Revox A77 tape guides modification?

[john_benham]

The later machines have a bearing on the feed side with the appropriate space washers to get the final and correct spacing. I always removed the rigid spacer on the take up side and added an identical bearing with spacer on the take up side. I have forgotten which grade of bearing I used. I think I went from a class 3 to a class 5 for smoother results. Just take your factory bearing or spacer with you to a nut bolt screw and bearing shop and they will get the correct bearing for you.

Thanks for the suggestion except both of my guides are static - the same fixed design. So I don't have the supply side bearing guide to model it from. If I can find a couple of metal circular spacers-inserts, I could go to my local bearing supply house and match the inner and out diameters and width to the specs I need. Then sandwich the bearing between two circular Teflon washers. Fun to try anyway. Thanks again - JB

 

[jlb2]

With 0,3mm total thickness tape may stuck between side plates (proved). This design is not so precise. Flanges are large, fixed and if tape is not perfect you have a problem. 0,4mm is OK. It is important anyway only for left guide. Right should be 0,4 with left you can experiment, but not less than 0,35mm.

It's not my experience really, but you are correct at least that tolerances can interfere and it is important to experiment after changing the shims, before you start playing actual tape. My tape stock and archives are Agfa/BASF through RTM, which strictly conform to the standard 6.25 width.

Tape from other brands may not be slit accurately so I agree that 6.35 mm is safer, at the risk of elevated phase fluctuations, which I have confirmed by measurements. Unlike W&F and scrape flutter this is valid for both the left and right tape guides, since the capstan and pinch roller don't prevent the tape from moving laterally.

This is where the design of the Revox guides is a problem, as they have wide flat stationary flanges, and the precision of the shims is not so great, which forced the designers to make compromises. On better tape transports the guides are fully rotating and diabolo-shaped. Where stationary guides cannot be avoided, they can be very slighly slanted or disposed in such a way that they make the tape remain in permanent contact on one side so they cannot move laterally. Well-designed broadcast machines have both width tolerance and lateral guidance. It also helps playing tapes with splices, which is especially important in broadcast use and with archive tapes.

Unfortunately I don't think it would be realistically feasible to modify the Revox guides in a similar way. Instead I often play the tape from end to beginning at normal speed before the actual play, in such a way that its height on the reel is very slighly lower or higher than normal. Then I turn the tape over and actually play it. This makes the tape remain on one side of the left guide, hence a measurably improved phase fluctuation.