[Here come da goat]

I’ve a 1970 GTO, 400 non RA, bone stock.
Recently replaced battery, alternator and voltage regulator.
No perceived issue charging, but there is a hum (squeak) from VR at idle and low RPM. At roughly 1,100 RPM it goes away.
When at idle (and while the hum is there) I am getting ~13.8 volts out of system, at RPM above 1,100 the hum goes away but voltage then drops to ~12.5 volts.
The new alternator is a 65amp from Ames, AC Delco VR. I do not have A/C, and this happens with or without lights, stereo or heater blower running.
I think the stock alternator was 58 amp, (not sure) and it has since been returned for the core charge.
Gen light comes on when hum is there, gen light dims gradually as RPMs climb and then goes out at 1,100RPM. This is full time issue and not limited to cold or warm engine.
Seems very odd I would have more volts at idle than at higher RPM.
Please any advice, greatly appreciated!

[stellar]

My first guess would be the regulator, and it's just a guess. Next guess would be brush hop in the alternator. It would be unusual for that alternator to have brush hop. Could be caused by weak brush springs, slip rings out of round, brush sticking in the brush holder. I'm curious as to why you changed the alternator and regulator. What was the problem before the changes?

[Here come da goat]

There was no real problem with functionality, I had removed the VR from the firewall to clean the area and the plastic tab that retains the wiring harness broke off. I simply replaced the alternator too at the same time because the case was pretty well weathered, discolored and pitted. Rather than disassemble and sandblast the case I took the easy route only to dress it up a little bit. Since the VR would have cost almost an additional $20 for shipping if bought alone, I added the alternator so together my total price exceeded $100 for the free shipping. It made sense to treat it as a $20 discount on a $69 alternator.

["QUICK-SILVER"]

Do any paint work during clean-up and the parts R&R?

Poor ground on the alternator and regulator will cause all kinds of problems.

Clay

[george kujanski]

^^^^ check regulator ground and the wiring from alt to regulator. Seems like perhaps the circuit from the alt R terminal to reg terminal 2 is flaky.'

If your reg has wirewound resistors on the back side, make sure they are not broken or a bad connection.

George

[Goatracer1]

At 12.5 volts the alternator is NOT charging. Like the others have said check the ground. If that is not the problem bypass the regulator and full field the alternator for a minute and check that is working.