SB-401 Balance modulator diode replacements

[Chris Iwata]

I've been reading all the replies to this question: Here's my two  cents....
 
Best replacements are Schottky diodes.  Reason is they are easier to  match, 
have lower capacitance, and better temperature characteristics.   Forward drop 
is similar to Germaniums, about 300mV, as opposed to 1N4148 or  1N914 which 
are Silicon and have forward drops around 600mV.   If you  use silicon diodes 
you'll need higher drive levels to overcome the forward  drop  (barrier 
potential).  Also Schottkys have sharper dynamic  resistance curves which means they 
act more like switches than other  choices.
 
But, many Schottkys have low PIV ratings, some as low as 7 volts.  A good 
choice would be 1N5711 which has PIV around 70V.  Most mixers  (balanced 
modulators) won't see anything like that kind of reverse voltage  anyway.
 
Matching means at least finding four diodes (I assume SB401 uses four  
instead of two) with forward drops that are as close to equal as possible.   
Theoretically matched means matching the dynamic characteristics, but that  requires 
a curve tracer.
 
Truthfully, in a balanced modulator if you can null out the carrier in  
absence of audio input, it's likely gudenuff !
 
Chris KL7DM
 
 

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