SB-401 crystal diodes - Heath Part No. 56-26-1

[Garey Barrell]

Rob -

Based on when the SB-401 was designed, it's much more likely that those 
diodes are germanium.   They "MAY" have been selected, but not likely.

Today it's fairly easy to "match" Hot Carrier diodes with a DMM on 
"Diode Test" function, which actually measures forward voltage drop.  
Diode manufacture today is such that you could probably just put four 
diodes selected at random and they would be close enough.

You can also buy "matched quads", although you would probably be 
discouraged by minimum order requirements.

If you only have "one" bad one, you could take the relative power diode 
and use it in the quad as a sub, then replace it with a 1N270 or other 
germanium diode or any of a number of Hot Carrier diodes.  Even a 
silicon 1N4148 would work fine in the relative power function.   The 
diode balanced modulator affects carrier suppression primarily, so as 
long as carrier suppression is adequate you're ok.   It's  _possible_  
that the balance components will need modification because of different 
diode capacitances, but not likely.

73, Garey - K4OAH
Atlanta

Drake C-Line Service Manual
<http://hr99.home.mindspring.com/R-4C_Servicez/> 



Robert Myers wrote:

>Hello all,
>
>I am in need of some crystal diodes used in the SB-401 on the carrier
>generator board -- part of the balanced modulator.  They are named D101,
>D102, D103, and D104 there.  And under the chassis, one more of the same
>(D9) is used to pick off the final RF output to measure relative power.
>
>Heath Part No., for each is 56-26-1.
>
>I believe they are a matched set of hot carrier crystal diodes, but I'm not
>sure.  Does anyone know the generic part number for these?
>
>Does anyone have a spare(s) to sell?  Or know where I can get them?
>I just need two to experiment with.  Or even just one would do.
>
>Thanks,
>--- 73, Rob Myers
>        VE3JQL
>
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