[AMPS] Poor science

[Tom Rauch]

on about how oscillators work, someone said:
> 
> > If the amplifier is going to oscillate, it will oscillate.  It won't sit
> > there and just do nothing for weeks, months, years, etc. and then
> > suddenly WHAMMO!
> 
> This is a misrepresentation, and I think you know it. The amp is in use,
> and drive, impedances, etc are changing from time to time. It's not just
> sitting there. The spurious oscillation hypothesis is that particular
> combinations of drive, impedance, etc. are deadly.

I don't see anything wrong with the first statement.

The idea an amplifier with enough feedback to be an uncontrolled 
oscillator would sit there stable for months or years and the 
suddenly burst into an oscillation that has so much self-sustained 
feedback that causes an explosion is based on a ridiculous effort 
to make any failure look like it had one root cause.

> You then go on to say:
> 
> > Too true.  Too bad some people don't understand the laws of physics.
> 
> There is no law of physics that forbids the behavior described.
> 
> I'm a physicist; I would know.

Then you better read Richard Measures claims.

1.) A photon from space can strike a cathode and start a current 
avalanche that will arc the standby relay contact over and the tube 
will break into a wild parasitic oscillation and cause a high voltage 
arc.

2.) A gold-coated control grid can take an almost unlimited amount 
of grid current without failure, but a sudden  VHF oscillation that 
won't even show on the meters will heat the gold enough to ruin the 
plating.

3.) (The latest one here) A VHF parasitic will destroy the inside of a 
resistor, and not the outside layer of the element, with heat 
damage while lower frequencies mainly destroy the outside.

4.) A tube that can only emit so many electrons can, from a 
parasitic, suddenly bend a filament helice but it CAN'T do the same 
from other causes.

5.) The voltage developed across a few ohms of reactance (the 
plate tuning cap at VHF) can get so high when driven by a tube 
(see the current limitations mentioned in 4) that the tank can arc 
components that won't arc at HF.

6.) A healthy tube that won't arc at HF in normal operation will 
suddenly arc at VHF from a spurious signal. 

This whole parasitic thing is a major exercise in bad science and 
bad physics. I suspect it is designed to make a few bucks selling 
snake oil to suckers, or to woo a fan club of people who just don't 
quite understand how things work and are looking for one simple 
answer to complex questions.



73, Tom W8JI
w8ji@contesting.com

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