Tweet
i've got a triple rec here (3 channel), i can't find a schematic for it online, but i've got it up and running currently and i have some questions.
so...i received the amp w/ a blown fuse and the owner said that channel 1 and 3 were low volume, but channel 2 seemed strong...the last time he fired it up it blew a fuse. then it came to me. he was on tour w/ it recently and took it to a tech on the road who claimed that some of the tubes were getting a little weak but the tech was able to play the amp at volume for an hour or two w/ no issues. his final diagnosis was that the tubes should be replaced after tour.
fast forward to it being on my bench....
first 3 pre-tubes test w/ one strong triode and one weak triode each. they also came to me in the amp w/ the word, "BAD" written on them.
i will be replacing those.
2 out of 3 rectifier tubes don't test at all, filaments don't even light. one had something loose rattling around in it, i suspect that's the cause for blown fuse. in any case, owner always operates the amp in diode-rectified mode. so i've simply pulled the rectifier tubes for the rest of the testing.
now that the back story is caught up, i've got the amp working with seemingly typical output power. i've pulled all rectifier tubes, tested all tubes throughout the amp and it's currently working w/ pre- and power- tubes that it came to me with. however there is a low frequency oscillation after the amp receives a signal that sounds like a truck driving down the road. oscillation goes away w/ PI pulled. the oscillation won't start until a few seconds after you run a signal into the amp. sitting on and unused, it's quiet. i can't find any obvious loose connections w/ a chopstick, and i don't have a schematic...so i'm unsure where to go from here. suggestions?
so...i received the amp w/ a blown fuse and the owner said that channel 1 and 3 were low volume, but channel 2 seemed strong...the last time he fired it up it blew a fuse. then it came to me. he was on tour w/ it recently and took it to a tech on the road who claimed that some of the tubes were getting a little weak but the tech was able to play the amp at volume for an hour or two w/ no issues. his final diagnosis was that the tubes should be replaced after tour.
fast forward to it being on my bench....
first 3 pre-tubes test w/ one strong triode and one weak triode each. they also came to me in the amp w/ the word, "BAD" written on them.
i will be replacing those.2 out of 3 rectifier tubes don't test at all, filaments don't even light. one had something loose rattling around in it, i suspect that's the cause for blown fuse. in any case, owner always operates the amp in diode-rectified mode. so i've simply pulled the rectifier tubes for the rest of the testing.
now that the back story is caught up, i've got the amp working with seemingly typical output power. i've pulled all rectifier tubes, tested all tubes throughout the amp and it's currently working w/ pre- and power- tubes that it came to me with. however there is a low frequency oscillation after the amp receives a signal that sounds like a truck driving down the road. oscillation goes away w/ PI pulled. the oscillation won't start until a few seconds after you run a signal into the amp. sitting on and unused, it's quiet. i can't find any obvious loose connections w/ a chopstick, and i don't have a schematic...so i'm unsure where to go from here. suggestions?
Comment