Revox relaped heads

[microstrip]

I am thinking about having the heads of my Revox A700 relaped. As I will use my Revox mainly to listen to the tape project tapes I am very concerned about the possibility that the heads can damage or shorten tape quality. Anybody has experience with Revox relaped heads?

[Ben]

Looks around ... no Ironbut, I guess I will have to fill in. :)
I suspect that if your heads are that bad a shape to damage a
tape of any kind, a head replacement rather than re-lapping might
be a better idea. It all boils down to how many hours the that
heads have been in use. If I remember right from the beginners guides
you can only re-lap once or twice before you need to replace the head.
If your tape path and heads are correctly aligned and *clean* and free
from visable damage I can't off hand see how you could damage tape playback
of any kind.
Ben.

[Tim]

Revox heads have "relief cuts" in them which prevents a groove or channel from forming on the head face as the head wears.  Because of this, they typically don't require re-lapping.   An exception to that is if someone tampered with the head alignment screws in the past, which subsequently created multiple overlapping wear patterns on the head face. This would cause poor head-to-tape contact, resulting in poor playback quality. Check for broken alignment screw paint.

Why do you think the head needs re-lapping?   Is there a problem with playback quality?  Does the wear pattern look good? (a uniform, vertical rectangle)  Can you see the head gaps? (if so, the head is shot)

FYI, the A700 deck has many reoccurring transport problems which result in excessive wow & flutter.  It's something to consider before pouring a lot of money into this unit (new heads, etc.).   

[microstrip]

The heads look nice, the wear pattern is around 3mm but regular and rectangular. Although tape tension is correct and is stable there is some amplitude modulation measured with a 12.5 kHz 0dB tone recorded at 15ips. The flutter spectrum looks quite nice and comparable to the one of my PR99. This A700 is in very good condition and I checked the operation of the tension of arms - the calibration yields the values stated in the service manual. 

[microstrip]

I am now sure that it is an head problem - I replaced the heads with some better condition of a Revox B77 and the amplitude modulation at 12.5 kHz disappeared. The only solution seems to be having the heads relaped - unhappily the good heads are 4 track, useless for the Tapeproject tapes.

[ironbut]

Hi Francisco,

Even when there are relief slots present and the machine was adjusted perfectly, headwear will result in high frequency losses and this could easily be the cause of the 12.5k distortions. No matter how perfectly the tape is traveling across the head, wear will change the shape and flatten the peak of the head profile. The "shinny" square is the total contact area which has been polished by tape friction.
The force that the tape exerts against the head is highest at the gap and decreases the further away the tape gets till it actually looses contact. The tape wrap varies with head design but too much will result in scrape flutter and phase related anomalies.

I wouldn't get too worked up about having to have your heads relapped. I think that JRF charges just under $100 per head and in comparison to getting a nice stylus re-tipped (or fixing anything on a modern auto) that's pretty darn reasonable. For me, the tough part is having my machine down for a whole 2 weeks!

My advice would be to send the headblock to John and have him go over the whole thing and you'll be set for years.

[microstrip]

Many thanks for your advice - after I exchanged some mails with John French the heads were sent to JRF for relaping.

[microstrip]

Just a quick follow-up of my questions. I received today the Revox heads from JFR - they look like new, John also sent a lab report quoting the initial and final tests and an estimated 70% life remaining!