[time-nuts] HP 10811 Tuning Diode

[Adrian]

I didn't notice any damage, nor was there a visibly bad solder joint.
However, I couldn't reproduce the excess noise with a quick bench test 
at 30V / 100k neither.
DC-wise there are a few microvolts only. Same with the SMD diode.
Exept, when the original glass diode is exposed to light. With a LED 
Maglite, I got up to 50 mV (across 100 kOhm) out of it!
But there is no light shining inside of a 10811, is there?

I had first suspected a 0.1 ceramic cap, but that didn't cure the phase 
noise desease.
The diode in the original circuit appeared to be heat sensitive,
and the excess phase noise has gone away since I replaced the diode.
The noise was clearly there, and it was also there using a test adapter 
and two lab power supplies.

Adrian

Rick Karlquist schrieb:
> I wonder if the glass case got a crack in it or if the kovar seal
> was failing.  Maybe a failed solder joint (which gets fixed when you
> install the new diode). I've never heard of a noisy varactor before either.
>
> Rick
>
>
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