SB-104

[Chris Iwata]

It's very hard to find stud-mount RF transistors like the 2N6456s, they  
are obsolete. They were replaced by flange-mount transistors, and now even  
these are hard to find. If you are bent on finding replacements, RF Parts here 
 in the US is one source.  You need to buy matched pairs. They aren't  
cheap. 
 
When I blew one final on my 104, I decided it wasn't worth the cost or  
effort to get new finals or re-design the PA board.  So, I now run my SB104  
with 2 finals instead of 4 finals. This is possible by disabling the power  
combiner at the output, removing 2 finals, and re-biasing.  Morris, who  
suggested the AN782 Motorola design, is correct: The biasing scheme on the 104  
is rudimentary. The ALC also needs to be re-worked and of course you can't 
run  the same power as before. Yet, the audible difference between 50 watts 
and 100  watts unless you're in a pileup doesn't make much difference to the  
receiver of your signal. 
 
The killer of the finals is high SWR. The SB104 is far from bullet-proof in 
 this regard.
 
Chris, KL7DM 
 
 
 
In a message dated 3/28/2010 10:12:48 A.M. Pacific Daylight Time,  
ch.p49er at GMAIL.COM writes:

HELLO  ALL,
HAS SOMEONE TRIED TO REPLACE SB-104'S FINALS WITH SOME OTHERS NOT  THE
2N6456s AND IF YES WHICH WERE THE TRANSISTORS USED INSTEAD OF  2N6456s?
73
CHRISTOS PAPAIOANNOU,SV1DAF &  SV1DAF/3



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