Tapesonic 70-T capstan motor

[Deleted User]

As promised here's an update. Two significant problems dealing with the tape transport that needed to be solved. The first was a lack of sufficient tape tension on the take up reel table when playing a 7" tape near the end. What would happen is that when the tape was near the end there wasn't enough torque with the take up motor to keep the tape flowing. The tape would droop and the auto-shutoff lever would engage. I first suspected the motor's drive capacitor which I had replaced, I went with a slightly higher value to increase the torque of the motor. This helped a bit, but not enough. Next I tried dropping the value of the resistor that lowers the voltage to the take up motor so there would be greater voltage delivered to the motor. Here again some change but not enough to make a difference. This is when I checked with a tape guru friend who is very well known. He suggested I take out the Bodine AC motor and take it apart and clean the bearings. I took the motor apart and using a hot air gun I cleaned the sintered bronze bearings and lubricated and cleaned everything I could. Back in the deck and now everything worked the way it should. I had to return the original capacitor and dropping resistor and then do the other motor.

[Deleted User]

The second problem had to do with unacceptable wow and flutter, or speed error. If the speed of the tape isn't kept constant at 7.5" per second as it passes over the playback head gap the music will be changed. If the error happens at a slow rate it's called wow and if it happens at a faster rate it's called flutter. In looking at what Premier Electronics (the builder of the Tapesonic) specified it should be less than 0.12%. They didn't specify which measuring method or what amount is wow and what amount is flutter. They way I used to measure was to first record a constant 3.0kHz tone on the left channel for several minutes. I have a Tenma wow and flutter meter that has a builtin signal generator. I measured an unweighted combination of W/F as 0.45% with wow at 0.15% and flutter at 0.45%. Way too high, music would have a "sour" quality to it, a feeling that sustained musical notes were not staying on pitch. This would be especially noticeable on piano and violin passages.
After very looking at how the rubber pinch roller came down and touched the capstan shaft I saw that there was a distinct gap at one end compared to the other. The pinch roller wasn't contacting the capstan shaft evenly. Exactly as a car wheel having excessive camber not touching the road correctly. Eventually I figured out the problem was caused by the supporting arm that grips the pinch roller solenoid and holds the axis for the rubber pinch roller arm. Whoever made the original part hadn't drilled the hole for the arm grip at 90 degrees to the arm itself.
I found a local machine shop who knew exactly what to do and he made a brand new arm (which you can see in the photo) and now the pinch roller meets the capstan shaft exactly as it should. The flutter now measures 0.07% and the wow is 0.1% considerably better.

[Deleted User]

There were other niggling problems, not being able to put the deck in the record mode. This was traced to an unattached ground wire in the transport to electronics cable. Some sporadic humming. All of these normal audiophile troubles we all figure out.
But, now that things are working as it should, how does it sound? Believe me I try and be as objective as possible (yea, right!). But I believe it is sounding amazing. I don't know if it's due to the improved power supply or better parts throughout. Or maybe the Cardas internal cabling or a combination but playing a particular tape that I recorded decades ago and have listened to dozens of times (The Crusaders) on many different machines, but it was significantly richer harmonically and superb bass quality. I've used a Danish sourced playback calibration tape to carefully adjust the playback response and it's very uniform. I've let the electronics power on for a couple of days and will do some more listening. Couldn't be happier!

dromunds

Outstanding!

[Deleted User]

Thanks! I was just going through all the various papers and schematics I've collected for this project and found the original check out sheet for this deck. It had all the final adjustments made and checked off, the date was February 23, 1970. So, its been almost exactly 49 years since it was originally built.