Re: [Amps] About single 4CX250b output power

[Bill Fuqua <wlfuqu00@uky.edu>]

One option would be to cathode drive it (if you have the drive power) with 
it operating in AB1 with usual bias.  This would provide feed-thru power 
and improve linearity due to inherent negative feedback in the cathode 
circuit. Since there is no grid current and very little screen current it 
should offer a very low distortion solution. The instantaneous plate 
current should be the same as the cathode current within a few ma. unlike 
zero bias triodes.  What really eats up these tubes is high filament 
voltage. They loose emission very quickly if you don't pay attention to the 
6.0 volt spec..
   Now I am wondering if tuned cathode is necessary as in triode g-g 
amplifiers. I would suspect the cathode impedance to be more consistent 
during the conductive part of the cycle since there is no grid current.

73
Bill wa4lav


At 10:36 AM 10/27/2003 +0000, Steve Thompson wrote:
> On Sunday 26 October 2003 13:34, GGLL wrote:
> >     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?.
> The STC datasheet gives typical 2 tone operating figures of -30dBc 3rd order
> and -50dBc 5th order at 325W pep, 2kV anode supply and 100mA quiescent..
>
> I reckon you do well to get that much output in practice. 275ish is a good
> limit if you want a nice clean amp.
>
> Steve
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