"Life Test" on Used Tubes

[zombiwoof]

I have been buying a lot of NOS and used tubes on Ebay, I've been careful to check the posted specs the vendors give and have been pretty lucky on the used tubes, I've gotten some really good stuff for as little as $.99 to $4. I've noticed that a lot of people bid higher on the name-branded tubes, but you can get rebranded RCA, GE, Mullard, etc. for great prices because many don't understand the rebranding thing.

When I get these tubes, I always check them on my Sencore emissions tester for emissions, shorts, etc. and do the "life test" to see how worn out they are. I've had a couple of rec tubes and a pair of Mullard EL34's that tested good on emissions and shorts, but failed the life test (dropping the voltage knob one click and see if the needle moves down). Should I go by the tester instructions and "reject" these tubes outright without trying them in my amps? I figure the rec tubes would be an iffy proposition if used, they might cause problems, but I assume that the EL34's would probably be all right to use if they sound OK. What do you guys think?

By the way, one of those rectifier tubes was sold as NOS, yeah right!

Al

[slider313]

I make it a point not to buy used power tubes. Most tube testers test at wall or line voltage. Your amp will run them at 3-4 times that.

[SatelliteAmps]

Life Test usually is not a good indicator of life left in a tube.

[jcs]

i screen all of my tubes 1st, but the life test needs to take place for 5-10 minutes to fully display any shorts..

the guy i bought my b&k 600 removed the spring from the life test button so it could be held in place for 5-10 minutes without having to hold it down with your finger..

holding it down for 10-15 seconds is NOT going to fully display shorts and the b&k 600 is considered to be one of the top emissions testers,many repairman relied on b&k 600 for mobile testing out in the field..

i also retest the power tubes IMMEDIATELY after running in a live amp while they are still hot and under stress, i have never had any issues testing this way in addition to testing with a b&k 707 mutual conductance tester.

used power tubes need to be set up and current measured in a live amp for several hours of playing time.

of course testers like the maxi matcher test power tubes at full operating volts..

[zombiwoof]

i screen all of my tubes 1st, but the life test needs to take place for 5-10 minutes to fully display any shorts..

the guy i bought my b&k 600 removed the spring from the life test button so it could be held in place for 5-10 minutes without having to hold it down with your finger..

holding it down for 10-15 seconds is NOT going to fully display shorts and the b&k 600 is considered to be one of the top emissions testers,many repairman relied on b&k 600 for mobile testing out in the field..

i also retest the power tubes IMMEDIATELY after running in a live amp while they are still hot and under stress, i have never had any issues testing this way in addition to testing with a b&k 707 mutual conductance tester.

used power tubes need to be set up and current measured in a live amp for several hours of playing time.

of course testers like the maxi matcher test power tubes at full operating volts..

I'm not talking about matching tubes at all. On my Sencore emissions tester, there is a knob position for checking shorts, that's different than the life test. For the life test, you drop the knob that sets the voltage to the tube from the proper setting to one setting less, and check if the needle drops from the good area to the bad one, or if it drops at all, even if it stays in the good area. If it drops into the bad area, the manual says to reject that tube. I'm just wondering if I should take that advice and not even consider using a tube in my amp if it drops into the "bad" area, or if it would still be safe to use the tube even though it apparently is pretty worn out.

Al

[zombiwoof]

Life Test usually is not a good indicator of life left in a tube.

Are you saying that a tube that fails the life test might really be a usable tube?

Al

[jcs]

on my b&k 600 the life test puts the tube under load,after this test the tube is good and hot and more stressed,then i check all of the other parameters following this test..

i highly recommend you install the tube in a live amp for a final test then put it back in the tester while warm and recheck everything.

i also test everything on 3 different testers,its a pain in the arse and it takes time but i dont want to take chances especially with power tubes..

also make sure your tester has warmed up for at least 10-15 minutes.

[SatelliteAmps]

Are you saying that a tube that fails the life test might really be a usable tube?

Al

No, I'm saying that the life test on most testers is not a great test that shows much of anything when dealing with guitar amplifiers.

If a tube fails any test on most testers then it is pretty much a bad tube.

[Blue Strat]

I'm not talking about matching tubes at all. On my Sencore emissions tester, there is a knob position for checking shorts, that's different than the life test. For the life test, you drop the knob that sets the voltage to the tube from the proper setting to one setting less, and check if the needle drops from the good area to the bad one, or if it drops at all, even if it stays in the good area. If it drops into the bad area, the manual says to reject that tube. I'm just wondering if I should take that advice and not even consider using a tube in my amp if it drops into the "bad" area, or if it would still be safe to use the tube even though it apparently is pretty worn out.

Al

If it sounds good and doesn't produce a discernable volume drop it's ok to use.

[zombiwoof]

Thanks for the info guys!

Al