What arm is this

[Lawrence001]

I bought a Pioneer PL-12D in immaculate condition. The original tonearm is in a box and there is a different one fitted. Does anyone recognise it?

The guy who sold it reckons his dad made his own tonearm in which case it might be a known DIY design. Or maybe he got confused about him fitting one vs actually making one.

I'm also a bit confused about what to do with the anti skate thing with string, there doesn't seem to be a weight or anything to attach the looped string to.



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[ianlenco]

I'm guessing that is a unipivot arm and the contraption to the side is to keep the arm level rather than act as a anti-skate.

[Lawrence001]

I'm guessing that is a unipivot arm and the contraption to the side is to keep the arm level rather than act as a anti-skate.

Thanks Ian are unipivot arms quite common in the DIY community? It lifts off a point in the base so I'm guessing that's the "pivot"?

Any idea where I would put the loop of string hanging off the end of the contraption?

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[Beobloke]

It does indeed look home-made. I particularly like the gentle undulations in the arm tube...

Frankly, I’d get the original arm back on there pronto!

[Lawrence001]

It does indeed look home-made. I particularly like the gentle undulations in the arm tube...

Frankly, I’d get the original arm back on there pronto!

There is a straight arm tube in the box as well. I wonder if he tried both and preferred this one. I wouldn't know where to start with this, looks like a great project for someone on here...

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[YNWaN]

I’m not so sure it is home made - if it is then it is very professionally finished. The mechanism on the side is the bias and works in a way I’ve not seen before - very clever in fact. The hanging thread would attach to the rear of the upper bearing assembly - near where the rear counterweight stub is (perhaps even around it). As the arm tracks the record it would cause the hanging weight construction to twist and therefore said weight will try to return to its resting position creating the required side force.. as the record is played the hanging weight will twist further and so gradually increase the amount of force applied.

Looking again at the hanging thread it may actually attach (loop over it) to the end of the counterweight stub.

The headshell looks very Decca like.

[Lawrence001]

I’m not so sure it is home made - if it is then it is very professionally finished. The mechanism on the side is the bias and works in a way I’ve not seen before - very clever in fact. The hanging thread would attach to the rear of the upper bearing assembly - near where the rear counterweight stub is (perhaps even around it). As the arm tracks the record it would cause the hanging weight construction to twist and therefore said weight will try to return to its resting position creating the required side force.. as the record is played the hanging weight will twist further and so gradually increase the amount of force applied.

Looking again at the hanging thread it may actually attach (loop over it) to the end of the counterweight stub.

The headshell looks very Decca like.

Thanks Mark that makes complete sense in terms of the physical setup (see photo) but the arm swings very strongly back to the start position when you lower it so something's not quite right. I did untwist the string when it arrived as it was tangled but I think I did it right. I can't see an obvious way of changing the force easily.

The gentleman who made it (now long retired) was a precision engineer in the aerospace industry at Smith's Industries and his son mentioned he used the workshop to make it (assuming it is not actually a commercial model), so it is quite nicely made yes.

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[YNWaN]

Given his skill set and access to equipment it possibly is home made then . The colour of the bearing assembly suggests stainless steel - perhaps even a titanium alloy. You might have to give the thread a negative twist before it is fitted to the stub. Looking at the trapeze arrangement it would suggest the small weight can be moved along the bar - presumably for some adjustment, though precisely how that would occur escapes me at present (will think on it ).

[scotty38]

Can you not unravel the thread along the uppermost bar so that the weight and assembly hangs lower? The lower it is (and longer the threads) the lower the twisting motion will be if so.

[YNWaN]

Oh, I think that if you move the weight along the bit of wire it hangs from it will alter the moment of leverage and so alter bias - I wouldn’t have thought it would be by much though.

At the start of playing a record the threads should be almost completely untwisted.