Great videos! Something you mentioned/tried to explain near the end: the flow resistance in the narrow evacuation tube causing a long time to bake out. A second contributing factor that you didn't explicitly mention is the volume of the vessel you are pumping out. The larger this is, the longer it will take to pump out.
The wire is AWG #22 nichrome wire. (available on ebay) The inner body of the oven is made of old propane tanks. The wire is supported on glass flanges made of pyrex capillary tubing. The resistance of the heater is set to dissipate about 500 watts at 120 volts. A thermocouple controlled voltage regulator sets the temperature. The temperature can be set to anything from room temp. to 1000 F, which would anneal soft glass fine. The controller determines the mains voltage input.
Hello! Yes! The controller for the bakeout oven shorted out one time and the temperature went up to melt the envelope! It crushed inwards until it finally blew through. Glass went down into the vacuum system. What a mess!
@ubuntupokemoninc Why would you do such a thing? Oil pumps are so available on ebay. The mercury has a vapor pressure at room temperature of about one micron. That will be the ultimate vacuum in your tube if you seal it off. I don't know if a getter will eat mercury. Stick with an oil pump using DC-704 oil. The backstream oil is burned up when you bake the tube so it isn't a problem. ron
Technically, that is true. However, the diffusion pump on the system is capable of over 200 liters per minute at the inlet. This is vastly greater than any vacuum tube volume so the major factor here is the constriction. Maybe I could make a 1 inch diameter evacuation tube! LOL!
I do not believer the getter will eat up mercury vapor. If you look at a #83 mercury rectifier it has a pool of mercury in it.for added conductivity, (it passes more current) than say a 5U4G. If I remember right the mercury in this particular rectifier tube tends to make it more noisy.
200L/min? Yea, the evacuation tube's diameter/length is probably defining the pumping speed from the tube. Unless it is particularly feasible to make that evacuation tube diameter larger, you seem to have your setup optimized as is. If you care to delve into the academics of this, search for "molecular flow of a tube". I am not sure how well water vapor follows the base theory, though.
I recently got interested in early wireless transmission. I was reading about the ground breaking work of fleming on his thermionic valve. (on the List of IEEE Milestones for electrical engineering). I found a book (
Great videos!
Something you mentioned/tried to explain near the end: the flow resistance in the narrow evacuation tube causing a long time to bake out. A second contributing factor that you didn't explicitly mention is the volume of the vessel you are pumping out. The larger this is, the longer it will take to pump out.
now i feel myself a step closer to make some glass work tubes. thanks to share your experience!
The wire is AWG #22 nichrome wire. (available on ebay) The inner body of the oven is made of old propane tanks. The wire is supported on glass flanges made of pyrex capillary tubing. The resistance of the heater is set to dissipate about 500 watts at 120 volts. A thermocouple controlled voltage regulator sets the temperature. The temperature can be set to anything from room temp. to 1000 F, which would anneal soft glass fine. The controller determines the mains voltage input.
Hello!
Yes! The controller for the bakeout oven shorted out one time and the temperature went up to melt the envelope! It crushed inwards until it finally blew through. Glass went down into the vacuum system. What a mess!
Thanks Glasslinger.
@ubuntupokemoninc
Why would you do such a thing? Oil pumps are so available on ebay. The mercury has a vapor pressure at room temperature of about one micron. That will be the ultimate vacuum in your tube if you seal it off. I don't know if a getter will eat mercury. Stick with an oil pump using DC-704 oil. The backstream oil is burned up when you bake the tube so it isn't a problem.
ron
Technically, that is true. However, the diffusion pump on the system is capable of over 200 liters per minute at the inlet. This is vastly greater than any vacuum tube volume so the major factor here is the constriction. Maybe I could make a 1 inch diameter evacuation tube! LOL!
how frowned apoun would the use of a mercury diffusion pump be?
Parts 6 are the best thing
been there done that!
I do not believer the getter will eat up mercury vapor. If you look at a #83 mercury rectifier it has a pool of mercury in it.for added conductivity, (it passes more current) than say a 5U4G. If I remember right the mercury in this particular rectifier tube tends to make it more noisy.
200L/min? Yea, the evacuation tube's diameter/length is probably defining the pumping speed from the tube. Unless it is particularly feasible to make that evacuation tube diameter larger, you seem to have your setup optimized as is. If you care to delve into the academics of this, search for "molecular flow of a tube". I am not sure how well water vapor follows the base theory, though.
have you ever had a tube implode during the suction process.
you look like marty from back to the future
I recently got interested in early wireless transmission. I was reading about the ground breaking work of fleming on his thermionic valve. (on the List of IEEE Milestones for electrical engineering). I found a book (