[time-nuts] HP 10811 Tuning Diode

[DaveH]

Back in the dark ages while dinosaurs roamed the earth, I worked for a music
audio company outside of Seattle, WA called Tapco (they are now Mackie).

They were making PA amplifiers and I and three other people were doing final
test and burn-in. 

Had one that had a bit of a 60Hz hum on the output. I took the cover off and
the hum went up. Reached over to grab a scope lead and the hum died back
down.  Turns out one of the plastic transistors had a bubble in the case and
the fluorescent lighting was hitting the junction.

DaveH 

> -----Original Message-----
> From: time-nuts-bounces at febo.com 
> [mailto:time-nuts-bounces at febo.com] On Behalf Of Bob Camp
> Sent: Friday, October 19, 2012 13:20
> To: 'Discussion of precise time and frequency measurement'
> Subject: Re: [time-nuts] HP 10811 Tuning Diode
> 
> Hi
> 
> The normal 10811 package has several openings in it. Light 
> *might* get in
> there. A "micro volts" level of noise can mess up your phase 
> noise if it's
> AC noise at a low frequency. 
> 
> Bob
> 
> -----Original Message-----
> From: time-nuts-bounces at febo.com 
> [mailto:time-nuts-bounces at febo.com] On
> Behalf Of Adrian
> Sent: Friday, October 19, 2012 4:10 PM
> To: richard at karlquist.com; Discussion of precise time and frequency
> measurement
> Subject: Re: [time-nuts] HP 10811 Tuning Diode
> 
> 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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> 
> 
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