On Aug 26, 2006, at 12:00 PM, Harold Mandel wrote:
> Gentlemen,
>
> A previous post mentions a phenomenon wherein is written
> "parasitic oscillation" and what I deduce as filament sag.
>
> Is it possible that these two conditions are related?
>
> It is understood how a strong magnetic field within the tube envelope
> can perhaps alter the filament geometry, but can this happen as a
> result
> of a VHF "excursion?"
Hal -- Parasitic suppressor resistors are normally paralleled by 60
to 100nH of L. Thus, to develop enough V across a suppressor to
damage the resistor, VHF is required. After observing a number of
cases in SB-220s and TL-922s where a large increase in VHF suppressor
resistance accompanied a blown grid RFC, I concluded that VHF energy
was the common denominator.
RE" Sag: In cases where a grid-filament short occurs in a
3-500Z during an intermittent parasitic oscillation, the filament
does not sag, rather it is pushed sideways toward the grid--
presumably by EMF from the large flow of grid current during the
parasitic. The amount of this current is anybody's guess, but it's
enough to do damage
>
> Respectfully,
>
> Hal Mandel
> W4HBM
>
>
> [SNIP]
>> Hundreds of empirical observations from all makes of amplifiers
>> must be
>> wrong. Clearly, the problems must be the mysterious parasitic
>> oscillation, which obviously is pushing the filament sideways.
> [SNIP]
>
>
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>
R L MEASURES, AG6K. 805-386-3734
r@somis.org
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