Revox B77 pinch roller arrow.

[Kentode]

I've just been cleaning the tape path and for the first time l spotted this little arrow on one side of the pinch roller.

I'm going to return it to the roller arm with this side facing out, making the arrow turn towards the take-up reel, but would it really make a difference if l didn't?

[stevehertz]

The arrow must be there for a reason, whether or not it's obvious. I'd place it back on its mounting so that it rotates in the direction of the arrow under normal operating conditions.

[LittleGeoff]

Just looked a my B77 and it has the arrow facing to the take up spool. I also have a non original replacement pinch roller that doesn't have the arrow.

[Kentode]

Agreed, Steve. I don't know if this is the original roller supplied by Studer or an aftermarket replacement, perhaps someone on here may know.

It would be an interesting experiment, for someone with the equipment and skills, to record test tones and check wow and flutter with a roller in both directions.

I suspect that some audio-tom-foolery could be applied in the addition of an extra zero to the cost of a "Directional Rubber" roller!

[Radio Wrangler]

It might not be a matter of which way it rotates, but a reflection of which side should go towards the outside of the machine?

David

[stevehertz]

Originally Posted by Radio Wrangler

It might not be a matter of which way it rotates, but a reflection of which side should go towards the outside of the machine?

David

Yes, are both faces exactly the same or, for example, does the bearing protrude slightly more on one side?

[Kentode]

I'll take it off later this morning and measure it.

If I put it on backwards, will l hear secret messages?

[Ted Kendall]

Studer rubber rollers had this arrow from the late 70s - early A700 rollers didn't, and neither did the green ones, most of which are extinct by now. Perhaps it's to do with all the wear tending in the same direction? I think it coincided with the introduction of blasted capstan shafts. In any case, Studer did nothing without reason...

[Kentode]

That tallies with a date stamp on the chassis of 1979 Ted, so possibly the original supplied.

I've just taken it off and measured it, but it's completely symmetrical so short of cutting it in half I'm none the wiser!

My only surprise is that it's never cropped up before...

[stevehertz]

Originally Posted by Kentode

That tallies with a date stamp on the chassis of 1979 Ted, so possibly the original supplied.

I've just taken it off and measured it, but it's completely symmetrical so short of cutting it in half I'm none the wiser!

My only surprise is that it's never cropped up before...

Probably because people, without question, just fit it as per the arrow and accept it. Maybe the surface of the rubber has a some kind of microscopic nap as a result of the way (direction) that it is turned during manufacture?

[DMcMahon]

Originally Posted by Kentode

My only surprise is that it's never cropped up before...

Yes it is surprising, I have never heard similar before.

I have just watched a YouTube A77 pinch roller replacement video where he says that original rollers can have direction arrow on them.

David

[ricard]

Perhaps the direction doesn't have any significance per se, but having an arrow on the pinch roller at least means that people don't have to waste time wondering which way to mount it. I.e. they kept getting questions from technicians asking if the rollers should be mounted one or the other side up, and the arrow puts an end to the quander.

[Radio Wrangler]

It may also be that wear pattern of the bush might mean that if you had the wheel out, it would be best going back the same way.

David

[Ted Kendall]

Fair point - the load is quite high on B77 capstans - 1.2kg, as opposed to the 1.5kg of early A77s and the valve machines with smooth capstan shafts. The A700, which is a constant linear tension design, can use less pressure, as the capstan is working under more closely controlled conditions. I have had the most awful wow on 4.75/9.5 B77s when the capstan shaft had worn smooth.

[TIMTAPE]

Yes and the A700's controlled tape tension operates on both supply and take up reel sides making it doubly effective compared to A77/B77/PR99 machines with neither. A properly set up A700 can run with much lower pinch roller pressure, resulting in lower wear on capstan shaft and pinch roller bearings. The controlled back tension also results in significantly lower head wear.

[Kentode]

Originally Posted by Ted Kendall

I have had the most awful wow on 4.75/9.5 B77s when the capstan shaft had worn smooth.

Thankfully, l don't have that problem! It seems that I'd have to send it to the antipodes to be refurbished.

[Ted Kendall]

No, that one looks fine, but it's the standard shaft. The low speed shaft is like a panel pin - it's 2/3rds the diameter of the standard shaft, with the tacho frequency changed to get the speed correct. The contact patch is tiny, and wear is a problem. I'm sure somebody over here could do the necessary bead-blasting, but no doubt there would be a learning curve involved.

[Kentode]

Originally Posted by Ted Kendall

I'm sure somebody over here could do the necessary bead-blasting, but no doubt there would be a learning curve involved.

Considering that they sold throughout Europe and Great Britain in large quantities I'm curious as to why someone isn't already offering this service. A nice gap in the market, methinks.

[Michael Maurice]

Wouldn’t you have to put fresh metal on the capstan, then grind it to the required diameter before shotblasting?

I know it’s just a matter of a few microns, but we are talking of something that’s very very precise.

[Radio Wrangler]

With the motor having an analogue servo speed control based on a frequency discriminator it would be fairly trivial to make a slight increase in rpm to correct the speed.

Grit blasting isn't difficult but getting it uniform takes some effort. You'd want to mask off the area not to be blasted, and you'd want the capstan spinning with a wide enough fan of grit to ensure uniform coverage. Do-able in most countries. Finding a Talysurf gauge to check the finish might be problematical, but then a stereo record player cartridge wired for hill-and-dale would make a DIY sensor... outpud should be noise!

David