Saggy
New member
Hi tone bros, I'm in need of some help as I have a sick amp and often turn here in times of trouble.
A few weeks ago at band practice, my amplifier was working fine with EL34s. When someone sabotaged it and put it on 6L6 mode, the next time I played it, it began motorboating or "putt-putting," and shortly thereafter, as I was figuring out there was a problem, the fuse blew. When this happened, the jewel light would not even come on. After properly biasing it, and replacing the fuse, the light came on again, but still it was motorboating.
I've just replaced all the tubes with brand new 6L6s and 12AX7s, and it's still doing it. The clean channel sounds distorted and the distortion channel is perfect for playing the intro to, "Welcome to the Machine." :eek1:
There are a couple of issues of concern. 1) when trying to replace the power tubes, both of their plastic center plugs broke off inside the amp, but they have since been cleared out of the hole and power tubes fit fine. What I'm more concerned about, though, are the 2) gain stages for the preamp. I ordered 4 of a standard 12AX7 tube, then one "special" 12AX7A for the "critical gain stage one" which I assumed was on the leftmost side of the preamp tubes, so I put that one there. Since we're just talking preamp tubes, I doubt this is the problem, but since it sounds distorted it could be a wrong preamp tube in the "gain" stage maybe?
Can anyone help me diagnose and solve the problem, saving me hundreds of dollars and invaluable time by not having to hire a tech? I would appreciate any helpful comments, advice, or suggestions. Thanks!
A few weeks ago at band practice, my amplifier was working fine with EL34s. When someone sabotaged it and put it on 6L6 mode, the next time I played it, it began motorboating or "putt-putting," and shortly thereafter, as I was figuring out there was a problem, the fuse blew. When this happened, the jewel light would not even come on. After properly biasing it, and replacing the fuse, the light came on again, but still it was motorboating.
I've just replaced all the tubes with brand new 6L6s and 12AX7s, and it's still doing it. The clean channel sounds distorted and the distortion channel is perfect for playing the intro to, "Welcome to the Machine." :eek1:
There are a couple of issues of concern. 1) when trying to replace the power tubes, both of their plastic center plugs broke off inside the amp, but they have since been cleared out of the hole and power tubes fit fine. What I'm more concerned about, though, are the 2) gain stages for the preamp. I ordered 4 of a standard 12AX7 tube, then one "special" 12AX7A for the "critical gain stage one" which I assumed was on the leftmost side of the preamp tubes, so I put that one there. Since we're just talking preamp tubes, I doubt this is the problem, but since it sounds distorted it could be a wrong preamp tube in the "gain" stage maybe?
Can anyone help me diagnose and solve the problem, saving me hundreds of dollars and invaluable time by not having to hire a tech? I would appreciate any helpful comments, advice, or suggestions. Thanks!