[Top] [All Lists]

Re: [Amps] IM distortion and such

To: "Joe Isabella" <>,"Gary Smith" <>, <>,<>
Subject: Re: [Amps] IM distortion and such
From: "Tom W8JI" <>
Date: Mon, 26 Jun 2006 13:15:59 -0400
List-post: <>
> Since when does management listen to engineers??  They 
> listen to the mighty $$$$.  Just like the Space Shuttle 
> Challenger disaster chain of events, the engineers said 
> "NO!!", but management said "We'll lose millions!!", so 
> they launched with frozen O-rings.  We lost more than 
> millions...
> If you want a "perfect" amp, build it yourself.  Better 
> yet, let's all do that, swap hardware, and see how perfect 
> they are!!  Bet you a cup of coffee none of 'em are...

What people forget is amateur radio is not an unlimited 
money customer resource like commercial radio, and the basic 
use is a lot different. Commercial RF applications have deep 
pockets, Hams are cheap. Sales of amateur amplifiers are 
almost the inverse square of cost.

Because cost is a huge factor, money can't be wasted on 
things that offer no return.

A large factor is use. Amateur amps run a few hours a week 
on average. They might get cycled a few times a day. 
Commercial gear might be 24/7 52 weeks a year. The service 
difference has a huge effect on what expense pays back in 
life or reliability.

The very same things that pay back on a commercial amplifier 
are totally lost in the noise on an amateur amp.

Filament voltage is a good example. Amateur amps virtually 
never have emission failure. Amateur amps also cannot be run 
at reduced filament voltage when linearity and squeezing the 
last watt out are a concern. They aren't even remotely like 
a 4CX5000A running at 2 or 3kW with only 5000 volts on the 
anode, where the emission life is the primary source of tube 

A good engineer can sort that all out and make good 
decisions, a bad design would include things that never pay 
back. 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. They do keep this reflector busy 
by giving people something to complain about.

73 Tom 

Amps mailing list

<Prev in Thread] Current Thread [Next in Thread>