----- Original Message -----
From: "Tom Rauch" <w8ji@contesting.com>
To: "Edwin Karl" <edk0kl@centurytel.net>; <amps@contesting.com>
Sent: Thursday, September 27, 2007 7:45 AM
Subject: Re: [Amps] Amps Digest, Vol 57, Issue 52
>
>> Re: Amplifier Linearity
>>
>> Does anyone besides me still use a 'scope in trapezoid
>> pattern looking
>> at input vs. output linearity?
>
> Not really, because a scope tells us very little about the
> quantity of splatter.
> It might be a tuning aid for those who don't know how to
> tune with meters, but it really isn't a good bandwidth
> indicator.
>
>> Seems like we're getting into "flat topping" tubes, etc
>> just to get the max.
>> output level etc.
>
> It's actually pretty tough to flat top a tube when you tune
> it correctly. Especially compared to a semiconductor like a
> bipolar transistor.
>
> Tubes generally have a very high current saturation point
> and remain reasonably linear up to that point, especially in
> grounded grid systems with the inherent high levels of
> negative feedback. They don't happily live at 500 watts and
> suddenly fall apart at 550 watts, the exception being grid
> driven sub class 1 tetrodes that suddenly move into sub 2
> (grid current) or fall out of screen limits. But a triode in
> GG remains pretty clean long after rated power is passed if
> the amplifier is tuned correctly and if there is no positive
> feedback or regeneration.
>
> That's in stark contrast to bipolar transistors or AB1
> tetrodes, which can fall apart dramatically before the
> meters tell you something is wrong. For example you see the
> CB Hams shorting ALC lines on rigs or turning up the power
> limit pots inside radios to make 100 watt radios run 120 or
> 150 watts. This makes transistors and some grid driven
> tetrodes increase IM expotentially where the user might pay
> a 15dB penalty in IM performance (splatter) for a 2 dB
> increase in power.
>
>> All the "it can't happen here" talk is really counter
>> productive. If a guy
>> says
>> he can do it for heaven's sake let it go. Please don't try
>> and prove how
>> clever you
>> are. It just doesn't impress me and wastes my time.
>
>
> What doesn't impress me are grumpy people who take
> everything personally, and who think just because something
> works it is a good engineering practice. That's most common
> with antennas, and largely why people learn so slowly when
> dealing with antennas. Of course that is also why they are
> so much fun, because when we are emotionally involved it is
> like a romance.
>
> Unfortunately what that does is stop people from thinking
> and encourage living by pure emotion. It also makes me think
> RF or too much fat meat and beer damages brains and makes
> Hams grumpy old bitter farts with narrow minds and big
> butts. :-)
>
> 73 Tom
There is some very good technical information buried in that post Tom. Ive
edited it for future use to silence some naysayers.
BTW, what is your waist size these days? And you certainly are no youngster.
I can happily report a 34" waist, I havent had a drink in almost 8 years, I
limit my meat intake and work out daily. My blood pressure is normal as is
my chlorestrol, heart, and prostrate. So I know you couldnt have been
referring to me. It has always been my dream to die happily in bed at 80+
with a 20 something hot blonde; female that is.
My doctor doesnt get rich from me either.
Carl
KM1H
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