Ice checked my cables and connectors and they all look ok. I’ve switched tubes and thoroughly checked solder joints. I do have a schematic and my hunch tells me that the problem is upstream of the power supply, but being a beginner, I’m starting to get into an area that requires more technical knowledge than I possess. I’m going to start going through it more methodically today but I’m doubtful that I’ll get it sorted out which is why I’m looking for a tech because I need a plan to fall back on if my efforts to solve this problem fail.
Harman Kardon A300
Hello everyone
I just did a full rebuild of this amp. Brought it up slowly with the variac and the B channel sounds great but the A channel is bad (really weak). I’ve fooled around with it now for a couple days and I’m starting to feel out of my skill set. Does anyone know of a good tech in the San Francisco Bay Area region? There used to be a couple places that were really good but audio technicians are a dying breed and hard to find. I’d be willing to deliver it anywhere in the state - don’t want to ship it since I’ve done a huge amount of aesthetic work on it and I’d hate for it to be damaged.
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@ccogopher 'upstream from the power supply' means the AC power switch and power cord, so I'm thinking you meant something else. The power supply is shared by both channels. So I think the power supply is OK. Since you have a schematic, check the voltage on the plates of the 12AX7 which is the voltage amplifier to both power amplifier channels. The plate voltage should be about 130V on pins 1 and 6. For the 12AU7 you should see about 260V on pins 1 and 6. You could also put a jumper between pins 2 and 7 of the 12AX7; this would force both channels to have the same input signal. If both channels then work, you'd know that the problem is upstream from the power amp section. You might want to read this article about restoring an A300. |
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