I have a turret board build of an Eqp-1a that I built years ago that has developed intermittent noise.
Here is a recording I made of the noise:
https://www.dropbox.com/scl/fi/z6ir...oise.mp3?rlkey=v1wjo6pbg4441w0koj94wd2k5&dl=0
I tried swapping tubes, and after going through a few a found a pair that had no noise at all, but the next time I turned the unit on the noise was back. I suspected it might be the cathode resistors, and tried gently poking around with a wooden skewer. I discovered that the 0.25mf caps that go from the cathodes of V1 to the grids of V2, as well as the 50uf capacitors that go from B+ to the cathodes of V2 all audibly respond to tapping. Could it be that all 4 capacitors are microphonic? How useful is this as a diagnostic tool?
Thanks for any suggestions!
Here is a recording I made of the noise:
https://www.dropbox.com/scl/fi/z6ir...oise.mp3?rlkey=v1wjo6pbg4441w0koj94wd2k5&dl=0
I tried swapping tubes, and after going through a few a found a pair that had no noise at all, but the next time I turned the unit on the noise was back. I suspected it might be the cathode resistors, and tried gently poking around with a wooden skewer. I discovered that the 0.25mf caps that go from the cathodes of V1 to the grids of V2, as well as the 50uf capacitors that go from B+ to the cathodes of V2 all audibly respond to tapping. Could it be that all 4 capacitors are microphonic? How useful is this as a diagnostic tool?
Thanks for any suggestions!