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Old 17th January 2010, 12:08 PM   #1
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Join Date: Jan 2010
Default Testing valves/tubes

Hi there!

My grandfather (who used to be into amateur radio and electronics) gave me a box of some old stuff he found in the roof. Included, were some reasonable looking valves (mostly NIB). As I'm into steampunk, I wanted to use some broken ones as part of a steampunk sound system I'm building into a briefcase (solid state, no way I'm putting tubes in there). Any that aren't broken I'll use for a small amplifier, and the rest donated to a local radio group or a museum.

So, my point is this. Is there any easy way to test if the valves work or not, without specialist equipment? I've got all the basic electronics gear (multimeters, power supplies etc). If it helps, I'll go through and find some part numbers. I think any without numbers I'll use anyway, they'll be too hard to identify.

Thanks for any help
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Old 17th January 2010, 02:01 PM   #2
Arnulf is offline Arnulf  Europe
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Join Date: Feb 2009
First of all, weed out any tubes that might have lost their vacuum. You will notice most tubes have silvery or brown/blackish spot inside (usually at the top for miniature tubes, at the side or bottom for larger tubes). This indicates good vacuum. If however the spot has turned into white dust (almost like kitchen salt) that means getter has been exposed to too much oxygen and the tube is bad. Firing up the heater will result in a quick relatively burnout.

Now, the second (and easy) test would be to measure resistance of the filament/heater using a multimeter. Any infinite resistance filament = bad tube.

Further tests will require a high voltage supply, heater supply and some sort of biasing arrangement (you could use simple cathode bias). This depends on type of the tube. This way you can measure emission and roughly estimate transconductance.
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Old 18th January 2010, 12:21 PM   #3
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Join Date: Jan 2010
Excellent, thanks! The tubes mostly still have vacuum, as the spots are nice and shiny. I'll look for white ones tonight. I'll also check the resistance of the heaters, although I'm not really sure which pins to test. I guess it's all different.

Otherwise, I think I'll just just exchange the probably working ones for broken ones. I assume any radio enthusiast/audiophile gets through loads.
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Old 18th January 2010, 06:44 PM   #4
Arnulf is offline Arnulf  Europe
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Join Date: Feb 2009

Download this software or refer to the online database here:

TDSL Tube search

Both contain links to datasheets with exact pinout (picture always shows bottom side of the tube, the same thing you see when you look straight into pins).
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Old 18th January 2010, 06:53 PM   #5
diyAudio Member
Join Date: Jan 2010
That's brilliant thanks! If anyone is interested, the program works under WINE on linux.
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