Samuel Hunt wrote:
Hi all.

I'm trying to find a good circuit for a Class C 4CX250B linear.

I've found a few for multiple valves in Class A, but I'm after just a simple
circuit that shows a 4CX250B linear for 2m with Class C biasing.

Idea is to use it for a little project where I want to run about 100W, but
run it cleanly without all the RF hash that transistor amps give.


Can anyone point me in the right direction?

Also, how would you go about varying the RF power output on a 4CX250B linear
in class C? Is it by varying the 1.2kV supply voltage, which would make
sense, or is there some other recommended way?


Sam


Oxymoron. Class C is NOT linear!
Now if you want to amplify CW or FM signals, class
C is fine. For AM or SSB signals you want class A, AB or B.
For this tube the grid #1 bias, grid #2 voltage and grid #1
drive (signal input) are different as you change class of
operation. (Mostly the screen and plate voltages can remain
the same and just change the resting plate current with the
bias and don't apply more than a specific signal level so
your max plate current isn't exceeded.)

Ken Scharf kirjoitti:




Oxymoron. Class C is NOT linear!

True
Now if you want to amplify CW or FM signals, class
C is fine. For AM or SSB signals you want class A, AB or B.
For this tube the grid #1 bias, grid #2 voltage and grid #1
drive (signal input) are different as you change class of
operation. (Mostly the screen and plate voltages can remain
the same and just change the resting plate current with the
bias and don't apply more than a specific signal level so
your max plate current isn't exceeded.)

Hi

Class C isn't fine.
Class C is producing a lot of harmonics
Specially odd ones are bad.
I don't recomment class C elsewhere but for transistor FM use in VHF and
UHF
Maybe also for KISS QRP in HF CW

73 , Risto OH2BT