Moderators: Dave Moll, Andrew Davie, Steve Anderson
Steve Anderson wrote:A good old-fashioned 'record player' that is mains powered will probably use a synchronous motor - I think called 'shaded pole', but I'm not certain. But better (expensive) and more recent 'Hi-Fi' turntables will often use a direct-drive motor which requires quite a bit of support electronics. They are generally low-voltage too.
You'd be looking for a donor record player (or a radiogram) from the 50s/early 60s probably. If you're lucky it'll also have a transformer for the the tube/valve amplifier, useful for CRT stuff...
Steve A.ir
Also, and I hate to say this, tape recorders...
...a trip to the local dump/tip/recycling place may be in order...
Be careful, if they've sat unused (probably) for many years check if you can turn the motor spindle to see if it's free and not seized. If it is get some penetrating oil, apply to the bearings every few days - gently try and turn the rotor with your fingers, if it doesn't move - more oil, more time...do not use pliers, mole-grips or any form of tool to move it...I've brought quite a few back to life this way....patience is the by-word, it can take weeks to free up...warmth (but not too much) helps, not really Melbourne's strong point!
Steve Anderson wrote:Photo shows a synchronous motor revived in a UK made tape recorder from the early 60s. Generally they'll look similar. Also note the power transformer for the valves/tubes and the smaller audio output transformer.
Some may only have a single winding, mainly record players as the motors don't need the power or torque for fast-spooling the tape.
Steve A. (Somewhat of a tape-head).
The photo reminds me of open-heart surgery!
Viewmaster wrote:You have so many CD's Harry that you will need an auto changer
like this 78 RPM job.
Klaas Robers wrote:These motors are weak motors, if you need a higher speed, say 1 rps, 60 rpm. But from the film I realized why the turn table in our microwave runs sometimes to the right and sometimes to the left. The problem with simple synchronous motors is that they don't start. I had once an electric clock that did not start, and you had to give it a swing before it ran. You might know this from an old bike dynamo. You can use it as a motor on 50 Hz (then it runs on 12,5 rps!) but it should be started by hand, or by a small DC-motor. We used bike dynamos as motor for running a Nipkow disc.
The motor of the microwave had a provision that it will start, but you don't know which direction. That depends from the moment that you switched it on, the phase of the AC at that very moment. Learnt something.......
I got two Philips synchronous motors, that run on 230 volt, with a capacitor, 250 rpm. One has a universal gearbox screwed on, that you can configurate for quite some output speeds. I have all documentation of them. If you want to have it..... Should I ship it to Australia?
Klaas Robers wrote:The record player motors and the motors in tape recorders are almost always so called "asynchronous motors". They try to keep up with the mains frequency, but they always run slightly slower. This lower speed gives them the torque, the more torque you need, the slower they run. The advantage is that they start very reliable from a speed of zero (high torque).
The old 78 rpm players needed a really high torque in the beginning, when playing at the outerside of the disc. They had realy large motors. Later the players were optimized for 33,3 rpm and 45 rpm, while the weight of the pick-up head was much lower, so a much lower torque was asked for and smaller motors could do the job. For 78 rpm, with a much lighter pick-up, the motor was just powerful enough.
Klaas Robers wrote:...I did that for a mechanical clock that was designed for 60 Hz, which I could only make with the aid of a quartz crystal, divider and a power amp.
Klaas Robers wrote:Wear on the "idler" wheel does not change the speed. The speed at the inner side of the platter is equal to the speed of the outer side of the motor. And as the metal parts are not wearing out, the speed will not change. Only when the rubber wheel wears to unround, you get speed changes.
The type of motor that you described, the shaded pole motor, gives torque on the slip (small reduction in speed) of the motor. That is the reason that with some braking force (edy current), you can change the speed somewhat. This is contrary to a synchronous motor, which runs exactly the speed of the mains, or it stalls. The difference is the rotor: for a synchronous motor it is a strong magnet, for a asynchronous motor it is a cylinder of iron with a copper structure in it.
If you want to fine tune the speed of a synchronous motor, the only way is to change the frequency of the powering voltage. I did that for a mechanical clock that was designed for 60 Hz, which I could only make with the aid of a quartz crystal, divider and a power amp.
Speed control for the asynchronous motor, you know.
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