"True, however, prayer cloths are not all that reliable. The main
reason for going after a parasite in the anode circuit is that it's
where the damped wave VHF ringing takes place - whenever anode
current changes - that starts the snowball rolling downhill."
It is also possible that a parasitic suppressor is an admission of sloppy
design work. There are many amplifiers built using the 8877 tube with no
parasitic suppressors. Can you imagine installing a parasitic suppressor
into uhf cavity? Perhaps you can make the entire cavity out of nichrome.
When designing an all band hf amplifier, it is probably easier to throw in a
parasitic suppressor for the assumed
natural frequency of oscillation in the existing structure than to use a
network analyzer and a lot of effort to reduce the oscillations to a point
where they no longer will occur.
Rich talks about prayer cloths - but in fact his nichrome suppressor is
acting as a prayer cloth. This is a case of putting that in will make sure
something bad will not happen. It takes confidence in ones ability to build
an amplifier without one - because they you are relying on your skill as a
designer and builder - and expertise in measuring.
I have built amplifiers with and without parasitic suppressors and have had
parasitics in both - but then again, I am only an amateur.
73, Colin K7FM
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