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
blackdoghifi's avatar
blackdoghifi
45 posts
 

If it lit up like "blue fireworks" that tube is probably fried. I would not be using it.

There's also a possibility that a resistor is burnt as well in the amp, but since you can get some bias, that isn't likely.

Take one of your other tubes and try it in the socket where the tube failed. Does it bias?

 

 

jkontuly's avatar
jkontuly OP
59 posts
 

Thanks blackdog. I don't have extra tubes right now would it be safe to switch the tubes on the same side just to test and see if can get the bias to .4? Just don't want to fry another tube. Unfortunately, it seems like these tubes aren't for sale anymore and ones that are seem to have shot up in price over the past 2 years.

 

russ69's avatar
russ69
3,518 posts
 

Next time when you see fireworks (or the sound changes), shut the amp off immediately. That tube is blown. If you have a lot of hours on that set of tubes, it’s an indication that the other tubes may not be that far behind. If that is the case, it’s time for a new set of tubes. Turn down your bias before you install the new tubes. Warm up for a good half hour and then bias the tubes.

On most 2 tubes per channel amps with manual bias, you want to have matching tubes for the pair. They are designed to run that way and it will be hard on other components if they don't match. Some newer, automatic bias amps will let you run any tube but that is not the way most amps are. 

jkontuly's avatar
jkontuly OP
59 posts
 

Thanks russ69. I don't have that many hours on the tubes, had them for maybe 2 years but only probably use 5-10 hours of week due to busy schedule. if I keep the 2 shuguang treasures on 1 side will it sound bad if I replace the 2 on the side w/ the bad tube with something else? As I mentioned don't think I can find these tubes now and even if I could they are very pricey.

russ69's avatar
russ69
3,518 posts
 

will it sound bad if I replace the 2 on the side w/ the bad tube with something else? 

Probably not but it might sound different on each side. I saw on the web that those tubes might not be very robust and you have around 1000 hours on them. You can change just a pair but if it was me I'd get a matched quad and start fresh. When you bring the bias to spec and everything adjusts normally, chances are the amp is fine. 

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