[MRCA] Germanium diodes

[Doran Platt]

Ray Fantini wrote:
> Anyone have any ideas about the affects of age on Germanium diodes? starting to suspect that several of the diodes used in the 618S/ ARC-38 family of radios I have been working on are failing to provide sufficient voltage to work properly. they work in discriminator circuits to provide reference voltage to servo amplifiers. The newest ones are from 1959/60 so they are over forty years old and do not know if their internal resistance increased with age? 
> Ray Fantini KA3EKH
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Ray,  Interesting that you mention this subject.  I operate a couple of 
GRC-19B's here in the station.  The TM states that the discriminator 
diodes should be checked "regularly" to ensure operation and match.  
Both my units exhibit some tuning sluggishness, especially when operated 
at less than 28 volts, a not uncommon situation with many GRC-19's.  
Setting the voltage to something around 29 volts appears to help but may 
mask the real problem(s).  I'm going into both mine to determine if 
diodes might be the problem. 
Given that the problem is not uncommon and the fact that the servo 
systems in these units (both Collins design) are quite similar, the fix 
may be applicable to both systems.  BTW, if you ever need a replacement 
chopper, I have what I believe are the correct ones.  Finally, please 
let us all know what you find out with your ARC-38.   Regards de K3HVG