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In Reply to: RE: Lapping RTR tape heads and aligning them posted by jtkarma on September 27, 2007 at 11:19:24
Hi, jtkarma:
Believe it or not, I have actually relapped heads in a ReVox A-77 and even done this in an old Advent 201 cassette deck.
This is NOT rocket-science.
It requires unsoldering the head housing, removal of the head from the shield and very careful steps when WET sanding against a piece of crokus cloth laying on top of a sheet of plate glass. It is important to keep the back and forth grinding strokes even at all times and rocking back and forth as you proceed.
There is information on the subject on the web somewhere.
The most important aspect is to constantly inspect the progress and not go too deep. Polishing can be done in various ways, including the use of various forms of metal polishing rouge or even the use of common toothpaste against a fabric surface on the same piece of plate glass.
Reinstall the head in its hum shield casing, re-attech the electrical connections with an UNMAGNETIZED screwdriver and then perform a complete realignment.
When ReVox tape recorder heads got to be more than $100 each, it was normal for technicians to do a relapping. Unfortunately, if the heads were deeply worn or profoundly flat across the gap, it was often impossible to adequately relap one to "as new" condition. There was only so much gap depth left on those heads.
Compare this with standard "deep-gap" heads used by AMPEX on their pro machines! You could relap those many times and still have enough gap depth left for the future.
I often wonder why people are so mystified by something which is so theoretically simple to begin with.
Just my opinion, naturally, but I have BEEN THERE.
Richard Links
Berkeley, CA
Follow Ups:
Richard,
I wasn't really 'mystified' by the prospect, but was wondering how you could keep tolerances even, doing this 'by hand'. In your description for example-a little too much rolling on one side would render and uneven head in theory-we're talking about 'by hand' here. Obviously from what you said, it can't be that critical. I can think of a dozen ways, including a Dremel tool to get those heads perfect smooth again, but I hesitate at the prospect. How do you know when you've gone too deep, does the glass-like surface give way to something more raw?
Kevin
Hi, shoeihell:
No offense, but if you do not believe me, just have a professional head relapping service do your work. This take a certain amount of experience but as I said before, you can certainly do the work if you are careful.
Get a copy of Tape Op magazine (look for it on the web) and check out the ads. You will have to remove the heads from the machine and send them off for relapping service and then hire someone to correctly adjust for Zenith, Azimuth and overall alignment.
You should obtain better results than what you think will happen if you undertake this process by-hand.
Those are my recommendations.
Richard Links
Berkeley, CA
Richard,
No I absolutely believe you. You tape R2R guys have forgotten more about this medium than I will probably ever know. I'm never going to get the opportunity to spend time in an analog studio and hang out with sound engineers etc. It just blows my mind that this has been done so much in the past and I missed reading anything about it. Plus I was born & raised in MO so it really is a "Show me" issue.;-)
The tech who is restoring my Tandberg 9242XD, said the heads were about 15-20% worn. There was a guy briefly on ebay who claimed to have bought a huge existing, OEM Tandberg part's stock somewhere. He was trying to justify some quotient about prices then and prices now. I never really got solid answers because he was phishing to see how much I would be willing to pay. He's playing with the wrong partner, because I don't have the discretionary income to play 'dueling dollars'. I may look up my heads by part# and just ask if he has them and HOW much, period.
Kevin
This should be fun.
I'm a little concerned about having to do the alignment later but I'll cross that bridge when I come to it.
Let's go lapping!
Hi, jtkarma:
Just read up on the procedure and be very careful when you do the work. Better yet, see if you can scrounce some sample heads from a clunker before you do the REAL VALUABLE ones, that is, the ones from YOUR OWN MACHINE!
Good luck!
Richard Links
Berkeley, CA
A couple of important things to keep in mind are that the inductance of the head drops with wear, which is not retrievable by lapping; and that contour and tip depth consistency of the head must be kept as close to original as possible to preserve the designed alignment of the moving tape over the head. Also, none of this means diddly if the rest of the machine isn't in top shape.
I'd say give it a try for sure. What have you got to loose? You may want to go ahead and buy a replacement head just for the sake of having a reference to see how your lapping job came out.
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