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[AMPS] Blown TL922A... What to do?

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Subject: [AMPS] Blown TL922A... What to do?
From: W8JI@contesting.com (Tom Rauch)
Date: Sun, 10 Sep 2000 20:17:21 -0400
> My engineering background and professional experience are in digital
> design and software engineering, not RF design. Disentangling their
> technical arguments would take more effort than I care to spend. 

The arguments aren't all that tangled. 

My conclusions are based on my experience and 
measurements...and knowing what fails in the field as a percentage 
of what goes out based on feedback over the past twenty years  

My conclusions are all rooted in provable documented science, and 
not based on any personal issue.

> my amplifiers (AL1200, SB220, SB201) has ever flash-banged, so I'd rather
> spend what free time I have chasing DX or writing station automation
> software. But a competent RF engineer should have little difficulty,
> particularly with the tools available today:

That's true.  
 
>   1. select an appropriate circuit modeling program

Why model when you can measure?
 
>   2. construct a model of the tube in question, parametizing manufacturing
> variances

Why model when you can measure?
 
>   3. construct a model of an amplifier circuit in question, parametizing
> component tolerances

Why model when you can measure?
 
>   4. discover combinations of parameters, if any, under which VHF
> oscillation occurs

That can easily be done, through measurements and an 
understanding of basic RF systems. 

>   5. construct models of alternative VHF oscillation-suppressing circuits,
> and evaluate their effectiveness and side-effects

N7WS ran calculations and reached an independent conclusion. 
After he reached the conclusion and published an e-mail asking 
him to change his position by one of the parties in the debate, he 
was personally attacked.

Anyone doubting this can ask N7WS directly. 
 
> does not oscillate. Evaluating the effectiveness of suppressor circuits is
> a similarly-objective excersize.

It isn't that complicated. Models are useful for a system that is too 
complicated to be measured and analyzed as a real system. 
Models are shortcuts.
 
> I suspect that neither combatant is truly interested in resolving the
> underlying technical issue; doing so would terminate their righteous
> justification for continuously elbowing and needling each other. It won't
> stop until Rich publicly admits that he profits by selling unnecessary, if
> not harmful, add-ons to ignorant amplifier owners,

Profits come from more than cash. Some profits are in the form of 
notoriety. The nichrome isn't harmful, it is the theories that ruin the 
ability of people to understand the complex workings of a PA that 
are harmful. 

There are harmful mods he suggests, such as removing grid 
protection circuits. He suggests using resistors for fuses to protect 
grids. He also suggests increasing the size of equalizing resistors 
in amplifiers, when those resistors were selected to have the 
maximum possible resistance to do an effective job. Those 
changes are harmful.    

 or until Tom admits
> that he intentionally designed self-destructive amplifier circuits on
> behalf of his quality-insensitive employers and hid this malfeasance by
> using the influence of those employers to suppress Rich's whistle-blowing
> ARRL handbook article. We'll be reverse-engineering humans from their
> genomes before either of those things happens.

I suppose that could be correct. This is how it would have to have 
worked:

I would have had to have been ordered to design amplifiers to fail so 
the manufacturer's could spend extra money on warranty service. 
Dick Erhorn would have to have decided to design amplifiers that 
ate 8877's in the 80's, just like I was order to do, just so the 
companies would get returned products and service headaches, 
and lose sales.

Eimac had to be part of this conspiracy, since they covered up the 
manufacturer's intentional flaws by issuing hundreds of thousands 
of dollars of credits for defective tubes that really weren't defective.  

Eimac had so much fun doing this, they dragged it out for years 
spending millions of dollars just so we could all make Rich "look 
bad"!

or...... the case could be this:

Eimac had repeated problems with materials that they had a hard 
time curing. At first they though it was air pollution in the plant at 
Salt Lake City, then they thought it was a heat dam problem 
causing the grid to become misaligned after many thermal cycles.

What did I do? I built a tester that cycled the filaments of 8877's in 
batches of about 10 tubes. The tester had a SCR latch and a light 
bulb that detected momentary grid shorts as the filament cycled.

About 90% of new 8877's failed after two days of filament cycling, 
but I suppose it could have been a parasitic. After all, the grid had 
12 volts negative voltage on it. I suppose it didn't matter that the 
anode was at zero volts, it had to have been a parasitic!!

So here's the choice. 

1.) The entire manufacturing world has a conspiracy to discredit 
Rich, no matter what it costs. 

2.) Rich has an agenda to discredit the entire manufacturing world.  

 
73, Tom W8JI
w8ji@contesting.com

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