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Author Topic: The best reel to reel Revox transport  (Read 15779 times)

Offline Tim

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Re: The best reel to reel Revox transport
« Reply #15 on: July 17, 2009, 11:22:44 PM »
I've run into two recurring W&F defects while servicing B77/PR99 transports.  I don't know, however, if either applies to the problems you are having with your PR99.

1. The capstan shafts (part that contacts the tape) were "frosted" at the factory.  Perhaps "sand blasted" or acid treated somehow.  I'm guessing it was for better grip to the tape.  Anyway, after only about a year or two of regular use, this frosting became polished-looking.  I started to get many Revox units in for repair with excessive W&F and tape slip (tape slip is how much the absolute speed drops from beginning to end of the reel). This defect was most apparent  towards the end of the reel. I traced it down to the capstan shaft "polishing".  Putting in a new shaft repaired the problem.  Years later I experimented with sandblasting the shafts and also acid-etching the shafts in order to restore the "grip".
 
2. Line-frequency related flutter:  If you lightly put your finger on the reel motor as it was turning in play mode, you could feel the motor housing vibrating at 60Hz.  You could also feel this vibration on the tape and it would be introduced as a flutter into the audio.  I believe I traced it down to a defect motor control Triac.  It was so long ago that I can't remember if that was it for sure.  Anyway, I saw that defect several times.

As far as evaluating any deck for flutter, wow, tape-slip or absolute speed, the only accurate method is to play back a high-quality speed/flutter test tape.  (MRL is the best source for such tapes).  If you record a tone on a deck and then analyze the playback of that same tone on the same deck you will obtain erroneous results.  The reading can be as much as double the actual W&F, or close to zero, or anywhere in between. You also need a W&F meter that has the same standards used by the tape deck manufacture.  In the case of Revox, you need the capability of measuring the peak DIN weighted W&F. That's the only way to determine if your deck is performing normally or is in fact defective.  If your Revox measures less than .06% peak DIN weighted, then it's fine and no repairs are needed.  If your deck measures .12% peak DIN weighted, then your deck is malfunctioning.  Without a proper test tape and flutter meter, you can't know that for sure.  Analyzing the sidebands of a test-tone (especially tones recorded on the same deck) does not answer the most important question: is my deck operating normally or is it defective?
« Last Edit: July 18, 2009, 12:59:02 PM by timlein »
Tim Leinbaugh
Service Technician
with RTR specialty.