Tape Deck Motor Speed

[@Techmoan]

Many thanks for putting this video together. I'll go ahead and swap our the capacitor. My only issue now is finding anyone who can supply a suitable 220v 1uF cap. Any suggestions? Again, this is much appreciated.

[@UberAlphaSirus]

There are plenty on ebay Mat. search for "10x Capacitor 1uf 5% 630V DC Polypropylene Axial Valve Metal Film Audio Audio UK" seller "dunkuk" good price and 10 to select from for best tolerance and therefor speed.

[@Techmoan]

@@UberAlphaSirus Ahh - I take it that’ll make no difference to the result (utterly clueless chap typing).

[@sparkyprojects]

You don't have to find a 220v one, as long as the voltage is higher it's fine. This would be ideal, it's the style my friends use smile.amazon.co.uk/sourcing-map-Metallized-Polypropylene-Capacitors/dp/B07JX5J6RG/

[@Techmoan]

@@sparkyprojects Brilliant, many thanks again.

[@UberAlphaSirus]

@@sparkyprojects 5% ain't to bad. The ones I couldn't figure out to link seem to have pretty decent tolerances. I ediyed my original post as it did make much sence, lol

[@Ravenesque]

Techmoan is right, you are amazing. wow. thank you for the info :)

[@RODALCO2007]

I thought that most of these Akai Reel to reels also changed the drive belt via the mechanical lever of that switch for 50 or 60 Hz.

[@usaf4dbt]

Thank you!

[@andymouse]

Cheers.

[@eDoc2020]

I'm here from Techmoan's new video. I certainly see how changing the capacitor can change the speed on an induction motor running below synchronous speed, but I don't see how a well-regulated speed could be set this way. Wouldn't the load have a huge impact on the speed? And then there's line voltage variations and component tolerances. What am I missing here?

[@dino6627]

It is puzzling. I thought the benefit of using a mains AC motor, usually in older equipment, was that the speed is constant and an electronic speed control was not needed, as with a DC motor. I think the fact that it is a background music system, the speed is not critical and the crude, fan style, capacitor speed reduction is acceptable.

[@eDoc2020]

@@dino6627 Equipment using the AC line for accurate timing use synchronous motors which rotate in sync with the AC line. 3600rpm on 60Hz and 3000rpm on 50Hz. A less regulated speed might be acceptable for a BGM system but the same circuit is used here in a reel-to-reel where standards are higher. There must be some factor I'm not considering which leads to less speed variation.

[@dino6627]

@@eDoc2020 It is strange, if not locked to the AC frequency there doesn't seem any regulation to the speed. It would be interesting to know more about the motor and its windings. I once saw an old video recorder that had a synchronous AC head-drum motor, with an electromagnetic brake to bring it in sync with the video signal. Not what is happening here, but maybe of interest.

[@sparkyprojects]

I'm not an epert, but yeah, you will get some variation, but this system has been working for many years, and is probably not enough variation to notice, even if you record on one device and playback on another

[@eDoc2020]

@@sparkyprojects I was thinking it must be something mechanical helping to regulate the speed. If there's a nonlinear relationship between torque and speed this could mean a given change in power would result in a much smaller change in speed. I recall learning that power lost to air resistance is related to the cube of the velocity. I decided to do the math and sure enough, if you take the ratio going from 0.6 to 1.0 uF (1.667), take the cuberoot and multiply by 50 Hz you end up with 59.28Hz, quite close to 60. Your Akai has a much smaller capacitance ratio of 1.25 but if you square it (since power is often related to current squared) you end up with 58.02 Hz using my earlier math. I'm not sure if those numbers lining up is a coincidence or not. In your fan example the change in speed appeared to be directly proportional to the capacitor value. This would suggest that it might be a coincidence. The specifics of the winding arrangement probably also matter a great deal. It seems to be one of those cases where something which seems like it should have a simple answer is actually much more complex.

[@nethoncho]

Techmoan sent me here

[@sparkyprojects]

welcome :)

[@joligrunlaub3412]

Ok. But what is the reason for the faster spinning? Does this works on asynchronous motors? Synchronous motors like in the newer akai needs to change the pulley.

[@sparkyprojects]

The motors in tape recorders like techmoans are asynchronous. just like most induction motors, there's a certain amount of slip, if you calculate mains fequency against the poles of the motor it should be 750, 1500 or 3000 rpm for 50hz, but it's actually a little bit slower than that.

[@montynorth3009]

Would a resistor in parallel with the capacitor increase the motor speed?

[@sparkyprojects]

Depending on value, i can only think this will slow down charge and discharge of the capacitor as the cycle changes polartiy, not sure if this will speed up or slow down the motor, but probably won't make enough difference to be useful You would also need a properly rated resistor for the current, it's much easier to use capacitors in series and/or parallel to tweak the speed.

[@ttww1590]

3:12 Sparky says the lower capacity capacitor gets disconnected. Techmoan seems to have wired the capacitor in the same spot.

[@sparkyprojects]

Techmoans machine is an either/or, the Akai in my vid adds capacitance to the original, Techmoan did it right.

[@lauraiss1027]

Thank you!