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Vintage Tape (Audio), Cassette, Wire and Magnetic Disc Recorders and Players Open-reel tape recorders, cassette recorders, 8-track players etc.

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Old 4th Apr 2020, 2:01 pm   #1
omerisik
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Default Revox B77 MK II slowing problem

Thanks so much to get me in the community. I wish all of you and the human being overcoming the struggle against the corona virus. I'm a medical doctor (Cardiovascular surgeon) in Istanbul. Recently I've begun in interesting with vintage reel to reel tape recordings and bought some of them from second hand sellers. My problem is, one of my devices (Revox B77 MK II) slows down both while recording and playback when exceeding the half of the reel band. Is there anyone experiencing such a problem and can help me. Thank you.
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Old 4th Apr 2020, 6:17 pm   #2
Michael Maurice
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Default Re: Revox B77 MK II slowing problem

What tape are you using, if its old stock from say the 80's and 90's then it could be suffering from Sticky Shed Syndrome.

What size spools are you using, if 10" ones, try pressing the reel size selector to the small spool position.

If the tape speeds up then the problem is due to the tape.

If you were to rewind the tape and start again, is the speed correct? If it is then again it points to SSS.
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Old 5th Apr 2020, 12:55 am   #3
jamesperrett
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Default Re: Revox B77 MK II slowing problem

I'd agree with Michael - sticky shed is the most common reason for tape slowing down part way through the reel. It is vitally important to thoroughly clean the machine after any tape that has shed as any sticky remains of the tape could cause other tapes to slow down.

However, it is also important to set the tape tension switch to the correct reel size. If you try to play a reel with a very small hub on the large hub setting it will probably slow down towards the end of the reel.
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Old 5th Apr 2020, 3:18 pm   #4
TIMTAPE
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Default Re: Revox B77 MK II slowing problem

Quote:
Originally Posted by omerisik View Post
My problem is, one of my devices (Revox B77 MK II) slows down both while recording and playback when exceeding the half of the reel band. Is there anyone experiencing such a problem and can help me. Thank you.
As already mentioned faulty tapes could be a contributor but if the sound is clear it's likely to be slippage at the capstan shaft/pinch roller. This is a common issue with B77's running at 3.75/7.5IPS or slower. It often only starts to slip in the second half of the reel as you say.

The problem in my experience is normally pinch roller pressure too low, pinch roller rubber gone hard, or the capstan shaft rough finish has been polished smooth. It is often a combination of all three. The pinch roller pressure can be adjusted but a hard pinch roller needs to be replaced and the smooth capstan shaft needs to have the finish roughened by an expert.


Also the B77 is not designed for reels smaller than 7" diameter. A 5" or smaller reel on the left side will probably slow down the tape travel even if everything else is correct. The inside diameter of the reel which must be no smaller than 2 3/8", which is a standard 7" reel.

Hope this helps.

Tim
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Old 5th Apr 2020, 10:59 pm   #5
jamesperrett
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Default Re: Revox B77 MK II slowing problem

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Originally Posted by TIMTAPE View Post
Also the B77 is not designed for reels smaller than 7" diameter. A 5" or smaller reel on the left side will probably slow down the tape travel even if everything else is correct. The inside diameter of the reel which must be no smaller than 2 3/8", which is a standard 7" reel.
While it may not be designed for small hub diameters, I've not found them a problem provided the reel size switch is set to small.
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Old 6th Apr 2020, 12:27 am   #6
TIMTAPE
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Default Re: Revox B77 MK II slowing problem

Yes we might get away without speed issues with a 5" reel or even smaller when played right to the end if it's switched to "small", and the machine is in top mechanical condition.

But the Revox specs (for the 3.75/7.5 IPS models) state:

"Reel size: Up to 10.5" diameter (minimum hub diameter 2.36 inches). Tape tension switchable for small hub diameters." (B77 MkII Service Instructions)

A standard 7" reel has a hub diameter of about 2.36". That's all the performance the machine is guaranteed for.

The 7.5/15IPS model seems to have more leeway in my experience probably because the capstan shaft being of larger diameter presents a larger surface area to grip the tape.
Also in these types of machines, the pinch roller does not drive the tape. It only presses the tape onto the capstan shaft. Whereas in a machine like an Otari MX5050, the pinch roller being much wider than the tape, is itself driven by the shaft and so assists in driving the tape. But on smaller diameter capstan shafts this can damage the tape, hence the pinch roller only touches the tape, not the shaft.

Last edited by TIMTAPE; 6th Apr 2020 at 12:42 am.
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Old 7th Apr 2020, 12:32 am   #7
jamesperrett
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Default Re: Revox B77 MK II slowing problem

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Originally Posted by TIMTAPE View Post
The 7.5/15IPS model seems to have more leeway in my experience probably because the capstan shaft being of larger diameter presents a larger surface area to grip the tape.
That would explain it as my experience is with the high speed version. Single masters occasionally come in on 5" reels.
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Old 7th Apr 2020, 1:13 am   #8
TIMTAPE
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Default Re: Revox B77 MK II slowing problem

Quote:
Originally Posted by jamesperrett View Post
Quote:
Originally Posted by TIMTAPE View Post
The 7.5/15IPS model seems to have more leeway in my experience probably because the capstan shaft being of larger diameter presents a larger surface area to grip the tape.
That would explain it as my experience is with the high speed version. Single masters occasionally come in on 5" reels.
Yes knowing you transfer studio tape recordings I guessed your B77 would be the HS (7.5/15) version with the larger (9mm) shaft dia. My B77 is 3.75/7.5 with the smaller (4.5mm) shaft. My super low speed A77 (15/16 and 1 7/8) has a capstan shaft dia. even smaller than the 3.75/7.5 type (3mm). Towards the end of reels it's even more vulnerable to tape slip so the mechanicals have to be in good condition.
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