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So, i had just recently replaced the tubes in my DSL50. And had biased the amp myself. The procedure went smoothly, biasing each tube to 45 mV dead on. Now today, the amp faded and shut off while i was jamming.
So i took the back off, and noticed one of the pre amp tubes heaters had shut off. It came back on a few minutes later. After swapping different tubes in and out of the amp, and nohting changing, before i could even think of what was causing it i looked at one of the power tubes and saw that it was glowing quite a bit warmer than the other! So i get out my multimeter and check the bias voltage, one of the tubes is at 45 mV, right where it should be, and the other is at 160 mV and CLIMBING! So I shut off the power as quick as i could, as by that time the tube was practically a light bulb and to avoid completely killing a set of 70 dollar tubes. Now someone help me answer this, why in gods name would an amps bias shoot through the roof like that!? It is completely beyond me at this point.
Im going to keep researching, so ill update in a bit. But if anyone could provide answers or at least help, i would really appreciate it. For now ill just have to use the 50w plexi Nick Update: Just checked the bias again, the one that was normal before, is now at 82 mV.
And the other is at 42 mV. Im seriously confused.
Update 2: No real progress. I took the amp out of the chassis, and after inspecting the solder joints to the power tube sockets, well, lets say they are a bit crispy!
Update 3: Swapping in old power tubes fixed the issue. Despite that they are 12 years old. The new issue is that the preamp tube V2 is intermittently going cold. And the investigation continues!
PS I feel a change in the name of the thread from something so depressing to the current name will give me a better outlook on life. The tubes aren't even a week old, although iv read if a tube fails its either in the first week during burn in or in the long run. Ill be taking boards out tomorrow. I dont plan on seeing a repair man, only because a) its not my primary amp (my eleven rack is ) and b) I absolutly love fixing electronics.
So it should be a fun little project! Ill start testing resistors tomorrow, checking their resistances with my multimeter and comparing them to their listed resistance on the bands. Then ill be checking for expanded/swollen capacitors, burned traces, any signs of heat damage which to this point seemed to be isolated to around the socket pins. Ill keep this thread updated. The tubes aren't even a week old, although iv read if a tube fails its either in the first week during burn in or in the long run. Ill be taking boards out tomorrow.
I dont plan on seeing a repair man, only because a) its not my primary amp (my eleven rack is ) and b) I absolutly love fixing electronics. So it should be a fun little project! Ill start testing resistors tomorrow, checking their resistances with my multimeter and comparing them to their listed resistance on the bands. Then ill be checking for expanded/swollen capacitors, burned traces, any signs of heat damage which to this point seemed to be isolated to around the socket pins. Ill keep this thread updated.
Nick I would do the same thing. You have the correct schematic? I assume you can download it from Marshall. WARNING: you might have a different problem than I had with my amp, I am NO expert! Far from it actually (just so you don't get a heart attack ) I had a very similar problem sounding problem with my Ritchie Blackmore and it was BAD, very bad! The same as you I was playing my amp and I notice the tube lighting up like a light bulb, I replace tubes and the same problem.
So: trip to the technician (I'm a complete klutz ). Seems that I have massive tube failure (due to faulty sockets and whatnot) and the amp had actually burnt through the circuit in a few places. In the end I had to get complete new tubes, had the man rewire part of the circuit of the amp and was 450 $ poorer.
Now: It seems like you are quite knowledgable and able to fix this yourself so I absolutely recommend fixing it yourself! I had to pay some guy 50$/hour so if you could do it yourself, you will save yourself quite some money doing this. AGAIN: you could have a totally different problem! Fingers crossed for you that it's something ridiculous and an easy fix!!! WARNING: you might have a different problem than I had with my amp, I am NO expert! Far from it actually (just so you don't get a heart attack ) I had a very similar problem sounding problem with my Ritchie Blackmore and it was BAD, very bad!
The same as you I was playing my amp and I notice the tube lighting up like a light bulb, I replace tubes and the same problem. So: trip to the technician (I'm a complete klutz ). Seems that I have massive tube failure (due to faulty sockets and whatnot) and the amp had actually burnt through the circuit in a few places. In the end I had to get complete new tubes, had the man rewire part of the circuit of the amp and was 450 $ poorer. Now: It seems like you are quite knowledgable and able to fix this yourself so I absolutely recommend fixing it yourself!
I had to pay some guy 50$/hour so if you could do it yourself, you will save yourself quite some money doing this. AGAIN: you could have a totally different problem! Fingers crossed for you that it's something ridiculous and an easy fix!!!
So far its not looking that severe. Although it could have been because i shut mine off the second it happened.
It sounds like your could have been burning for a bit longer Thanks for the info.