2. amps-preamps
  3. 177110-5705

Tube or Amp Problem? Please help.

I have a Melody El34 Integrated Amp that I use with 2 pairs of Shuguang Treasure 6CA7-z. Last week I was listening to music when everything went all horrible sounding and one of the tubes lit up like blue fireworks. I turned off the amp and looked at it the next day. To my, admittedly untrained eye, the tube looks fine but when I checked the bias it was at .32 (the amp says to set to .40) so I tried to set it to .40 but it would only go to .34. All of the other tubes I can set to .40. I have never had this issue with this amp. Is it the tube or did something happen to the amp? If it's just the tube will it be ok to have one set to .34 and the other .4 or should I set both tubes to .34, all 4? I would buy a new pair but they were expensive and on top of that don't seem to be offered anymore.

128x128jkontuly
jkontuly's avatar
jkontuly OP
59 posts
 

lowrider57, I am not home now but I will check. If I do I will definitely try it out. Hope I do but unfortunately I don't think so.

russ69, thanks for all of your helpful comments.

oddiofyl's avatar
oddiofyl
3,834 posts
 

I agree.   Try a different tube.  Tubes that do that have an internal short or something that made it have a fireworks display.  
 

hopefully a new tube on that position will bias fine and sound will return as normal. 

ghdprentice
6,969 posts
 

Good advice above. If peak performance is what you are after then replace both sides. I would recommend ordering two complete sets. I always have a spare set.  While not tremendously unreliable… tubes wear out and occasionally fail. With a thousand hours on them, I would (me) swap them all out. Tubes are getting more expensive… as a hedge, having an extra set doesn’t hurt. 

bigkidz
3,381 posts
 

Tube is probably bad and the bias from the resistors is probably also gone bad.  Check under the hood to see if you see any burn marks on any part, and have the tube tested.  

 

If you are close to New Jersey, I would help you take a look and evaluate the issue.

Happy Listening.

 

gs5556
1,234 posts
 

Without cross checking with other tubes, I wouldn't run the amplifier. There may be a problem with the screen voltage being out of spec (which can cause tube failure, distortion, and/or inability to increase or decrease plate current to spec). The amp will probably continue to eat tubes on that socket. 

A lot of times it is bad solder joints that causes these kinds of problems after a good amount of time of normal operation -- and simply reflowing solder joints solves the problem.

 

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