[AMRadio] Class C finals


John Coleman ARS WA5BXO wa5bxo2006 at pctechref.com
Tue Nov 14 00:40:56 EST 2006


	The Drive on a class C circuit is set to swing the conduction of the
tube from cutoff to saturation with in a RF cycle.  In this type of service,
the tube is cut off for about 290 degrees and at saturation for about 70
degrees of the input RF cycle.  I use the word "ABOUT" because obviously
there is some time that it is in transit and this is where the plate
dissipation is greatest.  Once the bias and grid current have been achieved
by the grid leak due to the drive then increasing the drive has very little
effect on the output.  Decreasing the drive below the point where output
begins to drop will result in the service not being class C any longer.
That is to say that the ratios of conduction angle for saturation and cutoff
are no longer proper for the class of service and efficiency will suffer.
I'm sure since the 2E26 does not have the space charge that the 6146 has,
then it is designed to run at lower bias voltage and RF drive.  Whether you
run it a 2ma or 3ma will have very little effect on the output or the
efficiency.  If you're going to pull the loading back to draw less plate
current (a function of the tank loading circuit) when the plate tuning is
dipped, then that could be done with either tube.

John, WA5BXO   

-----Original Message-----
From: amradio-bounces at mailman.qth.net
[mailto:amradio-bounces at mailman.qth.net] On Behalf Of Jack Schmidling
Sent: Monday, November 13, 2006 10:38 PM
To: Discussion of AM Radio in the Amateur Service
Subject: Re: [AMRadio] Class C finals

John Coleman ARS WA5BXO wrote:

> 	So it would seem that if you replace the 6146 with a 2E26 then in
> order to get the proper operating parameter for the 2E26 one would need to
> reduce the loading.  So why not just reduce the loading on the 6146?

The suggestion was to reduce the drive on the 2E26 and load it to where 
it is comfortable which suposedly would be at 15w.

js




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