Advice for 78rpm needles for McMichael 365

[delaitt]

a few other questions related to the restoration of the pickup for this radiogram

1- does the induction motor need servicing such as greasing inside or not?
2- do you usually replace the worn out rubber grommets that attach the motor?
3- the motor does not appear to stop turning when the arm reaches the centre although the electric switch appears to work ok when activated by hand. have you come across this? I've attached a picture.

Thanks

Thierry

[Audio1950]

There should be an attachment on either the turntable or the centre spindle that strikes the little round roller as it approaches the centre of the record. If it was on the turntable it was simply a screw with a rounded head, so there will be an empty threaded hole in the side of the central boss under the turntable. If that hole is not there, then there was a tightly coiled spring with a protruding end that pushed over the centre spindle, then the turntable sat on top of it.

[PaulR]

Originally Posted by Hartley118

When you reassemble the pickup with its new rubber, be sure to centre the armature between the magnet poles. There's obviously a strong magnetic attraction that will tend to cause it to stick to one pole or the other. That ensures failure. It needs to be suspended centrally.

Incidentally, I've found that a soft rubber band can make an effective top suspension. So long as it's in the dark (which it normally is) then it'll last a good few years.

Good points! I have found that the choice of rubber for the top suspension is difficult. Too thick/stiff and the compliance suffers. To thin and the armature is not held centrally between the poles.

[PaulR]

Regarding the motor etc, you should dismantle it, clean it and re lubricate it. I use ordinary oil rather than grease.

The rubber grommets will need to be replaced at the same time.

As Audio1950 says the trip lever moves across as the arm moves and then is tripped when the lever on the spindle hits it. The lever on the spindle is adjustable for height using the two grub screws that hold it on. Here are two pictures. The first shows it about to trip and the second shows it immediately after tripping.

[Audio1950]

As Audio1950 says the trip lever moves across as the arm moves and then is tripped when the lever on the spindle hits it. The lever on the spindle is adjustable for height using the two grub screws that hold it on. Here are two pictures. The first shows it about to trip and the second shows it immediately after tripping.

That spindle attachment is different to the ones I have seen. The ones I referred to were tightly wound springs which expanded as the were pushed down onto the spindle. They both do the same job, though!

[delaitt]

Thanks for your replies.

I've now cleaned the motor and replaced the 3 x grommet rubber for the motor attachment.

I also retrieved the spindle attachment and the motor now stops.

However, the motor tends to stop when the head is half way through instead of being close to the end of the disc or centre. I tried to move the lever of the spindle attachement up and down but this has little effect.

The arm moves freely but it appears there is no spring to pull it back expect when the arm is pulled back.

Is there a special procedure to adjust when the motor should stop?

Thanks

Thierry

[PaulR]

This is something that is easily demonstrated in the flesh but difficult to explain in writing...

The lever which is tripped by the spindle lever is pivoted at its other end. There is a spring which gently pushes it down onto the roughly triangular shaped piece below it. The main lever is only lightly coupled to the "triangular" piece.

The triangular piece is coupled to the arm and moves to the left as the arm tracks across the record. It pulls the main lever with it. When the record is about half way through playing the rubber buffer begins to touch the lever on the spindle.

As the main lever is only lightly coupled to the triangular piece the spindle lever simply knocks it back each time it revolves. This continues until the arm reaches the end of the record and is moved in more rapidly by the runout groove. When this happens the friction between the triangular piece and the main lever means that the spindle lever is knocked harder and cannot move out of the way quickly enough. This actuates the motor switch.

You should be able to see a brighter track in the triangular lever where the main lever rubs over it as the record progresses. I would think that, due to age and lack of use, the friction along that track is a little too much and the main lever cannot jump out of the way as it should. A little oil and working the levers over each other should cure it. The spring can be adjusted by the little screw at one end but this will have been set up in the factory and I would not alter it.

Phew!!!

[PaulR]

PS. It occurs to me that if you are trying it by moving the arm across manually you may be moving it too fast and tripping the switch. In that case, try moving it very slowly as it would if a record was playing and you may find that it is actually working correctly.