[Central-Electronics] CE20 oscillator drift

[Jim Candela]

Hi Gang!

A few years back I tried several old CE 9 Mhz crystals in my 20A. They all drifted anywhere from 150 hz to 600 Hz over the first hour turned on. I want to buy a new crystal, but most that I've seen are around $20 or more. I have thought of adding a PTC heater to the crystal, maybe a thermistor like what we use to protect a tweeter, looking for a transition temp around 50 degrees Celsius. This could be powered by the filament voltage to act as a poor mans crystal oven. Could also use a real oven from an old VHF transmitter. I also wonder if the 20A oscillator has unusually high crystal current.

The Reflector has been quiet lately...
Jim
WD5JKO


________________________________
From: Tom Elmore <tom at telmore.com>
To: k6jek <k6jek at comcast.net>; central-electronics at mailman.qth.net
Sent: Friday, August 26, 2011 5:55 PM
Subject: Re: [Central-Electronics] CE20 oscillator drift

John, could it be the crystal has aged sigifcantly too?




-Tom / KA1NVZ

-----Original Message-----
From: k6jek [mailto:k6jek at comcast.net]
Sent: Friday, August 26, 2011 02:42 PM
To: central-electronics at mailman.qth.net
Subject: [Central-Electronics] CE20 oscillator drift

Have any of you tackled the 9 MHz oscillator drift in the 20A? I measured it yesterday. At T+35 it was skidding along at 45 Hz every ten minutes. It was still moving about 25 Hz every ten minutes after 65 minutes of warm up. It settled down nicely after two hours having moved about 300 Hz from power on +5 minutes. Today I tried keeping things cool. I installed one of those Weber 5U4 replacements instead of the real 5U4. I placed a very slow fan on top of the cabinet drawing out, a 220 Hz muffin plugged running on110. This made things worse. The overall drift was less but it was still moving after four hours. I'd hoped it would stabilize at a lower temperature and do that sooner. No dice. I guess all I did was slow down the oscillator heating process.Incidentally, those Weber solid state rectifiers get plenty hot themselves. I'd guess there's a big resistor inside along with a couple of diodes.My thoughts are turning to negative coefficient capacitors and
 even to crystal ovens
. Either that or to heck with it.Jon, K6JEK______________________________________________________________Central-Electronics mailing listHome: http://mailman.qth.net/mailman/listinfo/central-electronicsHelp: http://mailman.qth.net/mmfaq.htmPost: mailto:Central-Electronics at mailman.qth.netThis list hosted by: http://www.qsl.netPlease help support this email list: http://www.qsl.net/donate.html
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