>Rich,
>
>Intermittent parasitics still seem unlikely from a classical'
>viewpoint..............yet I admit that you have a lot of evidence on
>your side!
I owe it to the folks who designed the 8877. They pointed me in the
right direction 11 years past. The rest I owe to curiosity, my
dipmeter, my handy-dandy 50x microscope, and a plethora of conversations
with amplifier users who had experienced the phenomenon. Honorable
mention goes to Messrs. Stewart and Rauch. Credit goes to the members of
QST's 1988 technical review group, and past QST Editor Paul L. Rinaldo.
>I figure there's a quote from Hamlet applicable...
>'There are more things in heaven and earth, Horatio, than are dreamt of
>your philosophy'
It seems to me, Peter, that there are not infrequently more things on
Earth to look at than meets our eyes.
- During the grate parasitics debate on the Internet, when I was
doggedly trying to get Mr. Rauch to tell me whether or not he used a VHF
suppressor in the design of the MFJ/AMERITRON 8877 amplifier, I received
a telephone call from an electronics engineer who was following the
debate. At work, he used a computer application to ascertain amplifier
stability, gain, linearity, on and on. He entered the parameters for an
8877 operating at 14MHz, with an anode-resonant circuit that had a
relatively high VHF Q . The computer app. indicated that the model 8877
amplifier was capable of oscillation between roughly 100MHz and 300MHz. .
I suspect that 3-500Zs can become marginally stable above 85MHz. The
next time you are inside a 3-500Z amplifier, Peter, it might be fun to
apply a dipmeter to one of the grid grounding leads. The next time you
are inside a 8877 amplifier, it might be interesting to apply a dipmeter
to one of the contacts on the grid-grounding collet. . . . Where did
we go wrong? -- by ignoring the presumably-insignificant
anode-to-cathode feedback capacitance, and by ignoring grid-resonance. .
. Alas, Murphy was right.
>(or, rather, in mine)
>
>Being rather philosophical after having a head on collision with a bus
>on my way to work yesterday morning - in my new car bought in August,
>and with only 1363 miles on it.
The great American philosopher 'Forrest Gump' said "Shit happens."
Indeed. It happens to 8877s and 8874s. I have a box of decapitated
8877s and 8874s, most of whose innards are littered with a miniature sea
of microscopic gold melt-balls. . . The good news is that scrap
copper goes for 75 cents per pound.
cheers
Rich--
R. L. Measures, 805-386-3734, AG6K
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