[Milsurplus] Germanium diodes

[Jim Whartenby]

Greetings Ray
Are you satisfied that the input to the discriminator is correct?

I honestly have not seen a problem like you have described in PN
junctions, but I am by no means an expert.  If the diodes check with a
10:1 ratio or better with a VOM, I would suspect that they are OK.

There is the problem with reverse current in germanium at elevated
temperature, so if the ARC-38 is getting quite hot, that would explain
some of the problems.  Is there enough air circulating to keep the
chassis cool?


In reply to Elden's comments:
I don't think that the url you listed is implying that the germanium
transistor is destroyed but that at high temperature the minority
current (leakage current) becomes significant.  Once back at normal
operating temperature, I would think that normal transistor operation
is restored.

As a kid I use to play 9 volt powered germanium radios on 12 volt car
batteries.  Radio would work fine for a while but then would stop
playing.  Once it cooled down again, it worked fine.

It would be interesting to see if age is having an effect on PN
junctions.  We already know that vacuum tubes close to 100 years old
still work!
Jim

--- elden meyer <elden_meyer at yahoo.com> wrote:

> Germanium transistors in early auto radios were
> subject to failure from re-diffusion:
> 
> Time and heat can have the same effect on diodes.



--- Ray Fantini <rafantini at salisbury.edu> 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