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Re: [Amps] IM distortion and such

Subject: Re: [Amps] IM distortion and such
From: W2RU - Bud Hippisley <>
Date: Mon, 26 Jun 2006 20:30:43 +0000
List-post: <>
Tom W8JI wrote:
> One of the best engineered amps on the market was the 
> SB220. It was amazingly cheap for the results, and they had 
> a very good service life when operated according to 
> manufacturing specs. That amp is a prime example of good 
> engineering for the market place.
> By the way, when all the patches and fixes that are touted 
> as life-improving mods are added to an amp in amateur 
> service the primary failure mechanisms will still be 
> uncontrollable. All those cost adding mods wouldn't do a 
> thing in the big picture.

With respect to Tom's first paragraph above:  I still have the SB-220 I 
built more than a quarter of a century ago.  I think I've replaced a 
grand total of one tube in all that time, despite pounding it to death 
in contests, DXing, and general operating over the years.  During that 
period, I have transmitted into the wrong antenna or no antenna more 
times than I care to remember.  it still has the original cooling fan 
and it's the quietest legal limit amplifier I've ever owned, used, or heard.

With respect to Tom's second paragraph above:  Once upon a time I owned 
an ETO PA-76.  I didn't keep it because it kept "breaking" despite the 
(excessive) control circuitry in it.  I currently also own an AmpSupply 
LK-550 (to operate 160) and its unnecessarily complex interlock 
circuitry frequently keeps the Operate / Bypass relays from energizing 
when requested.  One of my pending shack projects is to "gut" the 
control section of this amplifier so it approaches my SB-220 in 
simplicity and reliability.

For *me* (and I emphasize "me"),  3-500Z amplifiers represent the best 
available combination of reliability, resilience to dumb operator 
errors, tube (valve) replacement cost, TVI minimization, and required 
drive levels (relative to my favorite transceivers) for amateur MF/HF 
amplifiers.    After my first PL-172 failure, I used to cringe every 
time I turned on my old HT-33A, and I developed similar reactions to 
firing up the PA-76.    By contrast, I don't live in fear of energizing 
my SB-220, and it is, consistent with remarks by both Tom and Rich at 
one time or another, one of the best values I've ever found in any of my 

Bud, W2RU

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