[Amps] HF amp output power dropping

[Tom Rauch]

> It could very well be the plate blocking cap, especially 
> if it is undersized for that power or not even rated for 
> RF use such as the TV doorknobs.


Not much chance of that. It is  a self-testing component.

If the plate blocking cap is dissipating hundreds of watts 
it would explode or go up in flames in a matter of seconds.

It is not value critical, there is barely a difference in 
output tuning when values as low as a few hundred pF are 
used on 160 meters in amps with a reasonably high operating 
impedance, let alone on high bands.

If we just take a few moments to actually look at the 
impedance change at the anode as the blocking cap is 
changed, we see how unimportant the value really is in 
operation.

I remember when a buddy and myself were visiting K8KAS and 
he had a 100 pF blocking cap in his 160 monoband amp. We 
laughed and poked fun at him for something so silly. He got 
all red-faced and said he misread the part value.

When he replaced it with a 1000pF cap the tuning barely 
changed, the loading didn't change at all, and the amp ran 
exactly the same power. I went back home and looked at the 
impedance change at the anode and learned my lesson.

73 Tom