[Elecraft] Ten Tec never sounded so good!

[Edward Cole]

Joe,

Very interesting.  Not too surprising.

I am building a CCI HF 300w amplifier kit (Motorola Engineering 
Bulletin: EB-27A), that uses 28-volt transistors.  I bought a matched 
pair of the Toshiba equivalent for the MRF-422 (2SC2510 rated at 
150w/each; power gain = 12.2 dB).  IMD min (-30 dB) is at 85w.  The 
K3 will drive it possibly to 200w output (100w per 
transistor).  Running at 170w would probably be the cleanest 
level.  Table-I in the engineering bulletin shows Harmonic 
performance (2-30 MHz)
http://www.communication-concepts.com/eb27a.htm
http://www.communication-concepts.com/appnotes/EB27A300Sharp.pdf

If I like how the amplifier turns out, I may start building a few of 
these for the ham radio market.

Ed - KL7UW

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Message: 1
Date: Thu, 15 Apr 2010 10:20:28 -0400
From: "Joe Subich, W4TV" <lists at subich.com>
Subject: Re: [Elecraft] Ten Tec never sounded so good!
To: "'Tom W8JI'" <w8ji at w8ji.com>
Cc: elecraft at mailman.qth.net
Message-ID: <85E31A466596414D860B7AC081725221 at laptop>
Content-Type: text/plain;       charset="us-ascii"


 > For all those intent on boosting low power radios with a
 > cheap external PA, you can see measurements here:
 > http://www.w8ji.com/rm_hla-150_test.htm
 >
 > The very best the RM Italy amp gets on *any band at any
 > power* is about like a FT1000MP on the very WORSE band for
 > the MP.

If you had not documented that the transistors were only rated
for 70W PEP, I would have thought that one of the push-pull pair
was open with those results.  I don't know what transistors
are but those IM plots would suggest the bias is incorrect -
which might be logical if RM Italia are using an undersized
heatsink.

 > There is no convincing people that our 100 watt radios at
 > 100 watts are barely acceptable as is, and that all these
 > little tricks that give another 1-2 dB more power can
 > increase splatter 15 dB or more. Worse yet, those cheap
 > illegal amplifiers that make 10-watt radios into 100 watters
 > are going to be our undoing.

Very true ... we would be better off with 48V transistors
with power levels below 200W PEP.  There are several devices
capable of 3rd and 5th order IMD better than -40 dB at that
power level.

73,

    ... Joe, W4TV


73, Ed - KL7UW, WD2XSH/45
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