Stroboscopes for phonographs?

[menophanes]

Some forty years ago I made (by hand) a stroboscopic speed-checker with 125rpm and 160rpm bands for my Model A Standard and mounted it on the end of the mandrel. I have just been trying to create another for my new machine, but my skills seem to have declined to the point where I can no longer draw out the divisions accurately. I am wondering, therefore, whether a pre-printed stroboscope of the appropriate size and calibration is available anywhere. Furthermore, I have forgotten the formula for establishing the number of divisions corresponding to a given speed, and I cannot find it anywhere.

According to Frow & Sefl, a stroboscope with 74 divisions should register 160rpm when used with British (50-cycle) mains electric lighting. I worked out that if I drew a circle 177.8mm in diameter (with a circumference, therefore, of 370mm) and drew lines from the perimeter to the centre exactly 5mm apart measured along the circumference, this should give me the right calibration for 160rpm. (My idea was that I would then scan this and scale the resulting image down to the diameter of the mandrel.) The problem is that I cannot seem to space out the lines accurately enough; consequently I am stuck for the moment.

There used to be an online facility which would design a stroboscope automatically once you had input the desired RPM and AC-cycle figures, but this seems to have vanished. Can anyone help?

Oliver Mundy.

[alang]

Try here www.christerhamp.se/phono/strobo.html or here forum.talkingmachine.info/viewtopic.php?f=7&t=637

Hope that helps.
Andreas

[alang]

Forgot to mention this option. Been using this for years, because it is not dependent on the electric mains frequency. Works like a charm and isn't expensive: www.amazon.com/AGPtek-Professional-Digital-Tachometer-Contact/dp/B004Q8L894/ref=sr_1_4?s=automotive&ie=UTF8&qid=1490980951&sr=1-4

Andreas

[menophanes]

Thank you, Andreas! As a beginning I have used the 'Strobo' programme to create a grid for 158 r.p.m. (choosing this speed rather than 160 because it results in equally-spaced divisions on the 50-cycle setting). I then took a screenshot of the resulting image, saving it as a TIFF file which I can now re-size or otherwise edit in any graphics programme. When I have done this and set up similar files for some other speeds I shall post the results here in JPEG form.

Oliver Mundy.

[nefaurora]

No offense.. but the actual use of a Stroboscope today is pretty much Obsolete unless you want to further entertain yourself.

If you want the "MOST" accurate RPM reading, and be able to do it so fast that your head will spin, Pickup one of these Digital RPM Gauges off of Ebay. It is a "MUST" buy if you are a "PHONOHEAD" or PHONOGEEK... I own two of them!!....They are very easy to use and even come with instructions! You'll never need a Stroboscope again unless you want to be Nostalgic...

I usually time the Speed of my machines at 161 or 162 RPMs WITHOUT a cylinder playing. This is done because while a Cylinder is playing, You have to take into account "Cylinder Drag" from the Drag of the Diamond Needle or Sapphire Stylus, and also Gearing, and/or Belt drag taken into account. Do this, and the Machine should run at 160 RPMs with a cylinder playing. You can always check yourself and your work with the Digital RPM Guage! That's why it's great! See Ebay weblink below:

www.ebay.com/itm/Digital-Laser-Photo-Tachometer-Non-Contact-RPM-Tach-Meter-Motor-Speed-Gauge-USA-/140666635376?hash=item20c0628470:m:mLo41C8sTMQey8uXCveMR4Q

Phonograph Digital RPM Guage Pictured Below:




)

Tony K.

Edison Collector/Restorer

[menophanes]

Thank you. I have found what looks like the same device on British Amazon at GBP14.98 including postage and have ordered it. The one mentioned by Andreas appears to be another example of the same product.

Oliver Mundy.