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After many delays, I've built myself a guitar amp from an old Heathkit A7-E. It sounds like a guitar amp! My first success--but a limited one.
A couple problems:
1. the predictable one is hum. Pretty loud, at all volumes. I grounded (I think) as per Loudthud's suggestions, using a buss that terminates to the chassis down at the input end of things. Every circuit/component grounds to the buss in the order shown on the schematic, except the 3rd wire from the power cord, which grounds to chassis at the other end, at a PT bolt. Anyone want to offer a list of the top places to suspect for the hum source?
2. The entire chassis and every tube on it seems to be microphonic, increasing as the volume is turned up. Tapping any part of the chassis or any tube rings loud through the speaker. Can one microphonic tube really pick up the vibrations from the whole amp like this? How do I test for the source?
A couple problems:
1. the predictable one is hum. Pretty loud, at all volumes. I grounded (I think) as per Loudthud's suggestions, using a buss that terminates to the chassis down at the input end of things. Every circuit/component grounds to the buss in the order shown on the schematic, except the 3rd wire from the power cord, which grounds to chassis at the other end, at a PT bolt. Anyone want to offer a list of the top places to suspect for the hum source?
2. The entire chassis and every tube on it seems to be microphonic, increasing as the volume is turned up. Tapping any part of the chassis or any tube rings loud through the speaker. Can one microphonic tube really pick up the vibrations from the whole amp like this? How do I test for the source?
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