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
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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