I think you're both saying the same thing. Assuming you're in the States and have a 60Hz light source available, then take the standard '300 rpm 50/60Hz' strobe disk found on, say, the TM100. The '60Hz bars' will let you check a 300rpm spindle (obviosuly), the '50Hz bars' _used with a 60-Hz lamp_ will check a 360rpm spindle. -tony

Of course it is. I believe you can do it for any speed and light frequency, sctually. 50Hz presumably is 100 flashes/second (I am assuming you are using a mains-energized neon lamp or something). First try making one for 300 flashes per second. That one is trivial, 360rpm is 6 revs/second, so 1/50th of a revolution per flash. So 50 spots works. Now realise that said disk will also work at 100 flashes per second. The fact that a given spot has moved 3 positions, not one, between flashes is not noticeable since all dots look the same This is actually a problem with strobe disks. A disk that will indicate, say, 360rpm will also appear to be stationary at 720rpm (or any integer multiple of the speed). I susepct you'd notice if your disk drive was spinning twice as fast as normal, but I would alwaus check the index pulse timing 'looks sensible' There should be (here) 6 index pulses per second. You can check that quite easliy with a 'scope or counter. The result will not normally be accurate enough to set the speed, but it will make sure you're near enough the right speed that the stroboscope will let you lock to that speed, not twice it or whatever. -tony

Hi 75 is a lot of bands. I'd think that it would need to be a larger disk. Still 45 for a 60 Hz would be 90. Are you sure your not thinking of 33 1/3. That is a lot tougher or 78. Dwight _________________________________________________________________ Put your friends on the big screen with Windows Vista? + Windows Live?. http://www.microsoft.com/windows/shop/specialoffers.mspx?ocid=TXT_TAGLM_CPC…

Hi I got my math wrong. The fellow is also wrong. 45/60 = .75. 100/.75 = 133.333.... If rounded to 133, you get 45.11278195---- Still, using Tony's multiple method, 400 dots would work fine. It would be a large disk but it would work. Dwight _________________________________________________________________ Connect and share in new ways with Windows Live. http://www.windowslive.com/connect.html?ocid=TXT_TAGLM_Wave2_newways_112007

Incidentally, I asked a friend wbo is both a classic computer enthusiast and a musician if there would he any audible difference between playing the record at 45rpm and at 45.11 rpm. He said he didn't believe anyone could tell them apart. So I susepct the only people this matters to are the audiophools. Actually I am suprised nobofy has tried to sell said audiophools a crytal-controlled lamp to view the strob disk with. Or amybe they have and I've not noticed it yet. It's hardly 'my method'. I certainly don't claim to have invented it, but alas I can't find a reference to it. I am not sure when stroboscopes were invented, I susepct they pre-date electricity, though. Certainly stroboscpinc tuning forks exist -- these a tuning forkes with slotted vanes on the tines (they are designed to have the extra mass of said vanes, of course)< you view the stroboscopic disk (or wahtever) through the slits. To make this marginally on-topic,such tuning forks were used, at least in the UK, to set the speed of teleprinter motors. Creed teleprinters have series-wound motors with a governor assembly on the end of the motor, and you viewed the black and white stripes on the governor cover through such a tuning fork. Somewhere I have a trleprinter test set (an ATE (manfufacturer) TDMS5 if you know about such things). The master oscillator not only drives the ring counter that acts as the transmit distributor (the whole thing is valved, BTW), but also a neon lamp on the panel. You are supposed to view this lamp trhough one of said tuning forks and effectively 'zero beat' the bulb agianst the fork to get the oscillator on-frequency. One other thing to be aware of. The ideal strobosope has very narrow flashes of light with larger gaps between them. If you are using a 'harmonic disk' (or whatever you want to call it), you need to get closer to this ideal than for a normal disk (at leat to get a very clear pattern). Of coure a real xenon-tube strobe does this, a mains neon bulb may not. -tony

And.... that would be completely offtopic. Re: record speed

Tony wrote... I agree completely with your opinion. It was on topic. Then topic-drift occured.... ;) That is way-on-topic... thanks :) Jay

The "he" is me... I've swapped drives originally and this drive worked for a short time. I was originally looking for common failure modes for these drives. I've cleaned the heads using a disk but a more thorough and direct cleaning is warranted. The problem is that this is the second drive in the pair and to get to it means I have to disassemble half of the unit. I just haven't had the time in the last few days. I also want to check the drive RPM. I found a program for the Model 100 and bar code reader which turns it into a stroboscope, but I wanted to validate it on a working drive, so I have to pull out a TM100 drive. But, alas, I haven't had time for that in the last few days, either. I'm going to try to do that today. Rich On 11/27/07 12:08 AM, "dwight elvey" <dkelvey at hotmail.com> wrote: Rich -- Rich Cini Collector of Classic Computers Build Master and lead engineer, Altair32 Emulator http://www.altair32.com http://highgate.comm.sfu.ca/~rcini/classiccmp

I think he's probably wrong. Most people probably can't, at least not without a side-to-side comparison (I could sure hear the beat frequency if listening to 450Hz and 451.1Hz together, but feel sure I could not tell the difference in isolation, likely not even in a non-simultaneous A/B listen). But some of people with better "perfect pitch" (which actually isn't perfect, just substantially more precise than most people's pitch sense) could, I expect, tell you which is which even in isolation. One other thing is that mains frequency may not always be a good 50/60 Hz reference (which will, of course, affect things like the floppy speed calibration that started this thread off, if it's using the power mains as the frequency reference). The power utilities go to some lengths to make sure it averages out to that over periods measured in days, because of all the clocks that depend on it. But in the short term - seconds and minutes - I've read that it can vary slightly (the figure I recall is 1Hz or so) for various reasons, at least one of which is deliberate compensation for the others. :) I'm not sure how plausible this actually is. Given how mains power distribution works, it seems to me that the entire grid must perforce be running at the same frequency, or parts of it will drift in and out of phase with other parts, causing problems at the various points where one utility sells power to another. This means that tweaking the frequency would require grid-wide collaboration, difficult even for grids as small as England's, that much more so for grids like the North American one. Or do they use monster M-G sets or the like to deal with that? :-) /~\ The ASCII der Mouse \ / Ribbon Campaign X Against HTML mouse at rodents.montreal.qc.ca / \ Email! 7D C8 61 52 5D E7 2D 39 4E F1 31 3E E8 B3 27 4B

Kill this thread on record speeds please. Jay