Milky Imploded EL34

[Chargin265]

One of my El34 Svetlana 9631 valves has sucked itself to death. Is this normal failure or does it indicate there could be other issues. I intend replacing all tubes with matching sets. Is this type of valve failure normal or is it time for an expert to give my amp the once over? The amp is a 1997 Anniversary 100 Watt Superlead.

 

[Roadburn]

It is hard to tell. Tubes are not predictable (lifespan etc.) and can fail after 1 minute of operation, but they could also last you a couple of years.

I would get it re-tubed by a specialist (2 slightly missmatched pairs, within tolerance of the amp ofcourse).
If there is somethig wrong with the amp, it will probably turn up.

 

[Ken]

Sounds like a typical vacuum leak. The tube was damaged or defective; I'm not aware of any electrical failure that could cause a vacuum leak but some of the actual techs here might chime in on that.

I would replace the tubes and not spend tech money unless it happens again.

Ken

 

[Marshall Mann]

Nothing electrical will cause a tube to lose vacuum. It's a physical failure, and is fairly normal. The stress of heating and cooling over years of use will bring out any small imperfections in the glass.

Unless you suspect something different, it's best to just re-tube the head and see how it does.

 

[Chargin265]

I have a quad of matched tubes ready to install tonight. Thank you for the advice.

 

[Roadburn]

I have a quad of matched tubes ready to install tonight. Thank you for the advice.

It's personal preference, but why a matched quad?

You have a vintage style amp, which loves powertube saturation.
Matched pairs/quads are nice, but have less harmonics then slightly missmatched sets...

 

[big dooley]

It's personal preference, but why a matched quad?

You have a vintage style amp, which loves powertube saturation.
Matched pairs/quads are nice, but have less harmonics then slightly missmatched sets...

these days quite some people get "matched quads" with a bloody 10mA difference between tubes... put them in a vintage style amp with only one biastrimpot, using a single probe and chances are that people pick the coldest running tube, set the bias for that tube at 65% while the hottest running tube is set at near selfdestruction

a quad of tubes will always have a slight mismatch, but running a good matched pair or quad is just a cheap insurance.... if i want more even order harmonics by an imbalanced poweramp, i'd rather put a 12DW7 in the PI

 

[Roadburn]

Ahhhh.
I thought a 100Watter would have a seperate biastrimpot for each pair by default.

 

[Chargin265]

I must admit I put in a matched quad because I thought that was the correct way to go about it.

 

[Roadburn]

these days quite some people get "matched quads" with a bloody 10mA difference between tubes... put them in a vintage style amp with only one biastrimpot, using a single probe and chances are that people pick the coldest running tube, set the bias for that tube at 65% while the hottest running tube is set at near selfdestruction

a quad of tubes will always have a slight mismatch, but running a good matched pair or quad is just a cheap insurance.... if i want more even order harmonics by an imbalanced poweramp, i'd rather put a 12DW7 in the PI

I must admit I put in a matched quad because I thought that was the correct way to go about it.

Appearantly it is the way to go. Good call!

 

[big dooley]

Ahhhh.
I thought a 100Watter would have a seperate biastrimpot for each pair by default.

these days most amps have at least dual trimpots from the JCM2000's onwards and mostly all the reissues have twin trimpots as well now

when marshall goes on with their autobias system, it'll become a lot easier for end users... i've monitored the bias on my AFD100, when it did it's thing, and no matter what you put in there, as long as the tube is functioning properly, it'll be set at the cathodecurrent you dialed in on the back

 

[Marshall Mann]

I must admit I put in a matched quad because I thought that was the correct way to go about it.

It is.