The 4CX250B is a 250 watt ceramic tube based upon the older 4X150 design. It
was not designed for grounded grid service. Like the 4CX1000, the grid is
fragile.
In the 4-1000, the grid is so stout that you can simply connect the grids
together and ground them. If you do that you will destroy the tube on the
first transmission. You can use cathode drive, but the grid and screen must be
at their normal value.
You can hang a low value resistor on the 4CX250B grid and drive the grid, but
the tube is not great on distortion so it should only be done if you have some
sort of feedback. Cathode drive has an advantage in that there is some
inherent feedback.
With the supply of Russian tubes available for grounded grid, there is not a
good reason to use the 4CX250B tube in a high power low band amplifier - except
for the ham that has either no funds or no source of other parts. They are
still useful, however, as an amp for a low power transmitter (like 5 watts).
They used to be useful on vhf, because they work fairly well at vhf and low uhf
- but the newer Russian tubes have much more dissipation that it hardly makes
sense to make a high power amp using these old relics.
Colin K7FM
-----Original Message-----
>From: "carl s." <carlseye@tampabay.rr.com>
>Sent: Apr 3, 2006 1:20 PM
>To: Amps@contesting.com
>Subject: [Amps] tubes
>
> Who can tell me about the 4CX250B tube.???
> power ? GG. capabilities, Etc.:: (hf only )
> just want to know !!!!!
> carl / kz5ca
>
>_______________________________________________
>Amps mailing list
>Amps@contesting.com
>http://lists.contesting.com/mailman/listinfo/amps
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|