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Measuring Back-Tension without a Torque Cassette


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#1 thinkchronicity

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Posted 01 November 2019 - 09:42 AM

Here's a method that works without having to spend oodles on those admittedly very nifty torque cassettes that pop up on ebay. I had one that does play/FF torque only, so didn't want to spend again to be able to measure BT too. I'm not sure how many boomboxes even have tape back-tension tbh. Only one of my five exhibits it.

So you'll need a spare hub and a piece of tape to go on the perimeter to cover the outer slot where the tape used to affix. That will keep your gauge tip from jumping out. And a Correx gauge 0-15gramm. Mine only cost £4.99 from ebay as it had a few cosmetic issues being old and that. Then just place the hub on the supply spindle, press play to create the right operating conditions, orient the hub slot to bottom and carefully employ the gauge tip force horizontally to the right till the spindle turns a bit. The gauge then has a maximum indicator that you can read at your leisure. The slot happens to be exactly 1cm from the centre axis, so the reading will be in gm-cm in this case. Very handy :yes:

The reading might be very slightly out compared to measuring the true 'slipping' tension, but I think with such small forces involved it's pretty negligible. Torque cassettes give a wobbly reading anyway.

Out of interest, has anyone modified their decks to create some back-tension and improved w& f? Yep, I'm a tapehead! love it.

 

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#2 hopey

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Posted 14 November 2019 - 05:23 PM

That's a lot of trouble to go to but it makes sense. With old decks I just work on getting them to perform well as considering the age and the Service Techniques don't hold up overtime.

I find the true test of a Tape deck is the Auto Stop as this is where the tension reaches maximum and confirms the traction for all belts and pinch rollers.

To get the lowest W&F the belts must be correct and the motor has be in good order.

#3 thinkchronicity

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Posted 15 November 2019 - 11:32 AM

Good point and with you there - after 35 years or more it's like auto creak..to a stop if you're lucky.
Belts have to be a high quality consistent mix throughout the loop they say.
Pinch roller's crucial as well for w&f(for any newbies).


That's a lot of trouble to go to but it makes sense. With old decks I just work on getting them to perform well as considering the age and the Service Techniques don't hold up overtime.
I find the true test of a Tape deck is the Auto Stop as this is where the tension reaches maximum and confirms the traction for all belts and pinch rollers.
To get the lowest W&F the belts must be correct and the motor has be in good order.



#4 Jorge

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Posted 15 November 2019 - 01:59 PM

THINKCHRONICITY, thank you! Looks like a nifty trick, I must try this! It was Only while restoring my Nak LX-3 that I realized that for the “proper” rejuvenation these torque cassettes are needed and I gave up on playing with hi-end decks. Cheaper to send to Willy Hermann than buying the set...

#5 thinkchronicity

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Posted 15 November 2019 - 02:25 PM

THINKCHRONICITY, thank you! Looks like a nifty trick, I must try this! It was Only while restoring my Nak LX-3 that I realized that for the “proper” rejuvenation these torque cassettes are needed and I gave up on playing with hi-end decks. Cheaper to send to Willy Hermann than buying the set...


You're welcome! There's a method for doing the play torque too if you get a 0-100gm Correx. Use a spare hub again, with a few cm of cassette tape fixed to it at one end as normal. Then maybe glue or even tie a little loop at the dangling end to go around the gauge tip. Get your perpendiculars in order and that should work. I found a drawing of this cumbersome method in Walter Salm's Cassette Tape Recorders 1973, so not making this up..

#6 Jorge

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Posted 15 November 2019 - 02:48 PM

1973, this must be before torque cassettes became available? Or maybe they never been available for sale? I read somewhere that Nakamichi offered recalibration/(service?) for free to the users

#7 thinkchronicity

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Posted 15 November 2019 - 03:16 PM

1973, this must be before torque cassettes became available? Or maybe they never been available for sale? I read somewhere that Nakamichi offered recalibration/(service?) for free to the users

In his book he shows a pic of a Sansui torque cassette saying this is the easiest method, but it's a more basic design to the modern ones - looks like a horizontal straight spring gauge gets pulled by a piece of tape.
Free servicing? Wow, those were the days if they did.

#8 caution

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Posted 15 November 2019 - 05:45 PM

I find the true test of a Tape deck is the Auto Stop as this is where the tension reaches maximum and confirms the traction for all belts and pinch rollers.

 

How do you check tension on logic decks? Their auto-stop relies on a sensor looking for movement.



#9 hopey

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Posted 17 November 2019 - 05:37 PM

while these can be measured they can't be adjusted other than replacing the belt, pinch rollers and or clutch.

 

Logic decks with optical pickup you would have to bypass the optics to keep it turning or if auto stop works its all sweet as with duel capstan relies on the correct tension with one main belt.