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Reel To Reel All discussions pertaining to reel to reel decks. These include general usage, recording, playback, and service questions. For subjects related to tape itself, see the Open Reel subforum under this one. Obscure service subjects that don't quite fit go in the Help and Do It Yourself subforum.

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  #1  
Old 09-09-2017, 01:01 PM
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TomasL TomasL is offline
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My Revox A77 MKII

Well, bought my self an REVOX A77 MKII (4-track).
It seems to be an original 2-track that has been modified to 4-track
serial is S035056
As it transpired it needs some work done.
The first thing I found out was that the brakes didnt work
No wonder why though, the right hand brakeband was missing.
So I had to get a set of brakes and fit the right hand brake band

So where am I now, well, the adjustment for capstan speed was broken, so I had to get a new capstan speed controller card, and I went for a card with a 555 instead for the Coil version, will get it next week I hope, after that I can continue.
Capstan speed was perfect when iddle, but when tape was loaded and on PLAY, the speed dropped a bit.
Furthermore, I removed the capstan cleaned and re-oiled the sintered bearing.

Then I obviously need some alignment tapes, so I can align it properly and adjust all Electronics.
I hope the heads is not too worn out, maybee someone can tell.

First image shows the missing brake, drum removed.
Second image, since I had a lot of large O-rings, I manufactured a belt for the counter.
Image 3, new brakeband and belt for the counter fitted.
Image 4 Recording head.
Image 5 PB-Head.
Image 6 Erase head.
The last two images shows some rather useful functions on my DMM
Attached Images
File Type: jpg WP_20170826_11_56_52_Pro875.jpg (375.5 KB, 38 views)
File Type: jpg WP_20170826_12_05_28_Pro875.jpg (306.3 KB, 34 views)
File Type: jpg WP_20170826_12_37_10_Pro875.jpg (373.8 KB, 38 views)
File Type: jpg _8277316_875.jpg (386.3 KB, 58 views)
File Type: jpg _8277317_875.jpg (369.8 KB, 58 views)
File Type: jpg _8277318_875.jpg (340.3 KB, 41 views)
File Type: jpg _8317327_875.jpg (477.5 KB, 43 views)
File Type: jpg _8317328_875.jpg (411.6 KB, 39 views)
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  #2  
Old 09-09-2017, 01:11 PM
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Tapetech Tapetech is offline
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Heads are quite worn. Do a full mechanical and electrical refurb and then see what they actually sound like. If no good, then send photos to JRF and get his opinion on doing a relapping service on them.
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  #3  
Old 09-09-2017, 01:45 PM
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What is "Relapping", Heard about it, but havent found any description of what actually is done?
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Old 09-09-2017, 02:10 PM
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Tapetech Tapetech is offline
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It puts an all new surface on the head face. One that is very even and allows the tape to have better contact and better high frequency response. Always best done by a company that specializes in that procedure. Here in the states, it's JRF Magnetics. Go to their website for more info on relapping.

Just a few days ago I worked on a B77 that my customer bought of eBay. The ebay seller told my customer that he fully refurbished the deck, including a head relapping (done by the seller). It was a joke. With my MRL test tape the play response at 10KHz was down 10 dB. The play amp was working perfectly, so the crude head relapping attempt basically ruined the head. It has to be done a very certain way to actually improve the performance of the head. I have sent many old heads to JRF for relapping and they always come back with much better performance. Sometimes heads are too far gone to be replapped and JRF always tells you if that is the case after they do an evaluation.
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Tim@MusicTechnology.com**** WWW.MusicTechnology.com
5418 Port Royal Rd, Springfield, VA 22151,**** 703-764-7005, EXT 107
  #5  
Old 09-09-2017, 02:14 PM
robstan234 robstan234 is offline
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Basically it is the re-shaping of a worn head to a more correct profile without wearing off more head than is possible or widening the heads, if not done properly it will certainly ruin the heads. JRF explain here http://www.jrfmagnetics.com/index.ht...relapping.html
all the best
Rob
  #6  
Old 09-09-2017, 02:37 PM
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Anyone in Europe that do the same job?
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  #7  
Old 09-09-2017, 02:47 PM
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Don't know, but I'm sure there are. Go to some European tape forums and ask.
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Tim@MusicTechnology.com**** WWW.MusicTechnology.com
5418 Port Royal Rd, Springfield, VA 22151,**** 703-764-7005, EXT 107
  #8  
Old 09-09-2017, 02:50 PM
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well, sofar, this is the only r2r forum I have found.
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  #9  
Old 09-09-2017, 03:49 PM
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So, if understand this "ReLapping" correctly, it is to grind/polish down the heads so all angles is correct.
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  #10  
Old 09-09-2017, 05:42 PM
earczar earczar is offline
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Thats right
  #11  
Old 09-09-2017, 09:01 PM
Audiomayvin Audiomayvin is offline
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Hi!
If I had my druthers, I would tell you to find new-used heads on E-Bay because your heads are the old version. The more recent version has horizontal slits and is considered to be a superior head. The part # is the same.
All the best,
Leon(The Audiomayvin, Montreal (514)739-5403)
  #12  
Old 09-09-2017, 09:53 PM
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Yes, you could buy used heads on eBay, but that would only make sense if they had a lot less wear than the ones you have now. And you would have to get those relapped as well.
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Tim@MusicTechnology.com**** WWW.MusicTechnology.com
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  #13  
Old 09-10-2017, 12:52 AM
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So, A thought, could G36 heads be used? or B77.
they seems to be available as NOS
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Old 09-10-2017, 01:31 AM
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You could use B77 heads, but not G36.
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Tim@MusicTechnology.com**** WWW.MusicTechnology.com
5418 Port Royal Rd, Springfield, VA 22151,**** 703-764-7005, EXT 107
  #15  
Old 09-21-2017, 03:48 PM
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So, I finally got it working, after replacing the capstan controller card.
So-far I have found out that the lefthand reel brake needs to be tightned up, since it doesnt stopp the reel quick enough when fast forwarding.

Also, the "tape chock absorber" (whatever it is called), the springloaded pin next to the left tapeguide needs to be dismanteled and cleaned up since it is a Little bit sticky.

Why was the left tapeguide replaced with a bearing, and why not the right-hand one?
Anyone that has a clue?

I have also ordered an alignment tape, so I can at least check how it performes, and if it needs any adjustments.
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  #16  
Old 09-21-2017, 04:23 PM
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Quote:
Originally Posted by TomasL View Post
Also, the "tape chock absorber" (whatever it is called), the springloaded pin next to the left tapeguide needs to be dismanteled and cleaned up since it is a Little bit sticky.
Careful what you do to it! It is supposed to be what you maybe call 'sticky', that is viscous damping. If you do clean out the silicone oil, you need to replace it with 500,000 Centipoise oil again, and that is not easy to come by.

Quote:
Why was the left tapeguide replaced with a bearing, and why not the right-hand one?
Anyone that has a clue?
To minimise scrape flutter. On the right hand side it is unnnecessary so a waste of money, and occasionally makes fast winding pancakes a little less tidy.
  #17  
Old 09-21-2017, 04:33 PM
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Ok, I suppose that when no tape is loaded it should be in the "top".
WHen loading small tapes, or when there is say some 20mm radious of tape left on the spool, the tape does not touch the damper, i.e it has no function.
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Old 09-21-2017, 07:06 PM
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steerpike steerpike is offline
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As in this picture:


You should still have the damping arm just reaching the tape, even when a small reel is used (7 inch reel).
Smaller than 7 inch reels (5 inch, 3 inch) are not appropriate for the B77, it will not work reliably with them.
  #19  
Old 09-21-2017, 11:30 PM
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in the Picture it is in the upper end of the slot, on mine it is in the center of the slot.
If I move it manually to the top of the slot it resets to some 2-3 mm from the top of the slot.
If I move it manually to the bottom of the slot, it resets to the middle of the slot.
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  #20  
Old 09-22-2017, 03:22 PM
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Quote:
Originally Posted by TomasL View Post
in the Picture it is in the upper end of the slot, on mine it is in the center of the slot.
If I move it manually to the top of the slot it resets to some 2-3 mm from the top of the slot.
If I move it manually to the bottom of the slot, it resets to the middle of the slot.
That is not correct; it will need repair.
It is possible the spring is stretched, or has slipped out of place.
Or possibly the bush with the silicone oil is dirty and binding. That is a little more tricky to repair, but not too difficult. Don't remove all the sticky oil when you take it apart.

It should not touch the top of the slot or you will get an annoying tapping noise during fast wind. There are steel end-stops that you can bend toadjust this.

The B77 damper arm does not have an air dashpot as in the PR99, but rather silicone oil in the bush/sleeve.

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