[Amps] Parasitics & Filament Sag

[Tom W8JI]

>    You raise a good point which could be extrapolated like 
> this: Parasitic
> oscillation MAY be the cause for SOME grid-to-filament 
> shorts. There has
> been equal number of situations where the application of 
> Rich's nichrome
> wire suppressors eliminated the problem as well as not.

In random tests when an unknown intermittent problem occurs, 
no change at all can result in what people perceive as a 
cure.
This why double blind tests are done.

The random coincidence effect is why the new age medicines 
and the old copper bracelets for arthritis have a following 
that will argue to the death about the wonderful cures, and 
why numerology and astrology have followers.

For example if I had an amplifier with a tube that randomly 
failed twice, and I changed the suppressor and the tube, I'd 
have no idea at all if it was blind luck or the suppressor.

If I had a problem with an intermittent arc and I took 
everything apart and cleaned it up as well as adding 
nichrome, I'd have no idea if dismantling and perturbing 
several things fixed the problem or the nichrome did.

What CAN be proven beyond a doubt is nichrome makes very 
little difference at VHF over a simple turns or resistance 
adjustment in a conventional suppressor.  The VHF 
performance is essentially the same. The greatest difference 
is at HF and lower, not at VHF. This is easy to prove, and 
100% repeatable.

N7WS made independent measurements of this.

I measured the Q of a nichrome kit for 3CX800's, and the 
actual VHF Q increased with the nichrome over the stock 
suppressor. That was because the nichrome was a hairpin and 
not a multi-turn coil like the conventional suppressor.

73 Tom