Vintage DD turntables. Are we living dangerously?


I have just acquired a 32 year old JVC/Victor TT-101 DD turntable after having its lesser brother, the TT-81 for the last year.
TT-101
This is one of the great DD designs made at a time when the giant Japanese electronics companies like Technics, Denon, JVC/Victor and Pioneer could pour millions of dollars into 'flagship' models to 'enhance' their lower range models which often sold in the millions.
Because of their complexity however.......if they malfunction.....parts are 'unobtanium'....and they often cannot be repaired.
128x128halcro
Dover.

The essence of an I beam and ply is the separation of the two outer layers (sheets). Any bending causes compression of one sheet and tension in the other. This increases the stiffness of the structure.
As I said earlier. It is a 25 year old design. Were I to design one today, it would use different materials and architecture.

(Dover "To be clear what was being measured in my post on the Timeline thread – the 2mm lag was generated by setting the TT speed with no stylus playing and then measuring the lag when playing. A 2mm lag at a radius of 400mm is a speed error of 0.08%") and ("In summary, your maths is wrong because your calculations are based on a misinterpretation of my Timeline test results.. When the 26kg platter speed was set with the stylus playing, there was in fact no measurable retardation.")

My post calculates the retardation torque required to cause the slowing, from stylus raised to stylus lowered and then applies this to the pod.
What happens AFTER you adjust the speed with the stylus lowered makes no difference to the calculated pod movement.

Re the CofG of the crescent shaped pod. I didn't make this note clear. It appears that the feet have been moved back towards the rear of the pod, moving the CofG closer to the front feet. The photos are a little ambiguous. If this is not the case then yes the CofG will move away from the front pod feet reducing the tilt.

The platter is heavier than I thought. If its radius of gyration is as I assumed, this extra weight will increase the torque required to slow it and by definition increase the pod tilt.

Jmowbray.

More information on the upgrade is available on my web site. The procedure is now available for the SL-1200 series.


Please PM me or contact me via my Krebsupgrade web site for a detailed description.

cheers.
05-14-15: Richardkrebs
Dover.
The essence of an I beam and ply is the separation of the two outer layers (sheets). Any bending causes compression of one sheet and tension in the other. This increases the stiffness of the structure.

Richardkrebs, that is not correct. if you used sheets of plywood stacked vertically to make an I beam your house would sag and probably fall down. The essence of an I beam as I explained in my post is that the vertical component has high vertical and longitudinal strength, but can be flexible in the lateral direction. It has nothing to do with the layers of timber in the wooden I Beam. In actual fact plywood as you understand it is not used in the manufacture of I beams. I Beams use a special construct of layers of timber running in the same direction to give the structural longitudinal strength. Plywood has the layers arranged with the grain crossing at 90 degrees with each layer.
It might help if you look at a metal I beam to understand the concept - there are no laminations in a metal I beam, but if you removed the top and bottom of the I then the beam will flex like a sheet of metal.
Dover.

Please read my post again.

I did not say that one should make an I beam with stacked ply.
Ply AND "I" beams use a similar technique to separate the outer layers where any bending causes compression in one layer and tension in the other.

Why are we debating this???
5-14-15: Richardkrebs
Ply AND "I" beams use a similar technique to separate the outer layers where any bending causes compression in one layer and tension in the other
Why are we debating this???
Richardkrebs you described your plinth as a "form of I Beam".
05-13-15: Richardkrebs
My TT uses 2 x 30mm thick Acrylic sheets, separated and fused to a lead spacer. By separating the two structural plates a form of 'I' beam is produced since shear between the two plates is strongly resisted.
This is a similar idea to that used in the light weight wooden 'I' beam floor joists.
An I Beam consists of a Web with a flange top and bottom.
Your plinth that you describe has only a Web and no flanges.
An I Beam without flanges is structurally weak, has no axial strength and will flex. Here is a link to help you understand how I Beams work..
http://en.wikipedia.org/wiki/I-beam
There is no debate. The plinth that you built is laminated sheets of acrylic and lead and is not an I Beam, nor is it even a form of I Beam as you have claimed.