Ancient stereo question--grounding

My ancient reassembled stereo, still consisting of components I bought in college over 30 years ago, has some kind of feedback hum. I vaguely remember that this is caused by not grounding my speakers, or something like that. (I don’t really listen to music much, as you might imagine. Mostly talk radio, where a little hum doesn’t matter.) Does anyone know what I’m talking about, and how this might be fixed? I’ve got Martin speakers, I think (the nametag has long since fallen off both) and each of them has four little posts in back, to which I’ve attached speaker wire to two posts apiece and have left the other two naked.

Any ideas? The hum isn’t terrible, but I can hear it when I play soft music.

Yea, I guess it could be a grounding problem. Is the hum 120 Hz? If so, you may want to replace the electrolytic capacitors in the power supply. They’re probably dried out.

Is the hum present in all play modes; turntable, CD, tape, radio etc.?
Does it show up on headphones?

Older plugs were non-polarized. I had some occasions when simply reversing the plug to the other polarity would stop amplifier hum.

I’m with Crafterman on this one. Chances are you have insufficient filtering on the incoming AC. Nice to know that replacing the caps can fis it. Thanks!

Just my phonograph. It shows up on speakers and on headphones both, but on neither when I’ve got the tuner playing.

Is the phono cartridge one of those modular plug in units, like this, with little pins on the back that slip into a socket on the tone arm?
If so, the pins can get dirty, the connection can get bad, and you’ll pick up hum. Try touching the tone arm to see if that alters the hum. If so, try reseating the cartridge.

Not exactly like that, but the same idea. FWIW, it’s got little numbers on it that read “D8E” (or “DBE”), and if I can figure out how to replace the cartridge it’s probably a good idea as I don’t have a clue which decade it was last replaced in. (The turntable is the newest component, as I have a vague memory of replacing it within the last fifteen years, with a model --Akai APQ60–that I picked up at a yard sale.)

The hum is unaffected by my lifting and setting down (on a record) the tone arm.

Is the turntable properly grounded with its ground wire connected to the amp? Sounds like you have a ground loop.

I will try anything, though I have no idea what a “ground loop” is and probably won’t get it no matter how eloquently you explain it.

I’m sure I set this system up by jamming various plugs into various outlets until it produced sounds, so I could easily have stopped before grounding the turntable.

Any idea how I’ll recognize the ground wire? Or how I ought to connect it to the amp? As I say, I’ll try anything once.

The ground wire usually has no connector on it, just bare wire that can be easily wound round the appropriate screw on your amplifier - it will be marked with the ground symbol.

There should be four wires coming out of your turntable’s rear chassis: power, audio Left and Right (combined on one wire) and Ground (usually a thin, black wire, either with a spade lug or a bare end). On the back of your stereo, usually next to the Phono inputs, there will be either a screw terminal - in which case you wind the bare end of the ground wire around it and tighten the screw, or a fancy model where you stick the end of the wire into a hole in the post and turn the screw around it by hand.

first things first, remember “ground” and “neutral” are completely different things. If you ground through the neutral wire, this will cause feedback therefore “hum”