[Collins] Strange fix for a common problem

[Dr. Gerald N. Johnson]

Some diodes particularly germanium and schottky are point contact where 
the bit of wafer is soldered to one wire, but the other wire is etched 
to a point and held in place by pressure. In the germanium diode I think 
the junction is made where the wire touches, in the schottky there are 
tiny bits of gold that make the junction for the wire to contact. So not 
getting the contact pressure up to spec could lead to microphonics, but 
ought to be scratchy from breaking and making the connection. Not just a 
changing modulation from acoustic waves or vibration.

Another thing that is inherent in diodes is photo sensitivity. That will 
change the characteristics of a diode, both forward and the capacitance 
while biased off if the diode case is glass and not painted black. That 
could lead to a hum type carrier if the four diodes are exposed to the 
bench work light while the rig is upside down on the bench.

The four diode mod is a good one to have been done to the early 32S-1 
and KWM-2.

73, Jerry, K0CQ, Technical Adviser to the Collins Radio Association.

On 9/26/2010 4:17 PM, Glen Zook wrote:
> I just got finished working on a 32S-1 for a client.  Among other things it was very microphonic.  Often the source of this is one, or more, tubes especially in the audio section.  However, replacing the tubes did actually nothing to correct the situation.
>
> What I eventually found was that one of germanium diodes in the balanced modulator was microphonic.  Now this was one of the later 32S-1 transmitters which had the 4-diode balanced modulator rather than the 2-diodes that were present in the earlier versions.
>
> Replaced all 4 diodes and no more microphonics!
>
> Glen, K9STH
>
> Website:  http://k9sth.com
>
>
>