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[Amps] Why hasn't solid state replaced tubes?

To: <amps@contesting.com>
Subject: [Amps] Why hasn't solid state replaced tubes?
From: wc6w at juno.com (Radio WC6W)
Date: Mon Mar 3 12:35:36 2003
On Mon, 03 Mar 2003 10:53:29 -0500 Pete Smith <n4zr@contesting.com>
writes:

Hi Pete,

> This all makes sense to me, but I was a little uncertain about Tom's  
> comments about tubes being on the way out.  It seems to me (as a
layman), 
> that high-power solid state amplifiers for amateur use haven't come
very 
> far since (pardon the phonetic spelling) Helge Granberg's cover article
in 

   Your spelling is correct... rather than phonetic!   :-)

> QST maybe 25 years ago.  There still is no legal-limit solid state
amateur 
> amplifier that I know of, and the existing hardware all seems to
require a 
> 50-ohm load, is intolerant of operator errors, fragile, etc.  I wonder
who 
> will be the first to come up with a solid-state rendition of the Acom
2000A 
> -- 1500 watts output, full autotune, complete protective circuitry, and
so 
> on.  Could that be done today for the same price as the Acom, or are
the 
> transistors and other bits still too expensive?

   Doubtful. 

   For 1500 watts out it would take say... 4 - MRF154's.  Those probably
would cost at least $1000 at an OEM level, now that Tyco (with all those
legal bills to pay!) owns AMP, who bought M/A Com, who now owns the
Motorola low freq. power FET product line.

   A real output matching network (double pi-net?) rather the simple bank
of low pass filters typically employed in conjunction with this type of
amp. might actually result in some cost savings as well as the ability to
provide full output into something besides a perfect 50 ohm load.

   There are some concepts that could be used to good advantage in the
power supply of such an amp:

   For instance, if the unit was run .... Class H, I believe is the
correct terminology, with a dynamically variable (switching) power
supply, a lot of the heat normally generated in a transistor unit could
be avoided.    I believe that Collins used this technique in an airborne
(VHF?) transmitter back in the 1970's.

   Using the RF input/output transformers for line isolation permits the
use of a direct off-line power supply;  Saves a large transformer.

   Though, still no way around the pile of $$ for the RF transistors... 
so the thing would probably have to retail for $8-10 kilodollars.

   May I take your order?  :-)

> 
> 73, Pete N4ZR

73 & Good morning,
   Marv WC6W






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