[Elecraft] QRO

[Brian F. Wruble]

 I have always wanted to try building one of those big amplifiers. One thing
that stops me is that I have no idea where you get or how you build all the
"sheet metal" parts --- complicated pieces of chassis, etc.  Anybody out
there who knows how people manage to build or source these?

Thanks.  73 de Brian W3BW

-----Original Message-----
From: elecraft-bounces at mailman.qth.net
[mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Vic K2VCO
Sent: Monday, May 22, 2006 12:40
To: michael taylor
Cc: elecraft at mailman.qth.net
Subject: Re: [Elecraft] QRO

michael taylor wrote:

> I'm curious, what makes RF amplifiers fairly expensive projects? 

Tube amplifiers are expensive because high power components (HV variable 
capacitors, high power bandswitches, power transformers, tubes, sockets, 
etc.) are expensive.  In addition, although the basic circuit is quite 
simple, ancillary circuits to protect the expensive parts and provide 
functionality like QSK and automatic tuning are needed.  Finally, the 
enclosure is large and must be well-constructed to be RF tight.  A 
homebrewer can build an amplifier relatively cheaply by using surplus 
Russian tubes and scrounging parts.  But you need to know what you're 
doing, since mistakes can be fatal.

Transistor amplifiers are expensive because they are more complex.  A KW 
amplifier may have 8 power transistors, and the protective circuitry may 
be more complicated than that for a tube amplifier.  If you know that 
you will be driving a 50 ohm load, automatic tuning is simple; just 
switch in the appropriate lowpass filter for each band.  However, 
transistor amps are unhappy with even a low-to-moderate SWR, so a 
built-in antenna tuner is really needed.
-- 
73,
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco
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