SB-401 Balance modulator diode replacements

[W6CUX]

The correct replacement part for a 1N34 (etal) is a 1N5711 Schottkey 
diode which started life as a hp 5800 series designed for balanced 
modulator use. Data sheet  
http://www.st.com/stonline/books/pdf/docs/3238.pdf

Mouser has these diodes as : http://www.mouser.com/catalog/628/377.pdf  
511-1N5711 at $0.10 ea.

The 1N5711 also works well in HM-102 and similar SWR detectors. A modern 
application is in the Elecraft K2/100 antenna tuner.

The 1N4148 is NOT a good replacement for a balance modulator diode.

73, Stu W6CUX

Charles W. Morehouse wrote:

> Mike,
> 1N191 diodes are hard to find.  The substitute is the 1N4148.  Mouser 
> has these.  I have used 1N34A diodes in the past.
> Get a bunch and match 4 of them.  Luck and 73.
> Wayne,
> W4GBW
>
> Michael Waldrop wrote:
>
>> Good afternoon everyone,
>>    I have an SB-401 that has 2 blown diodes in the balance modulator. 
>> The original diodes are
>>  color coded Brown/White/Brown which cross references to a 1N191 
>> crystal germanium
>>  diode I believe. I have what appears to be some 1N210 crystal 
>> diodes. They have clear
>>  glass bodies, color bands are "Red/Brown/Black". Cross references 
>> that color code  shows them to be 1N210's. Unfortunately, if the 
>> color code is correct, a 1N210 doesn't have
>>  the PIV and current rating the original Heathkit diodes has; 
>> original diodes 90VDC PIV
>>  at 500 mils where as the 1N210 has a 45VDC PIV at 27mil current 
>> rating. Even if the  210's would work I believe the internal 
>> resistance would be too high to work in a  balance modulator.
>>    Has anyone ever changed the diodes in the SB-401 and what 
>> component number did
>>  you use? I'd like to get this fixed but I don't want to install the 
>> diodes I have and have
>>  them fail.
>>    Any suggestions on diode replacements for the balance modulator in 
>> the SB-401? Thank
>>  you for any help/references/part numbers you can provide.
>>    73's
>>  Mike
>>  W5RKL
>
>

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