I fixed a vintage amp by ignoring the schematic for once

A customer brought in a 1970s tube amp from a garage in Phoenix, and the schematic called for a specific resistor value that just wasn't working. I swapped in a slightly different value based on the actual voltage I measured at the socket, and it fired right up. Has anyone else had to go against the official docs to make something actually function?

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laura_lane6mo ago

That Phoenix heat probably cooked some components over the years. I mean, schematics are a starting point, not a bible, right? How far off was the measured voltage from what the paper said it should be?

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dylan_rodriguez6mo ago

Yeah @laura_lane, you hit it. That heat is a killer. I've seen resistors drift so bad a 5v line reads 4.2 on a good day. The paper said 12 at the regulator, but we were getting 10.8 after an hour in the sun. Schematics are a best guess from a lab in Michigan, not a car that's been in Arizona for fifteen summers.

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