Lazarus Lathe Project

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markrob
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Re: Lazarus Lathe Project

Post: # 44748Unread post markrob
Sun Nov 13, 2016 10:33 am

Hi,

You are right on about the need for the diode. LED's have very low reverse voltage specs (on the order of 5V IIRC). So the diode is needed. One thing to ponder. As you have it, the LED flashes at the AC mains frequency (50hz in your case). Most strobe disks I've seen are designed with a 2X flash rate in mind. Either the florescent or neon lamps typically used flash on each half cycle of the AC waveform. Its not a big deal, since you are undersampling by a factor of 2 and the disk works the same (2 lines go by for each flash). You could make you own strobe disk with less lines or remove the 1N400x and add a second diode with reverse polarity and get double the flash rate. The number of lines needed for a disk is given by:

Lines Per Rev = Strobe Flash Rate x (60 / Turntable RPM).

I checked an old Robbins disk I had here on the 78 band, and counted 92 lines. Note that the actual standardized speed for 78 RPM records is really 78.26 RPM

https://www.library.yale.edu/cataloging/music/historyof78rpms.htm

Using the above formula you get 120 * (60/78.26) = 92.001 This is based on the AC line frequency here at 2 x 60hz or 120hz

Mark

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Soulbear
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Re: Lazarus Lathe Project

Post: # 44749Unread post Soulbear
Sun Nov 13, 2016 12:31 pm

Hi Mark,
markrob wrote: You are right on about the need for the diode. LED's have very low reverse voltage specs
Thanks for the input, I suspected as much with the LED's. I've now "Doubled" the Flashrate by going with these Small Neon's
Neon Indicators.jpg
The 50Hz LED Flashrate seems to make the OverSpeed look a Little Greater in the first Video than I observed with the Naked Eye, Using the Neon's brings the Video much "Closer" to what I See when Running the Speed Test. These Neon's have quite a Low-level of Brightness, as supplied with a 150K Dropper Resistor. I paralleled another 150K Dropper Resistor with it, in an effort to "Brighten" the Neon's, and still it was just not quite Bright Enough for Video Purposes, so I did the same with a Second Neon "Doubling UP" and using both. I've then managed to Make another "Strobe" Video. Whilst still not 100% perfect, hopefully this will "Better Demonstrate" how little the Platter Speed is Off.
Lazarus Lathe Strobe Test2.3gp
Regards :wink: :P :D Soulbear
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grooveguy
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Re: Lazarus Lathe Project

Post: # 44751Unread post grooveguy
Sun Nov 13, 2016 1:09 pm

Markrob makes a good point about the strobe discs, as historically they were designed to stand still with 2 flashes per cycle of the mains, although they should work with a flash rate at the fundamental mains frequency as well. In fact, you can see a stroboscopic effect of some sort even with an incandescent lamp of modest wattage.

Do you note that, with the neon bulb, the strobe segments seem more clearly defined? I think this is because the neon is nonlinear. It has a 'striking' voltage of 60V or so, and then luminance increases to some degree according to current as the mains cycle increases in amplitude. With the LED, it probably starts to glow near the zero-crossing and is more linear with current. I'll bet if you stuck a zener in series with either light, so that the LED or neon flashed only near the peak voltage of the mains, the segments would appear sharper still. That is, they would not be illuminated over a greater part of their circular travel.

I just recalled that one brand of LP record had the image of strobe disc printed at the outside edge of the label. Never checked to see if it was really a strobe, could have been just for show.

Of course this is all hypothetical, academic and completely off the subject of disc recording. This digression is certainly not meant to derail thought along those more august, important and to-the-point lines. Please excuse.

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Soulbear
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Re: Lazarus Lathe Project

Post: # 44752Unread post Soulbear
Sun Nov 13, 2016 1:45 pm

Hi grooveguy,
grooveguy wrote:This digression is certainly not meant to derail thought along those more august, important and to-the-point lines. Please excuse.
No such excuse is needed grooveguy, it is aways a pleasure to read of other Trolls thoughts and idea's, whether these are to make a "Serious" Point, are Specifically Related to the Post, or are even Tangental and Whimisical. Oftentimes such inputs can then in turn, cause the reader to make their own discoveries, while looking into whatever's been raised or suggested, by the spotaneity of the other contributor's inputs. In my own view, Anecdotes and Stories are a great and often overlooked resource, and can often impart more knowledge and information, than the reading of reference or other educational material, certainly it's more fun!!
Regards :wink: :P :D Soulbear

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Gridlock
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Re: Lazarus Lathe Project

Post: # 44753Unread post Gridlock
Sun Nov 13, 2016 1:55 pm

<\\\\\\\\\\\\\\\\\\\\\[[[[[[[\/]]]]]]]\\\\\\\\\\\\\\\\\>
Recordette Sr.......Presto K-8

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Soulbear
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Re: Lazarus Lathe Project

Post: # 44754Unread post Soulbear
Sun Nov 13, 2016 2:30 pm

Gridlock wrote:Tangential
"Typography is the art and technique of arranging type to make written language legible, readable, and appealing when displayed"
Thank you. It's most kind and thoughtful of you to point out my Typograhical Failings. I'm sure you'll make allowances in the future when I inform you of my age-related Failing Visual Acuity and the Painful Medical Condition I that suffer from called Dupuytrens Contracture, which sometimes makes typing a real challenge for me. If you are unfamiliar with this condition here's a brief synopsis.
"Dupuytren’s contracture (Dupuytren's disease) is a condition that affects the hands and fingers. It causes one or more fingers to bend into the palm of the hand. It can affect one or both hands, and sometimes affect the thumb"
I'm also quite sure that in one so observant and critical, that you've never made a Typographical Error in your life.
Best Regards :wink: :P :D Soulbear
Last edited by Soulbear on Sun Nov 13, 2016 2:39 pm, edited 2 times in total.

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markrob
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Re: Lazarus Lathe Project

Post: # 44755Unread post markrob
Sun Nov 13, 2016 2:33 pm

Hi,

The Audio Fidelity Label had the strobe.

http://www.cvinyl.com/labelguides/audiofidelity.php

Mark

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grooveguy
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Re: Lazarus Lathe Project

Post: # 44757Unread post grooveguy
Sun Nov 13, 2016 3:02 pm

Right you are, Mark; AudioFidelity it was!

And, Soulbear, I think that Gridlock was not calling attention to your typo, but simply linking us to another article having to to with the stroboscopic effect. Anyway, I'll be YOU have never misspelled a word in the front-panel artwork of a commercial product. Now THAT is embarrassing, believe me.

Anyway, Gridlock, thanks for the interesting 'Dream Machine" tidbit. Admittedly interesting, but now that California has legalized the recreational use of marijuana, sort of the long-way-round... whoa, Dude!

However, it did take my memory back to something that I found fascinating years ago in an early '60s issue of the Journal of the SMPTE, and may or may not have any bearing on Biron Gysin's bus trip to Marseilles. It's a phenomenon explained briefly here, with a link to a further magazine article:
http://www.earlytelevision.org/butterfield.html

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Soulbear
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Re: Lazarus Lathe Project

Post: # 44758Unread post Soulbear
Sun Nov 13, 2016 3:09 pm

Hi Mark,
markrob wrote:he Audio Fidelity Label had the strobe.
Now what I thought was simply some Fancy Pants Platter Mat Design I.E. this:-
Connoiseur Lathe12.JPG
Could this really be a "Strobe" Platter Mat?? Furthermore, also on the Platter Spindle is a Similarly Marked Aluminium "Diskette" I went to the bother of buying some "Gold" paint, and have "Restored" the 1 missing mark on the Rubber Mat. MMMmmm just maybe it IS a Strobe Mat & Diskette eh?
Regards :wink: :P :D Soulbear
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markrob
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Re: Lazarus Lathe Project

Post: # 44770Unread post markrob
Sun Nov 13, 2016 4:51 pm

Hi,

Sure looks like a strobe platter. Count the lines on 78 band and see if it fits the formula based on 50 hz.

Mark

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Gridlock
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Re: Lazarus Lathe Project

Post: # 44776Unread post Gridlock
Sun Nov 13, 2016 6:20 pm

Soulbear that was not my intent. In fact I spelled it wrong myself but my telephone corrected them Spelling's
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grooveguy
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Re: Lazarus Lathe Project

Post: # 44779Unread post grooveguy
Sun Nov 13, 2016 8:19 pm

Mark:

Help me with my math(s) here, if you will. Assuming the US-standard speed of 78.26 r.p.m. and a 50Hz mains frequency (100 flashes per second), for the spokes to stand still there have to be 100 spokes in 1.30433333 revolutions, or 76.66 of them in one revolution. Over here, where the mains frequency is 60Hz, or 120 flashes per second, there would be 92.0010 of them. Sure enough, I counted the spokes on my 1950's vintage strobe disc, and it had 92 segments (pretty close).

I'm not exactly sure where 78.26 comes from, but it was my understanding that it had something to do with gear-driven turntables and hysteresis-synchronous motors. At least that was the method of the madness with respect to 33-1/3 r.p.m., with its roots in early synchronized-disc sound movies. A (US) synch motor running at 900 r.p.m. and a gear ratio of 27 fits nicely in that supposition, but leaves the 50Hz world (750 r.p.m.) out in the cold. Of course there was no need to synchronize film and phonograph records over there, I guess, but accurate playback of broadcast transcriptions was at least one demanding necessity for close program(me) timing. (When tape replaced discs over here, network broadcasters lamented the timing accuracy of a disc transcription.) So I wonder if 33-1/3 r.p.m. over there would ever have been a standard, or by the time it became a matter of sharing LPs across the pond, most turntables were puck- or belt-driven with the possibility of infinite 'gearing' ratios.

In any event, I would think that your strobe discs would have 77 segments, indicating an actual turntable speed of 77.922 r.p.m. when standing still. 76 segments, would stand still at a speed of 78.94 r.p.m.

Regardless, all this is giving me a headache; I need a beer.

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markrob
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Re: Lazarus Lathe Project

Post: # 44780Unread post markrob
Sun Nov 13, 2016 8:58 pm

Hi,

I think you got it right. In Soulbear's photo of the Sudgen mat, I counted 38 lines in about 1/2 of a revolution (best I could do given the photo). So that agrees with your calculations. As you point out, that's the best you could do given the flash rate of the AC mains. If you read the link I posted on the 78 standard, you can see that they did indeed base the speed on integer values of motor speeds and numbers of gear teeth (3600 RPM/46 tooth gear). That implies that a 50 Hz motor would not be able to reach the US standard of 78.26 RPM easily using a simple direct gear drive. In fact a US 3600 RPM motor running at 50 Hz would run at 3000 RPM and a 38 tooth gear would result in 78.95 RPM. That's the same speed a 76 line strobe disk would yield as you point out. So maybe the UK standard is 78.95 RPM??

On the other hand, 33.333 RPM works out to exactly 180 lines at 50 hz (216 at 60 Hz). 45RPM works out to 133.333 lines at 50 Hz and exactly 180 lines at 60 Hz. The errors are pretty small, but present. If you are inclined, you can correct for the accuracy error if you count the number of strobe lines that pass an observation point in a known period of time.

Mark

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Soulbear
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Re: Lazarus Lathe Project

Post: # 44787Unread post Soulbear
Mon Nov 14, 2016 6:52 am

Hi There,
Gridlock wrote:Soulbear that was not my intent. In fact I spelled it wrong myself but my telephone corrected them Spelling's
I'm most pleased to hear it, thanks.
grooveguy wrote:In any event, I would think that your strobe discs would have 77 segments, indicating an actual turntable speed of 77.922 r.p.m. when standing still.
grooveguy, 77 is indeed the Magic Number!!! So the Platter Mat is also a 60 Year-Old Stoboscope Disc, well I'll be blowed, fancy that!! My eyesight is not up to checking the Aluminium "Diskette" as is, but with my curiosity piqued I could possibly "Scan" it and then enlarge it, to read it On-Screen. I think though that I'll not bother, and simply take it as a given, that it too is a Functional Stroboscope Disk.
Regards
:wink: :P :D Soulbear

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Soulbear
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Re: Lazarus Lathe Project

Post: # 44788Unread post Soulbear
Mon Nov 14, 2016 7:51 am

Hi Trolls,
grooveguy wrote:The little clips in my photo are something I ran across first in 1958 or so. They were called "diode clips" at the time, testament, I suppose, to the fragility of semiconductor devices of the day. It's 's been nearly 60 years since I bought those, although I remember the day clearly. They were not a big mover at the parts store, and I had to paw through the shelves myself to find them. They were manufactured by Cambion Corp. and, believe it or not, still are! Here's what I found easily on the Web: The current product is quite similar to mine, although the hex base in my photo doesn't really show in the Cambion drawing. Anyhow, for your convenience, the UK branch of the firm came up first!
The Telephone Sales Lady supplied me with a Sample, with the only Clip they had in stock, and which arrived over the Week-end. To Test-Mount the Clip, I drilled and Tapped @ 2mm some Phenolic Board, (over here in the U.K. it's branded "Tufnol") What can I say?? The Cambion Spring-Loaded Contacts recommended by grooveguy are "Perfect" for this Application.
Cambion Contact-1.jpg
Cambion Contact-4.jpg
Cambion Contact-3.jpg
The Sales Lady indicated that it was possible that some of the Sales Rep's might have further samples and to contact the Company this A.M. when the Rep's would return "En Masse" from a Trade Show overseas in Deutschland. I duly made a call but frustratingly with the same outcome, Absolutely Non to be had, unless it's a Minimum Quantity of 500 !! :evil: HUMPF!!! Te He!
Regards :wink: :P :D Soulbear
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Soulbear
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Re: Lazarus Lathe Project

Post: # 44789Unread post Soulbear
Mon Nov 14, 2016 10:41 am

Hi There,
markrob wrote:add a second diode with reverse polarity and get double the flash rate
Hi Mark, I'm afraid I'm as guilty as charged, and went for the simplest solution of using just Half of the Secondary Winding of the Transformer. This of course resulted in the LED only producing a "Flash" on the Forward Half-Cycle. Following your advice and "Center Tapping" the Transformer, thereby using both of the Secondary Transformer Windings, combined with Installing a "Second Diode" as you suggested has indeed paid dividends :-
DIY Stroboscope1.jpg
The "Flashrate" of the LED has of course "Doubled" and has produced much better definition (At least I Think So!!) in the video :-
Lazarus Lathe Strobe Test3.3gp
Regards :wink: :P :D Soulbear
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grooveguy
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Re: Lazarus Lathe Project

Post: # 44791Unread post grooveguy
Mon Nov 14, 2016 11:34 am

Beautiful, Soulbear,

Obviously the camera has trouble focusing, but still it's obvious that the definition of those segments is much better. Good job!

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Soulbear
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Re: Lazarus Lathe Project

Post: # 44825Unread post Soulbear
Thu Nov 17, 2016 4:22 am

Hi Trolls,
At last I've got a an Half-Decent way to demonstrate how close the Platter Speed is to "Ideal" following the Conversion of the Platter Speed from its Designed 78RPM to its "New" 45RPM. I've utilised the Lathe Mat from my AR Sugden "Connoisseur" Lathe and Placed it on the DR33C's Platter. I really don't know why I didn't think of this before now, but I think I've now made ammends for this attack of "Brain Fade"
BSR DR33C Restoration-80.jpg
While I was at it, I also checked the little Aluminium Sugden "Strobe" Diskette. Whilst the Focus from my Camera Phone is still not the best, both the Video's can hopefully Now Finally "Clearly" show other Trolls, how little the Speed is Off, by observing the "Very Slow" Forward Advance of the Strobe Markings, following this Platter Speed Modification.
BSR DR33C Connoisseur-Mat.3gp
BSR DR33C Connoisseur-Disk.3gp
Regards :wink: :P :D Soulbear
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grooveguy
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Re: Lazarus Lathe Project

Post: # 44827Unread post grooveguy
Thu Nov 17, 2016 12:32 pm

Hello, Soulbear,

The little disc shows a very sharp image in your video, and indicates that you may need to hold a piece of sandpaper against that drive spindle, or perhaps have your machinist 'kiss' a bit of metal off the circumference.

I suppose one could count the segments that 'slip by' and calculate the speed error, but may I offer an alternative? I have scanned a strobe disc I obtained nearly 60 years ago and have attached the image. This disc has not only the four common turntable speeds, but also bands for ±2% and ±4% from nominal. From this it's easy to calculate a speed error within these ranges. For example, if the +2% and +4% bands are counter-rotating at the same rate, obviously the turntable is 3% fast.

Of course we're talking digital here, not analog, so the percentages are probably best approximations. I mean what if it needed 73.256 segments to be truly accurate? Probably pretty close, however.

The original disc is about 9 inches across and barely fit my scanner. Even when printed on US 'letter' paper, a bit wider than your A4, the edges would be cut off. So reduce this as required, affix it to a piece of cardboard, and you'll have a useful tool.

UPDATE: As Homer Simpson would say, "Doh!" In my eagerness to be helpful I totally forgot that this strobe disc will do you absolutely NO GOOD, as you don't have 60Hz mains. I certainly meant well, however. Perhaps you can fabricate something like this for yourself. (I feel quite foolish now, perhaps I'll go out to the street, pour gasoline over myself and strike a match.)
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Soulbear
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Re: Lazarus Lathe Project

Post: # 44828Unread post Soulbear
Thu Nov 17, 2016 2:23 pm

Hi grooveguy,
Aha the old 60Hz Routine! (as Inspector Clouseau might well have said) :D Te He!! Your good intentions have been duly noted grooveguy, thanks. By calculation the + 0.002" (0.362" vs 0.360") on the Drive Capstan, and with the DR33C's Platter Measurement being 12.001" Accounts for an "Overspeed" of 0.25RPM from the 1500RPM Synchronous Drive Motor. The regulations covering the U.K.'s Permisible Electricity Supply Frequency Variability are + or - 1% which could cause the Platter to be "Off" by + or - 0.45RPM
Quote " National Grid has a licence obligation to control frequency within the limits specified in the 'Electricity Supply Regulations', i.e. ±1% of nominal system frequency (50.00Hz) save in abnormal or exceptional circumstances" I think therefore, I can just about live with this Small Speed Error
Regards :wink: :P :D Soulbear

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