In the 1960s I knew a guy , John Brown, who tried a number of tube
types in grounded grid.
The most spectacular was 4ea 4-65A's with a series control grid resistor
to limit its current. These would almost get white hot
at max output. He tried 4CX250Bs with a series resistor ( they were fried
with out the resistors) and did sort of work but
he gave up on it. I don't know if the signal reports were bad or if there
was some other problem. But have not seen any others
try it since until you posted this article.
This 1200 watts out with a pair of 4cx250B's sounds a bit high. Most
likely 4 tubes.
If you think about it the peak plate current should be the same with a
4cx250B in class AB1, control grid at zero and
screen at 250volts say, and in G-G, g1 connected to K ,configuration where
the cathode to grid voltage is zero and peak
cathode voltage -250 volts. Power out per tube should be 300 or so watts
plus drive power.
To get 1200 watts with two tubes you would need much more plate
voltage and drive voltage.
73
Bill wa4lav
At 07:56 AM 10/13/2010 -0400, Hsu wrote:
>Another example, 73 magazine March 1973 P50-54
> "The ample amplifier".a pair 4CX250B in G-G configation, the control
> grid contact to cathode and the screen grid to ground.
> the builder point out that the power gain is 6( 200W in 1200W pep
> out), I have no this article, if anyone would like share with me, I'm
> very glad.
> 73!Hsu
>
>----- Original Message -----
>From: "Hsu" <hsu4qro@gmail.com>
>Cc: <amps@contesting.com>
>Sent: Wednesday, October 13, 2010 7:35 PM
>Subject: cathode driven 4CX250B and super cathode driven
>
>
> > Please view http://home.comcast.net/~k7rld/4cx250bamplifier.htm, Anyone
> have built it?This amp's sch have been modified, in
> origional schematic, the R1 and R2 contac with cathode, but this
> contact to ground.
> > I have modified my Henry Tempo2001 to a pair 4CX250B as original
> schematic in end of 2008, but I found the power gain is too less, so I
> give it up.
> > I use simlar 30s1's configation, now, it works great.
> > 73! Hsu
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