how do you know a bad tube?

How ironic the timing for a personal delima. Last nite I turned off my pre-amp fist and got a right side pop in my speaker. Since I hadn't turned off my amp 'it had to be as a result of something in the pre'.

Switched tubes from side to side as I had suggested. No change! Then I went to the amp and switched one of the sets of small tubes. Not only did the pop leave the right channel it left the system (for now anyway). If I had a tube tester I could probably test it and detect some imbalance that I can't hear in use. I'm not sure if that is a loss.

Back in the days I was frugal and thought my tubes would (should) last forever I had a spare tube of each type set aside for testing. Then when I changed tube sets I had lots of tubes available for testing as well as spares.

My biggest fear about owning a tester is just imagine how anal you could get about tube condition and how much time you could spend monitoring their condition. Oh, my. Got enuf on my plate worrying about things like set-up etc with out taking on that responsibility.

Have fun, it ain't really a big deal. I am as dumb as a stump, even if I don't appear to be so sometimes. :-)

Newbee,

The act of turning off a component, often results in noise, without any component necessarily being defective. That is why one should not turn off sources or the linestage/preamp first, because any such transient "pop' will be amplified by the power amp, perhaps to destructive levels.

Sometimes noise in tubes is eliminated by the very act of pulling and reseating the tube. Often noise comes from poor contact at the pins, other times, something deposited on a surface inside the tube can be shaken loose and the source of noise eliminated.

Perhaps the best reason to have a tube tester is not to find out if a tube is beginning to go bad, but rather, to determine if a new tube is safe to use at the outset. I own a tester and lent it to a friend. The tester determined that one of the rectifier tubes he was keeping as a replacement showed no voltage drop in either direction (shorted); it is frightening to think what that tube would have done had he inserted into an amp.

Jaybo
OK... i GIVE UP. Wadaya mean? they could wink, blink, and nod for all I'd know. I can't look them in the eye either. So we are eeven.

I did learn one good thing just a few moments ago... the upcoming preamp uses "two" types of tubes... not three. Whew! two 12AT & two 12AX. From the maker all four are but $125. having heard it with stock tubes, it suited me as was.

Newbee

"My biggest fear about owning a tester is just imagine how anal you could get about tube condition and how much time you could spend monitoring their condition."

you're supposed to monitor them too?

Sweet god. and I thought I had this near licked. I'll do my best to restrain myself. Once the lid is on, as you said, there's enough left to futz with without doing that too.

Larry
it matters not how I go about it... I always get a wee bit of a pop. bigger if I shut down the pre first though. I don't do that anymore. but there still is a little pip.. nothing like a serious P-O-P! though.

More than you ever wanted to know about tube testers:

http://tone-lizard.com/Tube_Testers.html

As far as acquiring one you will have to search online for a price in your range that meets your needs. Read up first so you are knowledgable about what you need/want. It is easy to overpay but bargains can be had.

As far as the gauge size issue I would recommend a magnifier
of some sort since I know of no tester designed to accomodate the visually impaired. Most testers available were made in a time less sensitive to disabilities.

Entrope

thanks. Called Sencore up in Sioux Falls today. that was fun... all the way up till we got around to finding out they no longer supported nor made vacum tube testers. I did manage to find one resource. One I'll likely get. tests for gases, shorts, strength, and some other junk... comes with books and a 30 day warranty. Big meter. Also found an online resource for cross referencing tube types - Duncan tube data base. TDB.

Found out about it... haven't found IT yet. I will though.