[McPanse]

How can you tell when a tube is going bad?

I'd been noticing that my Little Dot MKIV had been making tiny little tube noises even after it was warmed up. These were little 'tings' that sounded to me ear like the glass and/or metal components inside expanding or contracting.

Fast forward to this evening: I power on the Little Dot, let it warm up a few minutes and turn on my Trends amp, which I use to drive my speakers. Big bursts of static. I turn off the Trends and let the LD warm up a bit more. Turn back on the Trends and no problem. Several minutes later --maybe 10, I can't be sure -- my right channel goes completely distorted; no music -- just lots of pops and grumbles.

I power everything down and notice smoke coming out from beneath the Little Dot.

Would a spent tube cause something like this to happen?

I tried to remove the LD's case to see if there is any visible burn damage, but I could only get the pack panel off. No easy way that I could see to expose the circuit panel.

David at Little Dot says to send it on back and I certainly intend to.

Can anybody tells me how tubes behave when they go bad? How do you know a tube has given up the ghost? (the tubes in question seem a little blacker up top than I recall).

 

[XXII]

It could be a tube problem. Can't you just swap left and right tubes to see if the distortion swaps to the other channel?

Edit: I just noticed the part about smoke. Then it's probably not a tube problem and something has fried up inside. You should send it back to LD.

 

[Uncle Erik]

When Tubes Go Bad! That would make an awesome reality TV show.

It could be a tube, but it sounds like something cooked off inside your amp. Tubes don't smoke when they die unless something really catastrophic happens. You'd know it if it did. A dead tube doesn't usually kill components, but dead components often kill tubes. I'd send it back for warranty work.

Also, the tinkling sounds are completely normal. That's the metal and glass expanding during warmup.

 

[Hrama]

Actually, I'm quite glad you made this thread McPanse as I have a question myself if a problem like the one I have is tube related. Alright, so my LDMKIII is great and such, had it for a while now and it has sounded wonderful, until just recently. I use a pair of HD-650s with them and bass has always been nice and tight even at fairly ludicrous volumes but suddenly, especially in the left channel, bass has started to become distorted even at lower volumes. It just ruins everything completely, distorting the mids and highs as well when those delicious low tones hit. Checked out my headphones on my Yamaha amp and it's definitely not them, they sound incredible as usual. Switched the positions of both sets of tubes on the Little Dot and it has not had any effect. I really hope it's not the amp itself and it's just a bad power tube or something. Anyone have any thoughts as to the cause?

 

[aryntha]

Unfortunately if the distortion doesn't follow the tube positions, its probably not the tubes.

Maybe a bad cap... Would like to hear what comes of it though as I have a MKIII as well...

 

[Hrama]

Well, after a couple more hours of critical listening, with a more discerning source, I can confirm the distortion effects both channels equally. Switching the input channels also yields the same results: Distorted, flabby bass at both low-medium and higher listening levels. Now it really does concern me that it is not simply a tube going bad. Whew, it's even making my Yamaha amp start to sound good in comparison, which is a scary thing.