> >That means you only need about 300pF blocking C for 160
> >meters, if the anode system's operating impedance is 3000 ohms.
> >
> >I remember laughing at a friend of mine who stuck a 100pF
> >blocking capacitor (by mistake) in his 3-500Z amplifier for 160.
> >When he changed the part to 1000pF, nothing happened except
> >the tuning capacitor slightly changed position. Efficiency and power
> >out remained the same.
> >
> // Amen, Mr. Rauch, Another Ham radio old wives' tale bites the dust.
Industrial RF generators (Henry, RF Power Products, et al) operating on
13.56 mhz at powers from 1 to 5 kw all have something in common. They
use 200-400 pf blocking caps. I was "brainwashed" at an early age to believe
that 2000-5000 pf was needed on 160 meters because all of the amateur products
used that value in the "old days."
To answer the original question, I would say that the values for all tank
components
vary with the choice of tubes/transistors, the box chosen to house them, and the
layout. More experimentation, measurement, and trial-and-error is involved in
the
design stage than relying on a formula, or what someone else used in the past.
My guess is that the main cause of failure in a blocking cap is over-heating due
to
exceeding its RF current rating.
(((73)))
Phil, K5PC
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