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Re: [Amps] About single 4CX250b output power

To: "Mike Tubby" <mike.tubby@thorcom.co.uk>,AMPS <amps@contesting.com>
Subject: Re: [Amps] About single 4CX250b output power
From: rlm < <r@somis.org>>
Date: Thu, 30 Oct 2003 04:33:29 -0800
List-post: <mailto:amps@contesting.com>

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



----- Original Message ----- From: "GGLL" <nagato@arnet.com.ar> To: "Amplificadores Lineales" <amps@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/

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