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got another x100b on my bench this week. i fixed one recently for a friend, so when i talked to another guy who was complaining of similar symptoms with his newly acquired carvin i figured i knew exactly what to do.
he says he was playing the amp and it suddenly just cut out. i opened it up and found R121 loose in the chassis. i've seen this before, so i installed a new 10w 350 ohm @ R121 and i swapped out the screen resistors for 1k5w.
i tested the power tubes and while i didn't find any shorts i DID find one of the tubes failed the grid leakage test. this being a recent ebay purchase, i figured new power tubes were the safest way to proceed.
before i installed new tubes and an adjustable bias i tried to listen to where the amp was at with some used known good tubes. not a sound came out the speaker.
i plugged a 9v powered amp into the effects SEND... nothing.
i used a signal probe to trace the input source through the gain stages and the sound makes it out of V1 but not out of V2.
around this time R133 (22ohm at the rectifier) started smoking and that's when i turned the amp off.
any thoughts as to what would cause R133 to heat up so quickly? would a bad op-amp draw too much current? i never put the pre tubes on my tester... perhaps there's an issue there?
it's too late for me to poke around any more tonight, but i wanted to start this conversation asap to see where everyone's mind goes to to give me some ideas.
he says he was playing the amp and it suddenly just cut out. i opened it up and found R121 loose in the chassis. i've seen this before, so i installed a new 10w 350 ohm @ R121 and i swapped out the screen resistors for 1k5w.
i tested the power tubes and while i didn't find any shorts i DID find one of the tubes failed the grid leakage test. this being a recent ebay purchase, i figured new power tubes were the safest way to proceed.
before i installed new tubes and an adjustable bias i tried to listen to where the amp was at with some used known good tubes. not a sound came out the speaker.
i plugged a 9v powered amp into the effects SEND... nothing.
i used a signal probe to trace the input source through the gain stages and the sound makes it out of V1 but not out of V2.
around this time R133 (22ohm at the rectifier) started smoking and that's when i turned the amp off.
any thoughts as to what would cause R133 to heat up so quickly? would a bad op-amp draw too much current? i never put the pre tubes on my tester... perhaps there's an issue there?
it's too late for me to poke around any more tonight, but i wanted to start this conversation asap to see where everyone's mind goes to to give me some ideas.
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