[NickMimi]

Really new and still educating myself. I was warming up my amp when I noticed and heard one of my tubes make a tiny pop, which the right side speaker echoed,  and I actually saw the small spark in the middle of the tube. I quickly shut everything down, inspected the tube in question and then tried it all again. Everything seems fine but that NEVER happened before. DO i replace the tube? Is this normal? as mentioned I don't hear anything different but I was very curious. Any info is much appreciated.

[Elizabeth]

There are small bits of stuff inside tubes that can come loose and touch something with lots of voltage. The tiny fragment explodes and usually everything is fine again.
But stuff like that is why you should not leave tube amps running unattended.

I would NOT WORRY about that one event.
If it happened more and more, then think about replacing the tube. But one little event is not a problem.
There are other events which are way more problematic

[NickMimi]

Thank you very much.

[JakeJ]

Do watch the amp when you turn it on, if it happens again and it is the same tube I would replace it.

[mresseguie]

Nickmimi,

Good question! 

I'm still a tube noob. I have a follow on question:

My amp and preamp were shipped to me with matching tubes. If one fails and I replace just that one with a non-matching tube, are there consequences?

I now have a tube amp, preamp, and DAC. When one becomes microphonic, it's a pain to figure out which one is the offending tube. I love the music these components make together, but I now understand the frustration with tubes. I'm planning to buy a complete back-up set in order to have replacement tubes when the next one fails.

[FullRangeMan]

My amp and preamp were shipped to me with matching tubes. If one fails and I replace just that one with a non-matching tube, are there consequences?
Yes the tubes become unbalanced and its audible.

[RDavidson]

Side note : Unlike solid state amps, tube amps should always be connected to a load (usually speakers) when on. It's usually not a problem if all you're doing is testing a tube or two, turning it on then off shortly after. But definitely have a load connected if you plan to leave the amp on for an extended period. I'm sure someone here can explain the technical reasons for this. I believe the problem is transformer oversaturation. The consequence of that is tubes eventually blowing up. Just a tip for tube newbs.

[mresseguie]

My amp and preamp were shipped to me with matching tubes. If one fails and I replace just that one with a non-matching tube, are there consequences?
Yes the tubes become unbalanced and its audible.

Hmm. This suggests that I must replace all four 6SN7 or all four KT88 tubes rather than just the single failing tube. I can reuse the three remaining 6SN7 tubes in my Kootenay 120 amp, but three still good KT88 tubes.....are destined for a box or a sale, it seems. Or can I try to buy a matching tube to make a complete set again?

Good info here! Thank you!

Michael

[dB Cooper]

Nickmimi,

Good question! 


I now have a tube amp, preamp, and DAC. When one becomes microphonic, it's a pain to figure out which one is the offending tube.

Not difficult. Only pain (unless you are careless and make your body a path to ground) is taking the cover off to gain access to the tubes (unnecessary if the equipment has one of those 'Look, I've got tubes' covers where the tubes poke through). Tap the tubes (gently!) with the eraser end of a pencil to find the offender.

If a tube is microphonic, it is either old or was defective to begin with. If a tube ever sparked in any of my equipment (no glass these days), it would be gone faster than you can say Jack Robinson.

[ArthurDent]

Michael - I think you'd want to replace them in "sets", per channel. The good one(s) from the 'old' set save for future emergency use. No need to change all of them. Usually the boxes for the tubes will have the testing info on them so you can simply try to match as close to each other when substituting the 'old' tubes in if you have another failure. Not an expert, but have swapped emails with Frank VA on some past issues I've had. That's the impression I got, unless you've got loads of $.

JD

[bacobits1]

I have KT120's here, individual biasing and fused, soft start. If a power tube is not holding bias it gets replaced. Check every 6 months or so. They may not "glow" the same either.
Naturally if it's red plating get it otta there a fuse will blow. Fuses are there so other parts will not be taken out if something happens. I would replace just the one tube, but buy a pair. I think it's important to buy tested, burned in KT120's to clear all this when installing new tubes. Small signal tubes last for some time (years) if the piece designed correctly.

Oh, popping or noise of any kind replace it. I have a NOS Tungram 12AU7 here from Upscale Audio. It flairs up at the bottom on startup no noise. This tube is known to do that (normal). I have another one and it does not do that.

Tube amps are like firing up a boiler..............

[leftside]

A lot of modern tube amps will have absolutely no problem with unmatched tubes, so you'll only need to replace one of those expensive KT88's if one fails.

[mresseguie]

A lot of modern tube amps will have absolutely no problem with unmatched tubes, so you'll only need to replace one of those expensive KT88's if one fails.

Nice to know! I'll double check with Don just to be safe.

I'm going to buy a backup set of Shuguang WE 6SN7 tubes - just because...

[A_shah]

 I . Had a tube go microphonic in the DS 2  pre .  Asked Don, he told me  that I  just replace the bad tube I just went ahead and ordered a  pair from Don and replaced them , I  tend  to agree with @FullRangeman , &  @leftside with regards to modern tubes just check how closely they are matched with the numbers given on the tube , I have been very lucky to live close by to Mike Sanders of QuickSilver audio I am just amazed to see his  engineering skills & circuit designs of pure tube  amps without circuits boards , unlike other  one man operations he has a full work shop with people working  for him  in an industrial area and I  was lucky to visit him at his lab house ! ( he owns two homes in a gated community ) Lab house also house's a huge set of Horn speakers size of a VWBug each -he got those from a cinema hall with 4 huge woofers in each ! occupying the whole living room , I was wondering how he got those inside the house ? MIKE  was able to drive those 106 db speakers with his 3.5 watt/7 volt Headphone amp !! most of  his amps seems to be going to Asia , anyway he is  also of the view that  tubes should be matched and "burnt "before being installed in a amplifier unless NOS tubes he does NOT  like expensive tubes  , Hope this helps 

Asghar