That's exactly what I'm doing. I've got two glass vacuum jars and one steel. I'm playing with different types of foam - rigid vs. flexible, various types, etc . I haven't tried the aerosol foam yet. I understand that once you start to use the can it has a very limited shelf life. I did see one type that has a temperature limit high enough to officially be used for this application. Ed On 7/30/2011 2:11 PM, Don Latham wrote:
I've tried simply buying thermos flasks of appropriate size. The ones for soup have wide mouths and are glass. Cheap, too and you can improve the tops and pull wires very easily. Foam insulation comes in aerosol cans for plugging cracks around your windows etc. Don J. Forster I would avoid steel. It usually has higher thermal leakage than glass. I'm rebuilding an Oscilloquartz 8601 oscillator that has a smashed Dewar. The 8601 is basically the same as an 8600, but with a different connector arrangement. Since I can't replace the original Dewar, I'm trying various vacuum flasks to see which one works best. The differences are related to the size (how much room for a foam plug) and material (glass vs. steel). Am I correct in thinking that 'best' means minimizing the current drain? Yes, but you maqy not want to cut the leakage too much below what was originally there. It could cause loop overshoot or instability. I'm thinking that minimizing the current drain means minimizing heat loss to the external environment and therefore most stable performance. Only if the loop can handle it. Or should I try to match the thermal characteristics of the original flask and plug? I could approximate this by adjusting the thermal characteristics to obtain the same current drain as stated in the specifications. That will give you a static match, not necessarily a dynamic match. Consider if you filled the Dewar with mercury. Of course, if you go too far in reducing the current, the oven could overheat. The oscillator includes a precision thermistor to monitor the temperature of the oven to prevent this. Any comments? Ed Good luck. -John _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
