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Old 1st February 2012, 05:36 AM   #1
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Default Resurrecting old tubes

I was given a box of old tubes sometime back and over the last day or 2 I've been running them thru' the tube tester (AVO MKIII) to see what were bin jobs and what should go on the shelf.

There were about 20 807s in the box. Of these about 12 tested good except for bad heater/cathode leakage. It was suggested to me that this was probably due to moisture and dirt ingress into the bases. I tried cleaning up the exterior of bases with Isopropyl Alchohol. That did'nt help.

Is the suggested problem just wrong or would I need to remove the bases and clean inside them to get any noticable improvement. This seems a lot of work so I'm asking advice before I try.

Not worried about doing irreversable damage while doing this, the tubes are'nt usable as is.

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Old 1st February 2012, 05:54 AM   #2
Enzo is offline Enzo  United States
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Moisture in the bases? perhaps putting them in a heated environment for a time. In a very slow oven maybe or just heaters energized while sirring in an enclosed space. Cook the moisture out.
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Old 1st February 2012, 12:34 PM   #3
ryuji is offline ryuji  United States
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running the tubes for a few hours at higher then running voltage on just filament to keep them really warm could probably get most of the 20 tubes in workable condition, gives the getters a chance to soak up the gas
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Old 1st February 2012, 01:33 PM   #4
Doz is offline Doz  United Kingdom
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I had 1625's the same. Oven sorted them out.
"To err is human.. to make a real balls-up requires a computer"
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Old 1st February 2012, 02:00 PM   #5
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807 has a 5-Pin Base. If we count the two heater Pins as one (because they aren't insulated from each other), then we have 4 Pins. These can be permutated in the following ways: ∑ 1 to 4 = 1+2+3 = 6 ways.
Heater Cathode failure is one of these possibilities (probability = 1/6)
All your 12 Tubes have that problem. 1/(12*6) ~1.4%
Seems a bit strange, doesn't it ? Would be much more likely when there would be some other insulation failures, too.
Maybe some kind of intelligent moisture (Creationism !) which only looks for the heater and cathode pins.

Well, what I want say. It is very likely that these tubes were sorted out because of f-c insulation failure. Furthermore when you already had sorted out the other 8 which tested bad.
So, either you throw them aways or use fixed bias or use seperated/insulted heater supplies.
Терпенье и труд все перетрут
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Old 1st February 2012, 07:59 PM   #6
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and certainly....check the calibration of the test equip if everything is testing with leaks or shorts.
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