Tube or Amp Problem? Please help.

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?

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.

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. 

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.

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. 

Ref: Upscale has Gold Lions for $92.95 each and Electro Harmonix for $45.95 each, no charge for matched quads.

Do you have a spare EL34? You really need to see if a tube will bias in that slot. It's possible you'll need a new resistor. Better to find out before buying a new quad and not being able to play them.

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.

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. 

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. 

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.

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.

Bigkidz thanks for the kind offer. I used to live in Brooklyn. If i still did I would definitely take you up on your offer but I know live in LA which is a bit too far!

gs5556, I was able to find some spare tubes. I put them in and was able to reduce the bias for the tube location that had the fireworks. Hopefully, that means it was just the tube and not the amp, correct?

@jkontuly if the bias pot had range when turning left and right, then the amp is ok. However, you want to make sure that bias will remain steady and not drift.

This happens with tubes sometimes that’s why we keep spares

Given that I can set the bias for each tube individually is it still important that I replace both on the side that this occurs...I still plan on doing this but just more for my own education.

Given that I can set the bias for each tube individually is it still important that I replace both on the side that this occurs

Although the bias is independent the circuit is designed to have a pair of matched tubes. 

Given that I can set the bias for each tube individually is it still important that I replace both on the side that this occurs...I still plan on doing this but just more for my own education.

Russ has given you the correct answer. And as others have said, its best to replace all of them if they have a lot of hours. FWIW you got lucky in that the tube didn't do more damage. I had a set of Shuguang Nature series in which one blew and $650 later my amp worked again. They sounded good but at a very high price. They were just getting broken in.

The Melody has a good reputation so if you like it then get some tubes. Here is some. Affordable too. Have fun

EL 34

Sorry to hear about your troubles artemus_5. Except for the current situation I haven't had any issues w/ the Shuguang Treasures and I like the sound better than the tube store preferred series that i had been using but something to keep in mind. the last thing i need is for a tube to destroy my amp. Unfortunately, i don't have unlimited funds.

Unfortunately, i don't have unlimited funds.

Not many do but tube amps take more financial commitment than solid state gear. If you want to play you have to pay.

+1  @russ69 . That's the truth.

@jkontuly  Normally I would say only replace the 2 power tubes. But if you truly have 1000 hours use, I suggest getting a quad.