[Amps] Tubes vs. Solid State (was) Expert Amps 2K-FA: AnyOpinions ?

[Carl]

If you want to run serious power plus a lot of overhead margin, and be 
quiet, its hard to beat a 3CW20000A7(-;

The only noise is a small filament seal blower.

Antenna tuners are just more crap to fail, especially fancy automatic ones.

Carl
KM1H


----- Original Message ----- 
From: "Paul Christensen" <w9ac at arrl.net>
To: <amps at contesting.com>
Sent: Monday, April 30, 2012 9:56 AM
Subject: Re: [Amps] Tubes vs. Solid State (was) Expert Amps 2K-FA: 
AnyOpinions ?


>> One thing that seems to be missed in this discussion about home brewing
>> amps was clearly pointed in a comment in this thread -- the key to solid
>> state amp design is THERMAL design and protection.  Those are very
>> different skills than most amp designers of our generation learned, so
>> at least in part, it's an "old dog new tricks" problem, not a limitation
>> of the technology.
>
> Jim,
>
> Based on my experience, I agree with your comments above.  First, the
> solid-state amps I've used are not very power-stable with PA deck
> temperature.  In the broadcast industry, output power must generally stay
> within a reasonably tight tolerance.  The thermal drift from my SPE amp
> (-15%) would not qualify.  OTOH, solid-state devices have been used in
> broadcast transmitters since the late 1970s (e.g., Harris MW-1).  My
> experience in college with the MW-1 is that it was very temperature stable
> and was able to be cooled at a noise level no greater than that of a 1KW 
> VT
> transmitter.  So, perhaps in our quest to make SS amps as compact as
> possible, manufacturers are placing emphasis on size rather than noise and
> high duty-cycle heat conduction properties.  By making cabinets smaller,
> compromises are made that affect performance.
>
> Seeing output power change with temperature is not that big of a deal as
> long as the amp remains reasonably linear.  But it's an extreme annoyance 
> to
> me as is the sound of jet noise coming from the amp when I'm engaged in a
> 3-5 CW exchange.  IMO, the greatest improvements to be made to ham-class
> amps is in the area of cooling and thermal power drift.
>
> In VT amps, we can rely on high-volume designs to keep air moving at low
> sound pressure levels.  Perhaps someone can create a similar design to
> create a finned heat that allows for a high volume, but low velocity of 
> air
> to keep the PA deck cool.  No doubt, that will mean an increase in box 
> size
> at least until more efficient methods can be developed.  I believe there 
> was
> a recent QEX article that discussed next-generation SS cooling.
>
> Another factor affecting users of some VTs is that SS devices are just as
> prone to go obsolete.  If the MRF150 was to go obsolete tomorrow, probably
> enough existing Asian sources can pick up that demand since there are so
> many of those devices out in the hands of commercial, industrial, and
> military users.  But contrast that against the two-brick Tokyo Hy-Power
> design (Microsemi ARF1500).  I'm not sure there will ever be enough of 
> those
> devices deployed where it would make economic sense for an off-shore 
> company
> to pick that up.  Moreover, there may be protected intellectual property
> contained within the bricks that preclude the manufacture of the 
> devices --
> at least lawfully until such time that an active patent expires.
>
> Paul, W9AC
>
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