> Try and have it your way as usual. Ive seen plenty of
> plate blocking caps heat up and change the output tuning
> and still not be at the point of failure.
You really ought to send the capacitor that drifts and
doesn't burn up to a science museum!!!
Let's assume the tube loadline is 3000 ohms and see if that
claim makes any sense at all:
A 1000 pF cap 44 ohms non-dissipative reactance on 80 meters
A change from 1000pF to 100 pF would change the SWR seen at
the tube on 80 meters by the following:
3000 ohm tube loadline
1000pF blocking
209.2 pF tuning cap
10.3uH tank coil
1375pF load cap
tube sees SWR of 1.01
Now lets make that capacitor drift to 100pF
3000 ohm tube loadline
100 pF blocking
209.2 pF tuning
10.3uH tank coil
1375 pF load
tube now sees a roaring bad 1.136 : 1 SWR. Hardly a change
So how far do we have to retune that capacitor that drifted
from 1000 pF down to 100 pF???
3000 ohm tube loadline
100 pF blocking
207.2 pF tuning
10.3uH tank
1375 pF load
tube is back to a comfortable 1.01 SWR
The net change in tuning cap value to compensate for a
change from 1000 pF blocking to 100pF blocking is 2 pF.
If we have a blocking cap that drifts so bad it requires
retuning the tank, it is a record holder.
People get way too stressed out with the value of blocking
caps. Unless the thing is cracking, arcing or smoking it has
little effect on anything from efficiency to power output to
tuning.
73 Tom
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