posted on August 13, 2002 09:37:54 PM new
Is there a way to test old vacuum tubes to see if they are still good? Can you tell by looking at them? Any help would be appreciated because I don't want to sell someone vacuum tubes that don't work!
posted on August 13, 2002 10:18:40 PM new
You can't tell by looking at them. They have to be tested. One way you can tell if a tube is bad is to do a continuity test through the filaments with an ohmeter (you will need a book that gives pinouts to do this. Radio shack used to cary these books). If there is no reading, the tube is bad and can be thrown out. If there is a reading, you still can't tell if it's good without further testing, which requires a tube tester. Your best bet for a tube tester is a swap meet. Anyone who has one up for sale probably doesn't know what they have and you can pick it up for a song and dance. Anyone who has one that they use(like myself) wouldn't part with it. Just make sure any one that you buy has the tube chart with it. It's worse than useless without it. A tester is a good investment if you plan on selling a lot of tubes. The right tube can be worth a small fortune. After you get the tubes tested and sold, you can list the tester on Ebay and make a nice profit. The last one I sold went for over $250.00. I picked it up at an auction for $5.00.
The light at the end of the tunnel will turn out to be an oncoming train.
posted on August 14, 2002 12:17:07 AM new
Thanks for the reply! I'll only be able to test the tubes with an ohmeter with no pinout book. I guess that as long as each pin has continuity with at least one other pin, it should be ok. Right?
posted on August 14, 2002 08:51:42 AM new
Actually, when testing with an ohmeter, you want to check the filament (heater). If that is bad, it will not work. If it is good, it means it will glow when power is applied in a circuit, but some of the other components can still be weak or bad. The ohmeter test will allow you to cull out the tubes that are positively bad, leaving you with a batch that need further testing. If you are acquainted with a ham radio operator, he/she will probably have a book with the pins identified and possibly a tube tester you could borrow.
The light at the end of the tunnel will turn out to be an oncoming train.
posted on August 15, 2002 09:51:24 AM new
Search ebay for tube manual. Get one of the newer editions so you won't miss some of the last tube types made. Also the new ones are less collectible so are cheaper. If you've got lots of tubes you can buy a tube tester, too.
The idea of looking for continuity from all pins won't work, you need to know which pin goes where. The elements in the tube are insulated from each other and separated by vacuum. Some pins are internally connected to others, and some do absolutely nothing.
As mentioned, a working filament is not the only requirement for a working tube, but if the filament doesn't work you can be sure the tube is bad.
posted on August 15, 2002 05:40:53 PM new
Several months ago I sold a bunch of vacuum tubes on Ebay, and just said I knew absolutely nothing about them and had no way of testing them. I was surprised how well I did, and never had a complaint. When I asked some of the guys if the tubes worked, they most often said they didn't care, because they were just collecting them as self sitters anyway. If you are just honest about it, most people will take a chance. I found grouping the same tube numbers worked also. I figured at least some of them would be good if they were getting several of the same. And, I found the radio and vacuum tube guys to be a really nice group and so helpful. Good luck!
