Recent content by dbdb

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    Yamaha CA 800 right channel noise

    Finally ordered those transistors! And an Atlas dca 55. New parts are in and bias/current/rail v is super stable. Thanks a bunch!
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    Yamaha CA 800 right channel noise

    So, six months later and I finally feel like I have time to finish this project. About to order a bunch of stuff. This tool in the link (quoted) doesn’t specifically say that it measures Hfe (or maybe it does and I don’t know enough to know better). Also, these transistors...
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    Yamaha CA 800 right channel noise

    I have a Sperry dm-6400
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    Yamaha CA 800 right channel noise

    I’m hesitant to call it good. It takes a full hour to go from .35v ish to .01v ish, and will still jump up and down +\- 20mv when it’s finally fully warmed up. If I blow on the right channel to cool it after a full warm up, it will swing back up like 50mv and take a couple minutes to get back...
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    Yamaha CA 800 right channel noise

    Wow. How would you test them? To what tolerance? Are those two components directly responsible for balancing dc offset? Definitely never noticed any pops in the speakers... Honestly, the amp sounds really good over all. Especially after a good hour of warm up time. I’m only having a little white...
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    Yamaha CA 800 right channel noise

    Also, I’m assuming I’ll have to pay the 8 bucks for shipping for a 22 cent part, so while I’m at it I’d like to compile a full list of caps and other parts worth replacing. Kinda wanna go more in a restoration direction with it. Any specific brands or recommendations for components? I.e uf...
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    Yamaha CA 800 right channel noise

    Is that link a pair of those transistors? They’re sold in pairs?
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    Yamaha CA 800 right channel noise

    The buzz coming from the transformer is so quiet it was probably not worth mentioning. Had to almost stick my ear on it to notice
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    Yamaha CA 800 right channel noise

    Yes. Speakers disconnected and pre amp decoupled. Turned the volume down all the way even though that wouldn’t make a difference with the preamp decoupled. Nothing plugged into the receiver
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    Yamaha CA 800 right channel noise

    Since the power supply is common to both channels, wouldn’t the left channel show some of the same issues if there’s a problem in the power supply? Left channel is in perfect working order. Goes almost immediately and almost exactly to spec in bias, dc offset and idle current with less than...
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    Yamaha CA 800 right channel noise

    So after work today I hooked up the multi meter to check dc offset in the right channel from a completely cold start. I had balanced it well within spec the night before, but when I turned it on the damn thing started at -0.3v and after about 5-6 min of warm up eventually got to -0.16v. At that...
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    Yamaha CA 800 right channel noise

    Okay. So maybe transistor 2sc458lg is the cause of the fluctuation in the dc offset? Probably other things could be suspect as well... does it make sense that bad caps are responsible for the long amount of time needed to get the offset to spec, and even then will still jump up and down a bunch...
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    Yamaha CA 800 right channel noise

    So more specifically, the right channel takes almost three minutes to go from -0.08v to -0.006 ish (within spec on step b) after I turn it on. And from there it jumps around +/- 0.01v, where as the left channel goes right to 0.000 within a few seconds. Sup with that??? I’m obviously lacking...
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    Yamaha CA 800 right channel noise

    Thanks for the tips. Would those 2sc458LG transistors maybe be the next culprit in line for getting rid of the bit of floor noise that’s still present in the right channel? And are the multiturn trimmers a replacement for the pots on 601,602,603,604? Maybe that’s where some of that noise is...
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    Yamaha CA 800 right channel noise

    Success. Working order again. Got the bias and voltage set well within spec. Also used a temp gun to be sure the thermal compound was doing its job. Both channels transistors are fully warmed up and at 131 degrees F, and the heat sinks read 130. I’d say that compound is working pretty damn well...
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