[MRCA] Germanium diodes

[J Forster]

Are you sure sluggish operation at lowered voltage is not due to drying out grease. Generally the torque of motors increases with supply voltage, and dried out grease would need more torque to operate.

It is possible older diodes may deteriorate. Can you do a V-I plot on a curve tracer. I'd suspect they are more likely to go leaky than anything else.

FWIW,
-John



Doran Platt wrote:

> 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
> >
> >
> >
> >
> 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