[AMPS] FAILURE OF PARASITIC RESISTORS IN AL-811X AMPLIFIER

[Tom Rauch]

> > Any current transient in the anode's VHF-resonant circuit, produces
> > damped-wave ringing.  I have heard dozens of reports where a big-bang
> > was heard when the ZSAC switched on or switched off -- with no RF being
> > applied. 
> 
> It's not necessarily any ringing transient.  VCOs (real oscillators) are
> not started from a transient but basically oscillate due to the thermal
> noise of the transistors starting things off.  Same thing with an amp.  If
> the gain and phase margins are wrong, the thermal noise can start things
> rolling and from there it just goes and goes.

Hi Jon,

I've never seen an oscillator that required a hand crank, like an old 
model T Ford, to get it started.

I see very few oscillators that come with a hammer so you can 
"bang" them to get them started.

As you state above, if the regeneration is enough to have an 
oscillation...it is enough to start the oscillation.

As a challenge, try to design a conventional amplifier that can sit 
for weeks or months behaving only as an amplifier, but will 
suddenly switch into a saturated oscillation state when "tickled" 
with a transcient. Add all the feedback and resonat circuits you like.

It's amazing that we can't design a system like that intentionally, 
yet we are supposed to believe they occur everywhere by accident 
just because we want one simple universal cure for every amplifier 
and tube problem in the world!

Did your xxxxx fail? Must have been a parasitic! Fix it this way, 
because my way is the only way.


  


73, Tom W8JI
w8ji@contesting.com

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