[AMRadio] 4-1000A Grounded Grid Class-C


Steve WA1QIX wa1qix at piesky.com
Thu Oct 3 10:22:03 EDT 2013


At 07:55 PM 10/2/2013 -0700, you wrote:

>Is it possible to run a 4-1000A in grounded gridS, cathode driven, biased 
>for class-C and then plate modulate it and get 100% modulation? Has 
>anybody tried this?

It is possible.  The only important factor is how does the unmodulated feed 
through power effect the linearity of the RF amplifier as a square law device.

As the modulation approaches 100% negative, the feed through power becomes 
an increasing factor.  It will not behave like a classic negative peak 
limiter, which has no effect until it comes into conduction.  So, there may 
be some distortion, but how much is unknown having never actually done it.

Do you know how much feed through power you actually get?  This will be an 
important number to know.  Because AM is a square law function, 1/10th the 
unmodulated plate voltage (90% negative modulation) is 1/100th the 
power.  If you have, say, 5% feed through power, that is actually a lot 
with respect to 100% negative modulation.  I didn't figure it out, but it 
may be 20% modulation... just something to consider.

If you do this arrangement, don't use the feed through as a negative peak 
limiter (of sorts) without also protecting the modulation transformer (if 
there is one).  Implement a protection diode/resistor/power supply across 
the transformer secondary to protect the transformer during the periods of 
the modulation cycle where there is no current.

If it were me, I'd give it a try !! :-)

Regards,

Steve



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