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[Amps] New 2 PA design

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Subject: [Amps] New 2 PA design
From: "Jim Thomson" <jim.thom@telus.net>
Date: Sun, 17 Oct 2010 00:42:15 -0700
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Date: Sun, 17 Oct 2010 07:57:05 +0100
From: "David Cutter" <d.cutter@ntlworld.com>
Subject: Re: [Amps] New 2 PA design

I'm drifting off topic a little but is it not preferable for heat transfer 
purposes to run several lower power transistors in parallel to reduce hot 
spots?  There is also the opportunity to have redundancy, ie if one in a 
string dies, the amplifier can still work.  The transistors will also be 
significantly cheaper.  Matching input and output will be more difficult but 
the robustness obtained is more desirable than minimum parts count.  The 
layout will be more of a challenge to achieve the highest frequencies. 
Perhaps from a commercial point of view this is less desirable but for home 
builders easier to achieve high power in a small space, which will become 
the dominant restriction.  Water cooling is a lot quieter and smaller than 
fan cooling : - )

David
G3UNA

##  AL  conducts heat aprx .57 as good as CU.  [CU=1.0 ]
## OK, lets say u get this 1.5 kw output wonder bar SS amp running. Now
you require the mating 2kw auto tuner to go with it.  You also need the mating
power supply to run the amp.  I think you just lost it right there  with the 2 
kw
auto tuner requirement.  If you opt for a manual 2 kw tuner, that just defeats 
the SS amps'  rapid band change, no tune advantages.   If you use a bunch of 
low 
power devices, then you need a mess of combiners.   What is the imd on these
SS amps like?   So far, from what I have seen, most are not all that great.

##  IF you want to run the 1.5 kw output SS amp at less power, say 750w  for
rtty,  how do you achieve this, without having lousy eff ?   Ur typ 200 w SS 
[50%]
ham xcvr has lousy eff  when run at 150w out..and really lousy at 100w out.[36%]
At 50w out, they are a joke.    Perhaps what's needed is some way to reduce the 
Voltage a bit, like down to 70% of normal.  Dunno if that will degrade imd or 
not. 
Meanwhile, the  YC-156  will clean it's clock 5-8 times over. 

Jim  VE7RF


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