how do you know a bad tube?

I'm thinking of winding up all or at least mostly with tube gear. that said, how does a person know for sure which tube device needs a tube?

By that i mean, if you have multiple preamps, and amps, then I'd see it as not a lot of trouble determineing which one has perhaps an issue. but if you only have one pre and one amp both with tubes and things begin to sound funky, how then do you tell which unit is the culprit?

Past that then, how do you know which tube? (given there aren't any indicators on the chasis, and the tube itself isn't dead blown). ?? ...and apart from having on hand dupes of all the tubes in the system.

I am overlooking the obvious here for a reason. I'd as soon not have to get a tube tester. Unless there is a mighty simple one to use which has an oscillator in it as well as meters.

Sorry if it is a dumb question, but sure seems like a simple answer here will come in handy later on... as I'm looking for an "in house" solution that ain't way expensive and is simple enough tactilly for me to use.

thanks much
The simplest way is by simply switching tubes from left to right channel and vis a versa using a process of elimination. For example you have four tubes in a pre-amp. You move the two on the left to the right side and the reverse. Nothing changes. Likely then that isn't your problem. Then you move on to the next component (amp) and do the same thing. Let say the problem changes channels. Now you move one of those potentially bad tubes back into the other channel in exchange for a known good tube - if the problem moves that is the bad tube. If it doesn't move the one you didn't pull is a problem.

Different problem, different solution, but that is the easiest way to isolate a bad tube for newbies. You don't need a tester, just ears and a little logic.
Depending on what kind of tube failure you are experiencing, you can sometimes get a good idea by simply looking at the tubes closely.
Well I sort of got that bit all by my lonesome, but it's good you pointed it out. ...and if you have but one tube and no twin? (several tubes, two singles, different types: and one type is pairs)??

Thanks. perhaps you missed my handle, and refference to an oscilator (audible indicator), but thanks anyway. Although, unless one is familiar with the tube archetecture beforehand, past the obvious, what could one hope to glean?
Maybe I missed your point.

if there are same/same tubes on either channel, certinaly one can swap back and forth. Sure, if a tube won't light up.. yep, it's dead. There are tube components that do not duplicate the tubes within it throughout its design.

Then what?

In that case there is no other tube present to swap about within the unit. That scenario happens to be the case in an upcoming unit for me, so I thought it may well be also the way with the possible amp (s), therefore I thought to avail myself of some greater experience, or unbeknownest to me, device or method, before the fact.

it would seem at this point only having exact same spares or a tester, is the ticket... and/or at least an inexpensive integrated with pre outs and main ins, or a couple of real budget pre & amp pieces about just in case.
when I owned the VK5i I found switching tubes side to side could usually isolate or even make go away the problems I was having with other posters said, if the problem switches to the other channel then you have identified the culprit.
You should have at least one extra set of tubes. That extra set will provide the tubes to swap and test for the bad unit. It also means your equipment is never out of commission just because a tube is going bad.
Got it. Thanks. i never did notice much of a diff in the VK5i, from swapping from side to side... as the thing biases itself each time... but then I must never have had a severely poor tube. the biggest/best thing in that unit I found was having all the same tubes in the signal path, and play with something in the shunts. ultimately, i found that the simplest and best way to outfit the unit.

it sure does seem the way. Another set entirely. Geezzz Louise.

See I was thinking there is some really neat gizmo out there that one can plug a tube into for just strength or short testing. Like a wiggins voltmeter.... and I'd not have to spend hundreds for a tester i probably cant read well enough anyways... and need to periodically recalibrate.

Oil well. Thanks. Thanks very much... of course if there is someone out there who knows of a simple tester which does a good job is sturdy, with B-I-G meters, and seldom requires calibration...I would like to hear about it, and where it is available.

A couple of the tube amps I am thinking about have quite a number of tubes in them... and some singles in there as well... an affordable tester I could use does seem relevant to have if you're going to pursue an all tube system, doesn't it?.
Tube tester.
Blindjim. I think others have addressed your tube dilema very well. I`m curious, after reading your "what would your next upgrade be" thread on your system page, what your impression of Herbies tweaks is and how you`re doing with the room tuning.

I`m a big "Herbies" fan and have implemented (one at a time) every dampening tweak that Steve offers. Each implimentation isolated instruments more and more and brought a more realistic soundstage. I`m very happy with the results.

I`m also doing some room tuning and am curious as to how you`re coming along with yours. Maybe you could update your other thread (if you feel like it). It was an interesting read for me, and I assume, others.
I don't know of any kind of simple and cheap tube tester that will reliably tell you when a tube is going bad. Most testers are not cheap and many require calibration and maintenance.

Also, a tube can begin to go bad in ways that certain testers will not be able to detect. Even a good tester that measures transconductance, may give you an idea of the strength of the tube, but not other conditions, such as noise. I had a small signal tube, an EH 6sn7, that became gassy. It tests spectacularly strong for transconductance, but my tester (not cheap) also tests for gassy condition and it showed that this tube was horrible in that respect.
i apologize for not promptly or even regularly giving some followup there. i will.

yeah. i was just hoping aginnst hope, I had overlooked something easy, or some other fashion or method going forward to check things out. if I do wind up with a pair of tube mono blocks as well, and something goes awry, I'll have a coniption fit trying to swap in and out tubes from a second set as was mentioned previously... but is a good idea. one I have followed in the past. one also that is a mite pricey. As I chose then to get them all from reputable dealers and none have actually gone bad on me Save the first set i got which came with the preamp, but were disposed of shortly thereafter. man. if there is anything I hate to do it's trash a tube that still lights up, and it is tiresome and expensive to send them out to have checked. Not to mention the waiting period (s).

OK. A second set instead of a tester. Super.

Does anyone make one tube monos?
What is cheap for a tube tester compared to a second set of tubes at today's spiraling prices or damaging a component with a bad tube?

I found a Sencore Mity Mite VII for $100 without looking to hard. But even at $200 or $300 if you have a long term commitment to tube gear then it makes sense to have one.
they won't look you in the eye.


yes, $100 - $300 is cheap. I'd have no issues going for something like that. My concerns, are it's use. meter/display size, and calibration needs... doing twin triodes, large power tubes, in all, it's flexibility and naturally it's accuracy.

meters/displays need be of substantioal size for me. Figuring it out is not much of a problem there after. although I appear dumb as a stump sometimes, i don't believe I really am.

Waht resource sells these things?
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. :-)

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.

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.


"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.

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:

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.

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.
Try this for tube cross reference online:

thanks, I will.