How to soften harded pinch rollers? (+ worn tape heads)

[C.B. - Boudio]

I have now got two Revox's, a D36 and a F36. The D36 misses a bias coil core and isn't adjusted, so the recordings are not as good as they could be (still quite good for playback, a very nice preamp or maybe an echo for instruments), and the F36 (latest piece of equipment) seems fine after replacing the burnt-out components in the motor circuit.

But they both have one problem: the pinch rollers are almost as hard as the plastic faceplate, which results in some flutter. The capstans and capstan motors seem to be fine.

On one of them, the D36, I tried the Lenor-method (just a wash softener, repeatedly applied to the rotating roller) - and I will continue it, but it hasn't helped (yet?). Maybe it works better with natural rubber; in my case, it is a green-greyish synthetic rubber (I don't know the name).

Is there anything else recommended?

I know, there are new pinch rollers being made, but the website is Australian (shipping!) and too expensive for me and for what I paid for the machines (I got the F for free and the D for next to nothing).

Apart from that, the tape heads are quite worn. Has anyone here experience with twisting them slightly (to vary the angle of the tape on the head and thus render a better contact)?

I am curious for the cures!

 

[capacitor]

I have no experience with pinch rollers and this product, but there's an automotive seal/rubber softener called AT-205 that might work. I wouldn't use it on anything irreplaceable or expensive without testing it out first, but in a pinch (har) you might consider trying it. One trick with natural rubber is using wintergreen oil. Just pointing these out while someone with specific pinch roller experience chimes in

 

[radardoug]

Get new rollers. As to the heads, if they are worn, they need replacing.

 

[Gold]

Get new rollers. As to the heads, if they are worn, they need replacing.

Those green ones go sticky pretty easily. I’d say get a new pinch roller too.

Try a glass cleaner on the green ones. The black natural rubber ones can be reconditioned with naptha. They can take a light cleaning with isopropyl.

 

[thomasdf]

Pinch rollers from Nagravox are high quality and not that expensive if you consider the cost and quality of such tapes recorders. I'd go that way.
I would suggest to change the motor caps, too, and rebuild the power supply with modern rectifier and new caps. This will help the overall sound and flutter too.

Edit : I want to buy some parts from Nagravox during the summer for my A80. Maybe we can split shipping, even though it's not a deal breaker for me.

 

[C.B. - Boudio]

The problem with replacing heads is to find them. They are (just like the A and B77's and all Revox/Studer-machines) relatively soft. And they aren't made anymore in decades...

I have already changed the capstan motor capacitor in the D36, and that didn't improve hearably (I haven't got a calibration tape at hand, but I think I know someone who may have something). Since I almost exclusively use 18 cm spools, I think I'll reduce the back tension. Or will that make it even worse?

The glass cleaner sounds interesting. Is it window cleaner, then?

@thomasdf Thank you for the offer! By then, I'll definitely know what to do (or maybe it'll be done already).

In the D, the smoothing caps are already changed, but the originals were still good enough (no hearable difference at least). I'm hesitant to swap out its rectifier, because its transformer hasn't got a 240V tap (the F does, but I've only got that recorder since yesterday and I haven't put power on it yet) and with a new rectifier, the high voltage could get too high (line is around 235).

 

[RoadrunnerOZ]

Once the rubber hardens the tape is not gripped properly and the pinch roller surface either side of the tape is held away from the capstan by the thickness of the tape. The hardening of the material will cause this to occur, the rubber needs to compress to make the roller engage the capstan for drive either side of the tape as well as being soft enough to grip the tape, once glazed, grip is lost - the tape alone engaging the capstan will just strip the tape thin - same as incorrect pinch roller pressure. Sounds like the ones you have are synthetic rubber and over time both synthetic and natural rubber dry out and the bonds break down that hold the molecules together - the rubber becomes brittle and you can end up with cracks. If there’s any signs of cracking then new rollers are needed. You can soften natural rubber with alcohol/oil of wintergreen but the oil may cause irreversible distortion of shape (and also damage the tape). Not sure what it would do to synthetic rubber.
With surface hardening you can get past the hard outer skin if it’s not too far gone by stripping the surface rubber with 1500-2500 grit paper but you need to spin the roller while holding the paper evenly against the surface of the roller which means engaging the capstan with no tape present. Band-Aid fix as the rubber may continue to glaze and harden or if it’s already badly perished may lose chunks.
Worn tape heads - there used to be people who re-lapped worn heads, some still around like Nagravox. Depends on cost whether to re-lap or replace but finding NOS Revox could be difficult - Nagravox do have these available but they’re expensive. There is no positioning fix for worn heads.
If the rectifier is replaced with silicon for the original selenium there need to be dropper resistors I believe.

 

[MagnetoSound]

I agree that shipping from Nagravox is prohibitive.

I have bought Chinese made pinch rollers for my machines (B67, B77, PR99) from an eBay seller in Germany and been very happy with them.

 

[RoadrunnerOZ]

I don’t think there are Chinese rollers for the Revox 36 series

 

[Barry Hufker]

Have you contacted the people here? http://www.hilpert-audio.de/audio/i...le&inhalt=ersatzteile/e_ersatzteile_titel.htm
or here https://www.revox-online.de/en-gb/revox-studer-a77

 

[RoadrunnerOZ]

Not sure either of them have for the D36 - F36
Edit: worth an email

 

[Brian Roth]

I've been a subscriber to the Ampex mailing list for well over two decades. More than a few list members have used this company to restore ancient Ampex pinch rollers:

https://www.terrysrubberrollers.com/

Bri

 

[RoadrunnerOZ]

I think OP is in Belgium. There might be someone closer to home - there used to be an outfit in Sweden but I am doing an Akai M9 at the moment and the owner got his rollers re-rubbered in the UK I think - I’ll try and find out from him.

 

[C.B. - Boudio]

@RoadrunnerOZ I have sent Revox-Online an email, we'll see.

I'll try also the glass cleaner, or find someon with a lathe and fine sandpaper (that won't be a problem), for the time being, because they both were so cheap.

As far as the heads are concerned, I have found used G36 heads (which should be the same as the F36, the G has the same electronics), but they don't look too overwhelmingly fresh either.


(these are not mine, these are the ones that are being sold)

 

[RoadrunnerOZ]

Look badly worn

I'll try also the glass cleaner, or find someon with a lathe and fine sandpaper (that won't be a problem), for the time being, because they both were so cheap.

You can do the sanding in place without a lathe as long as you have a vacuum cleaner running or mask off the undersides of the pinch roller location - you just run the machine in play with no tape so the pinch roller is engaged - you’ll need to trip the tape sensor - glue the sandpaper to a flat stick like an ice-cream stick and hold it flat against the roller (wrap it round the back of the stick and overlap it so it doesn’t flick off - you may want to start with 1000 grit if the 1500 doesn’t cut and work up to 2500 - it takes a fair bit of pressure to get the surface sanded but fine grit paper doesn’t remove a lot of product so it’s fairly forgiving - you just need to unclog the paper with compressed air or replace the paper as you go. The surface can be prepared using a damp cloth over a fingertip and a lot of rub pressure to start the process - you have the roller being driven while doing this holding the cloth hard against the roller as it turns - alcohol and water (like window cleaner) also works just don’t use too much alcohol or neat alcohol as this also dries out rubber. I’ve cleaned a lot of pinch rollers this way. Try not to hit the capstan with the sandpaper.

 

[Tubetec]

I've used light Emery paper to recondition pinch rollers too,
I found it best to double sided tape the sand paper to a small square block of timber , then sit that on the top plate and move in towards the pinch ,carefully keeping everything flat and level ,
Definately a good plan to have the hoover running nearby to suck up any debris .

Its probably worth a shot trying to re-lap the heads you have , its not rocket science ,but there is a methodology to it , your not removing material from the vicinity of the magnetic gap , your just polishing out the grooves that have formed either side ,

 

[RoadrunnerOZ]

The wear of tape causes the face of the head to get a flat worn into it in the line of tape travel with sharp edges - the idea is to remove the ridges above and below the tape edge lines and then on to reprofile the head to a curve so the tape runs smoothly close to the pole gaps in the heads again and more importantly that from top to bottom of the head (at right angles to tape edges) the surface line is dead straight - wear from higher speed tapes is common and the edges of the tape can cut in more than the centre forming a bowed surface which results in lack of surface contact area at the pole gaps. Online there are a few DIY guides annd videos around on doing it yourself but you need to have all the bits to do it and also be prepared to do a full head alignment afterwards.
Example guide:
https://www.leson.org/how-to-relap-tape-heads/

 

[C.B. - Boudio]

Thank you for the ideas! I will try with alcohol and with sandpaper if needed as soon as possible.

For the heads: I got the idea of turning the heads here:
https://tapedeckforum.nl/index.php?topic=2227.0
It's all in Dutch (and I'm afraid most of you won't understand much) but I'll summarize.



New head (kop)/maximal pressure - worn head/contact surface


Lapped head/contact surface


- surface turned away


Head turned the other way around - head again worn


Third chance for the head/head straight again.

This over a long periode of time of course.

So, that's why I talked about turning the heads.

 

[RoadrunnerOZ]

Thank you for the ideas! I will try with alcohol and with sandpaper if needed as soon as possible.

For the heads: I got the idea of turning the heads here:
https://tapedeckforum.nl/index.php?topic=2227.0

This over a long periode of time of course.

So, that's why I talked about turning the heads.

Turning the heads is only workable when you’ve had the heads lapped by that method from what I understand?? Turning your heads that are worn (and unlapped with the shown profile) to that particular position will just scrape the leading or trailing sharpened wear edge along the tape scraping off oxide and lifting the tape head centre pole gap away from the tape.
Normal relap - note the sharp wear edges:

The surface of the heads as new have a smooth radius as the tape doesn’t run dead flat across the pole gap but is wrapped around either side for a few degrees - this ensures no irregular turbulent airflow between the head face and tape and a spread load surface area - any sudden profile changes in the head face can cause the tape to lift or flutter away due to sudden air pressure increases. Relap gives a new curved surface - from what those diagrams you posted and the web link are implying and from the translated text it would seem you need that specific lap profile you showed, which is different to normal lapping, for head turning to be of any use.
Edit: ps don’t use pure alcohol as it will further dry out the rubber

 

[RuudNL]

I'm glad that when I bought my Revox A77's in 1975, I immediately bought a spare recording and playback head. They are still in the original plastic bag they came in. Until now I didn't feel the need to replace them.
(And no, I am not selling them! )