 10 with a single 4CX250b tube, for linear
>> amplifier service, and which working class? AB1, AB2?; 2000 Plate 
>> volts
>> maximum is needed?.
>>
>> Best reagrds
>> Guillermo - LU8EYW.
>>
>>
>
> Page 65 of Eimac's "Care and feeding of power grid tubes" shows a
> selection guide for SSB service for which the 4CX250B is listed as 
> being
> capable of 348W "useful power output" in AB1 with a 3rd order 
> distortion
> product of -25dB (doesn't say whether its relative to carrier power or 
> one
> tone of two tones).
>
> I suspect that this is in "ideal conditions", new tube, perfect 
> matching on
> input and output, correct anode and screen voltage, etc. etc. YMMV.
>

Eimac measures IMD relative to two tones, so the IMD relative to PEP is 
31db-down instead of 25db-down.  However, I found that with 2400vdc on 
the anodes of 4cx250s, and loading for a minimal amount of screen 
current, the IMD products were no worse with the amp on than with the 
transceiver alone.  The reason for this is that most of the distortion 
is produced at lower anode voltages,  Thus, for SSB only, raising the 
anode supply V, and minimizing screen I helps to minimize anode V 
incursion into the distortion zone.  //  Another way to minimize IMD is 
to select a tube with more peak emission.  Eimac puts a "J" suffix on 
such devices. Since there is no such thing as a free lunch, more peak 
emission means more filament power is consumed.  Typically, this is c. 
35% more than for the normal version of the tube.  Naturally, the 
characteristic curves of J-version tubes are much flatter at the 
low-end than the garden variety version.  For example, the J version of 
the 4cx10000D has an IMD of c. 47db-down below PEP, or far better than 
any transceiver made today, but it has a 104A filament instead of a 75A 
filament.

cheerz



> Mike G8TIC
>
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Rich Measures, AG6K, 805.386.3734.  www.somis.org/