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-boun...@febo.com > [mailto:time-nuts-boun...@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-boun...@febo.com > [mailto:time-nuts-boun...@febo.com] On > Behalf Of Adrian > Sent: Friday, October 19, 2012 4:10 PM > To: rich...@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 > > > > > > _______________________________________________ > > time-nuts mailing list -- time-nuts@febo.com > > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > > and follow the instructions there. > > > > > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > > > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.