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[Amps] 4CX250B Ratings in Dentron Clipperton V

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Subject: [Amps] 4CX250B Ratings in Dentron Clipperton V
From: "Jim Brown" <>
Date: Fri, 21 May 2010 11:15:47 -0700
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I've just fired up a Dentron Clipperton V modified for 6M operation per 
Dentron instructions. It uses a single 4CX250B in Class AB2. The bias is 
adjustable, and the factory recommends 50mA plate current with no signal. It 
takes about 15W to give me 250W-300W out. 

My question is about power ratings. I want to use it on both CW and SSB. How 
hard can I push it without damaging the tube on SSB? The DC current rating is 
250mA. In SSB mode, I can get 200W indicated on a Bird with an indicated 
plate current of 200 mA or so (this is with modulation, not tune-up). I'm 
tuning up with high speed dits, so that I should be tuning for that peak 
power. Is this a reasonable way to run it, or am I pushing too hard? 

When I run CW,can I increase the envelope power on CW if I stay below 250mA 
average current (as indicated on the plate meter), or do I need to stay below 
250mA when I tune key-down?   Can I change the bias to get more than 250W 
out, or do I need to make other changes to the circuit to change the load Z?  


Jim K9YC

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