[Amps] AL-80B questions

[Michael Tope]

> Don was pretty insistent about installing the AG6K Low VHF-Q supressor kit
>based on the numerous articles written and also based on other amateur's
>reported success with the kit.  He also told me tonight that he knows a guy
in >Wyoming with an older AL-80 who apparently had similar problems 'till he
installed >a different supressor.  We did not install any of the other items
in the kit yet.  I left >him with a semi-worn Eimac bottle to use 'till his
replacement arrives.
>

As I see it, the one problem with relying on tube failure as
evidence of the efficacy of parasitic suppressors, is that
there may be no way of knowing if the new suppressors are
the cure or just coincident with the installation of a new good
set of tubes. In other words, if someone has a string of tube
filters and then plugs in a set of nichrome suppressors and
the failures stop, it doesn't mean that the suppressors are the
key ingredient in the cure. It's also possible that the failures
stop because the new tube(s) installed with the new suppessors
are from a different manufacturing lot or just don't have the
same inherent defect as the previous tube(s). To control the
experiment, you would have to run the amp for a while with the
new tube and nichrome suppressor to satisfy yourself that the
tube was through infant mortality, and then switch back to the
old suppressors to see if a failure ensued. Even then, you don't
have 100% proof that the suppressor was the cure. In any
case, the aformentioned scenario could explain why there is
a body of anecdotal evidence that the nichrome suppressors
have provided a cure for high failure rate amplifiers when in
fact the suppressor had nothing to do with the failure. Of course
in the few case I have seen cited where the improved stability is
directly observed (smoother tuning, no signs of oscillation), this
pitfall doesn't come into play (I seem to recall that VK6APK
recently cited a case where the nichrome suppressors helped
stabilize a squirrely homebrew amplifier, but again this amp
exhibited poor tuning and tendency towards non-catostrophic
parasitic oscillation - e.g. no tube failure was involved).

73 de Mike, W4EF................................................