[breakfastchef]

I had a 12AU7 go bad on me. What caused this tube to fail? The bad tube (on the left, of course) looks like a snow globe inside. What is the material on the inside top of the tube anyway? I am taking a guess that air intrusion was the culprit.

 

[takezo]

yes, it's caused by a failed vacuum seal... a crack in the glass or
more likely a seal break along the pins and glass envelope... the
silver patch on top is barium, most likely, which oxidizes very easily
in the presence of oxygen to produce the white powdery substance
called barium oxide.

 

[intoart]

The more I learn about tubes from the point of view of maintenance, the less inclined I am to want a tube amp (in spite of the fact that they are said to sound great.) I think I would be better off with a really good SS amp. Top contender at this point is the Little Dot MKV (I had previously considered the MKIV instead.)

 

[nor_spoon]

Quote:

Originally Posted by intoart /img/forum/go_quote.gif The more I learn about tubes from the point of view of maintenance, the less inclined I am to want a tube amp (in spite of the fact that they are said to sound great.) I think I would be better off with a really good SS amp. Top contender at this point is the Little Dot MKV (I had previously considered the MKIV instead.)

You will miss a lot of fun...

Transistors fail too, just as tubes do sometimes.

 

[atbglenn]

Quote:

Originally Posted by intoart /img/forum/go_quote.gif The more I learn about tubes from the point of view of maintenance, the less inclined I am to want a tube amp (in spite of the fact that they are said to sound great.) I think I would be better off with a really good SS amp. Top contender at this point is the Little Dot MKV (I had previously considered the MKIV instead.)

It's much harder to troubleshoot SS than tubes. The LD MK5 Is very complicated internally. Try fixing it if it fails. Unless you are an experienced technician, forget it.
I've had tube amps last for years before tube replacements were necessary. Yes, tubes do fail at times, but are easily replaced.

 

[Nick 214]

Quote:

Originally Posted by atbglenn /img/forum/go_quote.gif It's much harder to troubleshoot SS than tubes. The LD MK5 Is very complicated internally. Try fixing it if it fails. Unless you are an experienced technician, forget it. I've had tube amps last for years before tube replacements were necessary. Yes, tubes do fail at times, but are easily replaced.

Very good point. Also, many tubes have lots of substitutes, and can be switched to entirely other tubes with just a few circuit mods. To change the output devices in many SS amps, you'll have to do a lot of work, especially if the devices are OOP.

 

[intoart]

Well, OK. I guess I am convinced.
Since the LD Mark IV is no longer available on ebay, and since I don't trust Audiophilechina to sell me a true 110 volt version (after another thread I read about them and the DV Figaro), I may have to stick to the Mark III.

I look forward to my next paycheck when I can afford to try it. What excites me the most is the promise of a truly huge soundstage.

 

[atbglenn]

Check out David on ebay. He's probably the most reliable authorized overseas dealer.
Little Dot MK III Headphone Tube Amplifier/Pre-Amp - eBay (item 190278183503 end time Feb-03-09 13:00:42 PST)

 

[tintin47]

You can just ask the seller, David, to put up a new Mk IV for sale on ebay. Or you can just go through the little dot website, little-tube.com. If you send David a message there you can just use paypal.