>
>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.
No one has said that all big bangs have one root cause. Your position
appears to be that intermittent VHF parasitic oscillations can not cause
big bangs.
>
>> 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.
>
[chortle]
>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.
Do photons from the depths of outer space cause sudden conduction by
striking atoms in geiger tube?
>
>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
who could be looking at a meter at the instant of a big bang?
> will heat the gold enough to ruin the plating.
Not quite. The plating is not ruint, per se. The errant gold causes
anode/grid arcs and cathode grid arcs which can cause the cathode coating
flake off.
Because of skin effect, only the top layers of gold atoms are heated
enough to boil off.
>
>3.) (The latest one here) A VHF parasitic will destroy the inside of a
>resistor, and not the outside layer of the element,
There is no outer layer to the carbon-comp element.
>with heat damage while lower frequencies mainly destroy the outside.
>
The bubbles that form on the phenolic case do not destroy anything.
>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.
''Helices'' is plural. ''Helix'' is singular.
>
>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.
>
True enough. What you fail to mention is that
Tune-Caps have internal resonances at VHF. As I recall, you discovered a
Tune-cap resonance in the AL-80 that was around 170MHz. It sorta looks
like you are dodging this matter, Tom.
>6.) A healthy tube that won't arc at HF in normal operation will
>suddenly arc at VHF from a spurious signal.
>
You are the only guy I know who says that an arc in a vacuum can make a
big bang in the outside world.
>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.
Parasites are not the cause of all damage in amplifiers. It is my
opinion that they are one cause of damage. After my second article on
parasites appeared in *QST*, I began receiving lots of letters from
amplifier owners. The one day record was 33 letters.
Could that many hams be fooled by snake oil?.
-- Mr. Rauch: Would you like to receive a photocopy of Mr. G. W.
Fyler's article about parasitic oscillations that appeared in the 1935
IRE Journal?
>
>
>
cheers, Tom.
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