[Heathkit] Repost of a possibly missing message

[Duane Fischer, W8DBF]

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List Admin	


----------
From: Kenneth G. Gordon <kgordon@moscow.com>
To: Heathkit@mailman.qth.net
Subject: [Heathkit] Repost of a possibly missing message
Date: Sunday, April 11, 2004 12:03 AM






I am reposting the following message 
since I am not sure it made it the first 
time.




> My SB-101 Peaks differently on 
Recieve and Transmit - If I peak my 
> receiver at 7.2 mhz and the preselector is about the 12 O'clock position, 
> my transmit peaks at around the 1 to 2 O'clock position - This occurs on all 
> bands - I'm sure there is a simple fix for this - Any help would be > 
appreciated

 

There is NOT a simple fix for this. 
The problem is caused by what is called

{quot}Miller Effect{quot}. Since I 
cannot remember exactly what this is, I won't try to

describe it, but any really good book 
on vacuum tubes, like Terman's, will 
cover it in detail.

 

Basically, the fact that you are using 
the exact same tuned circuits with two

completely different sets of tubes, 
causes the problem. Those tuned circuits

peak the receiver RF amp and Mixer 
stages, and the final amp driver and 
last transmitter mixer.

 

Heathkit had a fix which while not 
really trivial, is not really all that hard

to implement either. It involves adding 
two (or four) small adjustable padders

in parallel with the tuning capacitors 
which are switched in for receive, and

out for transmit, or vice versa, probably 
via small switching diodes.{#160} Here is a 
link to a URL which includes this mod:




 
http://home.comcast.net/~wa3rey/wa3rey/hw100.htm



, courtesy of one of our list members.

 

BTW, this fix was FIRST published 


magazine about the time the SB-101 



owners of an SB-100/101/102 to install. 



 

There is also an RIT mod for those 


 

Ken W7EKB




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