Revox A77 repairs

[TIMTAPE]

Yes erase heads were usually made of ferrite which was very hard but suffered from a crumbling as bits of ferrite came away, usually at the gap edges first. I've not heard about this shredding tape though.

A more likely explanation, assuming there's no SSS is worn record and/ or play heads. The slightest bit of tape shed can be enough to lift the tape off the head gap of a worn head.
The whole tape path should be checked for wear and alignment with special attention to the record and play heads. Worn heads on this model will show a wide flat section worn by the tape where in a new condition the heads will show a rounded condition with no flat.

Another possible cause is the tape stock's width. You mentioned RMGI tape. There have been long discussions on other forums about this. Apparently Ampex/Quantegy had put out in the past tape stock that was slightly narrower than the standard. This was fine in itself but after many tape passes a groove of this width was worn in heads and guides. RMGI was criticised for issuing stock that was slightly wider than this but still within the manufacturing tolerance. A machine with old wear grooves would shred the edges of the slightly wider RMGI tape. This is not to be confused with SSS or LOL.
I believe the standard solution is a good tape path with no wear grooves on guides or heads.

Cheers Tim

[jamesperrett]

Revox's (or the B77 at least) tend to be more tolerant of varying tape width as their record and play heads have small grooves above and below the active area of the head which means that the very edge of the tape is not in contact with the head at all.

This varying tape width can be a big problem with other tape machines though.

Cheers

James.

[labcoat man]

Thanks TimTape and James for your very helpful responses.

Ive been meaning to get a relap on these heads, I guess because the high end response seems ok I've been assuming the heads are holding up and have been waiting for a convenient break to send them off. The flat section is there no doubt about it and is at the borderline width of a worn head.

Will get this attended to asap me thinks! Will try a fresh reel, and look at loosening tension (maybe by switching to the small reel setting...) and see if that helps as a stop gap, I have a spare parts machine and will send those heads of for a relap. Meanwhile hopefully cleaning thoroughly between every pass will do the job of getting the next few songs down and mastered.

Interesting about the RMG tape width. I recall observing that tape was getting a bit shaved at the edge of the erase head, possibly then being dragged in powdered form to the record head. Playback seems ok once a good record pass is put down.

Was considering quickly trying to replace the erase head with a spare in the hope that the spare has a smooth surface , but wondering if there is alot of complicated electronic alignment involved with that? If its as simple as popping it in then that would be worth a shot in the meantime.

Tim