The 4CX1500B is not a tube suited for use in a grounded grid configuration.
It works very successfully in the grid driven mode if you use a passive grid
input, ground the screen, and float the screen and bias supplies below
ground. There are a number of examples of this arrangement available.
> -----Original Message-----
> From: firstname.lastname@example.org [mailto:email@example.com]On
> Behalf Of Felipe Ceglia - PY1NB
> Sent: Monday, August 27, 2007 4:10 AM
> To: Amps@contesting.com
> Subject: [Amps] 4cx1500b amp conversion
> Hello fellows,
> I am finishing the process of converting an JRC NAF-521 HF amplifier,
> which originally came with a pair of 8122 to use a 4cx1500b tube.
> It seems like it is self-oscilating on VHF frequencies as the anti
> parasitic choke got hot, and the resistors even got unsoldered with heat.
> It is in grid driven configuration, and I am wondering about putting it
> to a grounded-grid configuration, but in other hand I would not feel
> very good about it, as I already have in hands a nice power supply to
> run it from.
> You may see the tube part of its diagram and rf deck photos at:
> Would you suggest anything, another configuration?
> 73 and thank you,
> Felipe - PY1NB
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