Vintage DD turntables. Are we living dangerously?

*since the availability of the Feikert Speed App I have regularly stated that the Data downloaded on its 'Chart Info' was imprecise and non-scientific as it was not possible to duplicate the results from test to test.*

Why do we give credence to this in a magazine? Stereophile is Amateur Hour, unprofessional and lacking expertise. Too much trouble for them to conduct a proper test?
Read the specs page on the VPI Direct and all it has is the price.

I propose (without any data to back me up) that the tonearm has a lot of influence on the shape of the Feickert App speed deviations. I believe that unipivots are more easily excited by the 3D eccentricities of the records and thus show a more ragged perhaps more exaggerated trace. This belief is easily attributed to my dislike of most if not all unipivots but at the very least I think it safe to state that the w&f measurements are influenced by the tonearm and are therefore even less comparable from one table to the next.

Non-sequitur: I was at VPI yesterday and Harry Weisfeld is experimenting with adding additional pivot points to his 3D arms. Good idea.

Aigenga.
re unipivot arms.
You raise an interesting point, different arm bearings may well show a difference in the graphs. (Arm geometry may also show difference, as BT argues.)
That said, have any of the rigs recently listed by Halcro had unipivot arms?
The W&F visible on the raw data for the TT-101 seems to be quite similar from arm to arm. This would imply that the speed changes are localised in the drive unit itself.

I believe that Halcro posted three gimballed arms - the only unipivots that I noticed was the VPI on the Classic Direct. It showed a rather ragged trace.

I lean towards the idea that the regular speed changes on the Feickert traces are the results of record eccentricity; the fact that they occur once per rotation (16 - 17 per 30 second measured period) tells me that they reflect an out-of-round condition and are not due to speed correction feedback which would probably occur far more frequently.

Continuing my last post, I believe that the out-of-round condition must be in the record not the table because records are imprecise and therefore very likely to have that problem and if both the table and the record were at fault the trace would show them either reinforcing or canceling each other depending on where the record was on the platter - so every time you measured the same record on the same platter but rotated the record relative to the platter you would get significantly different results. This is easily tested.