Good points Dick.
The 4CX250R/7580W and 8930 can push the IMD into the high 20's and then add
another 5-6dB using G3SEK's tetrode boards. Add NFB and you are at -40dB
3rd. Ive measured -35dB from my 6M NCL-2000 (8122's) without any NFB.
The 4CX350A and Svetlana 4CX400A are comparable and the 4CX350FJ is the best
if you dont mind a 26.5V filament, it will do -40 out of the box without any
The bogus 4CX800A is a dog that is run way over its true GI-73B ratings and
needs about 75-80% of the total Ip idle current to reach decent linearity
the way they are run in commercial ham amps. No wonder they burn up.
----- Original Message -----
From: "Dick Hanson" <email@example.com>
Sent: Saturday, May 22, 2010 5:38 PM
Subject: [Amps] 4CX250B Ratings in Dentron Clipperton V
> All these points are well and good about screen peaks, within the limits
> the screen dissipation etc.
> Heck, we could even add a grid current meter to make things really
> interesting, and pray never to see it move (much).
> If this discussion was about a 4CX350, 600J/JB, 800A, 1000A, or 1500B,
> be winding up with a pretty well-tuned amp, AND capable of some pretty
> decent 3rd and 5th order distortion products.
> 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
> than AB anything).
> If someone knows some tricks for adding 10db or so of distortion
> improvement, well then, now we're on to something.
> Otherwise, a 350A or re-socketing to a 800A would be a better choice.
> IMHO, 73
> Dick, K5AND
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