[Amps] Parasitic Oscillation

[Harold B. Mandel]

Will matney raised an issue we have hammered and hammered on this
reflector from Day One: Parasitic Oscillations~Phenomenon or
Hallucination?

Will is mindful of generations of amplifier builders incorporating a
suppression
network in their circuits. I've seen anode suppressors for over forty
years of
amateur radio and agree that there might be a reason to include them.

Looking to commercial manufacturers,  it seems that if something isn't
necessary it usually isn't included. One of my amplifiers came without
a High Voltage standby switch but did have anode suppressors.

My old SB-220 had suppressors. Would Heathkit have included them
if they thought they could get by without them?

AG6K invested years of his life and probably a courtly sum of money
destroying equipment intentionally to discover attributes of how and why
suppressors work. This led to the amendment of suppressor design so
that output-Q would be drastically reduced at VHF events where 
unprotected devices would be easily destroyed. Mr. Measures came up with
a system of suppression that seems to protect expensive components
in a number of ways, but there's no such thing as a free lunch.

In building tube amplifiers for HF service I ask myself what am I wanting
out of life: Performance, Reliability, Bang-For-Buck?  Am I willing to
trade
a bit of performance for something else, like safety and reliability,
perhaps?

There's $4,000 worth of tubes around here and I really don't feel like
buying new
ones because an event caused a runaway oscillation. While my antenna
tuning 
apparatus is supposedly secure there's always the chance that something
happens to the 
600-odd-foot antenna wire out there, right while I'm in the middle of an
RTTY
transmission. I would much rather buy a handful of small parts and spend
a weekend
soldering them together than PayPal-ing C&D or someone similar thousands
of dollars
for another tube. 

Even if Parasitic Oscillations are humbuggery, the cost of inclusion is
but a fraction
of the worth of an amplifier output device. 

Lastly, none of my amplifiers have ever gone into self-oscillation except
a particular
Australian tetrode GU-78B, and that machine didn't have an AG6K
suppressor,
nor did it have a neutralization circuit. That amp was the only one out
of the eleven
seeing service here.

Respectfully,
Hal Mandel
W4HBM