Revox G36 capstan dimension

Aega

New Member
Good afternoon everyone,

Could anyone take and share an exact measurement of the diameter of the capstan zone that drives the tape on a Revox G36 50Hz/240V European version for speeds of 9.5/19cm/s, please?
A full original drawing of such capstan would be cheered at extensively.
Very much appreciated!

Previous owner decided to use abrasive paper to clean the current one and destroyed the active area resulting in a 3% speed loss, which does not play with my original tapes.

My best regards,
Aega
 
For your 50Hz/240V machine, 9.5/19 cm/s speeds, I believe the capstan shaft diameter should be 3.26 mm. This was determined from the links below, which discuss converting a G36 from 9.5/19 cm/s speeds to the high speed version (19/38 cm/s).

As mentioned in the links below, Revox manufactured the high speed version of the G36 at one point by using the original 6/12 pole motor and doubling the diameter of the original capstan shaft (to 7.251 mm). Hence, your capstan should be half that diameter.

I have a G36 myself that I could measure, but I would need to buy or borrow a micrometer. I've never actually used a micrometer, so not sure how accurate my measurement would be. :)

Links:
http://www.diyaudio.com/forums/anal...x-g36-reels-motors-not-working-anymore-3.html
http://tapeproject.com/smf/index.php?topic=665.15

Although not cheap, you should be able to find a replacement capstan shaft (or complete motor) on one of the auction sites. With the exception of getting a machine shop to cut you a new capstan shaft, the next best alternative might be to build/buy an external 240VAC power inverter with variable frequency adjustment. A frequency deviation of 0.5Hz from 50Hz should yield ~1% change in tape speed, according to info in the Revox service manual, so you'd need to be able to deviate at least 1.5Hz in order to get a 3% tape speed change. The G36 motors run synchronous to the AC power frequency, so I'm not aware of any other simple electronic solution for altering the tape speed (but I'm no expert, so maybe someone with more G36 experience knows how it might be done).

Good luck!
 
Thank you very much indeed, Tommy, I shall need to read in the links you sent.
I do not have the G36 with me, a friend is completely overhauling it, but will be looking into all this information and take it from here.
He works for a Mercedes supplier and they will be machining two shafts: a high and a standard speed.
Will revert to you as soon as we have everything up and running.

Very much appreciated, thank you,
Aega
 
I'd be interested in hearing how things turn out.

Hmmmm, newly-machined high speed capstans for a G36 ... sounds like something you might be able to sell to other G36 owners :naughty: LOL
 
I have a G36 that was converted to run on 60 hz; it has the factory retrofit installed in machines exported to the US & Canada. The capstan shaft is thinner than the standard A77 capstan shaft and measures 0.117" to 0.118". This was done with the shaft in the machine and is not easily accessed with a caliper micrometer so don't consider that figure dead accurate. It'll not only get you into the ball park but also into the diamond but not on a base.

I just looked into my G-36 library and found the 60 hz conversion kit instructions and it states the capstan shaft diameter for 60 hz machines is 3.0mm, which is 0.118". That figure will place you on home base. Guess I did better than expected with that caliper.

I did follow the supplied links provided in some comments here and they have been very informative. It seems Studer had several variations of this machine which is understandable considering its age.

It is, however, one helluva nice chunk of eye candy. Viva la toob. :banana:

Robert
 
Thank you for that, Robert!

In the meantime I was given exact measurements by a friend in Germany and had 4 capstan shafts made to order (including heat treatment, hardening, etc) by a local Mercedes supplier of machined components.
Also, as I am planning to experiment with upgrading the G36 to HS, I also ordered 3 capstans to ensure the conversion without major modifications to the equipment. Meaning, the driving section being double in diameter.

The 3.75/7.5 capstans are spot on, they all work flawlessly. The HS conversion ones I still need to test, but I am concerned about the potential drop in contact surface between the tape and the playback head, owing to the fact that the capstan is twice the normal diameter. Will let you know.

G36 works very well, except for one aspect I noticed: towards the end of a 10" tape, the donor reel adds too much resistance and the tape slows down slightly. Any ideas where I should look to solve this issue? I do not own a dynamometer to measure break tension, should I get one?

Thanks for all the good words, my best regards,
Aega
 
Thank you for that, Robert!

In the meantime I was given exact measurements by a friend in Germany and had 4 capstan shafts made to order (including heat treatment, hardening, etc) by a local Mercedes supplier of machined components.
Also, as I am planning to experiment with upgrading the G36 to HS, I also ordered 3 capstans to ensure the conversion without major modifications to the equipment. Meaning, the driving section being double in diameter.

The 3.75/7.5 capstans are spot on, they all work flawlessly. The HS conversion ones I still need to test, but I am concerned about the potential drop in contact surface between the tape and the playback head, owing to the fact that the capstan is twice the normal diameter. Will let you know.

G36 works very well, except for one aspect I noticed: towards the end of a 10" tape, the donor reel adds too much resistance and the tape slows down slightly. Any ideas where I should look to solve this issue? I do not own a dynamometer to measure break tension, should I get one?

Thanks for all the good words, my best regards,
Aega



First of all, may I ask why you are converting this machine to high speed?

Also, I am assuming you have a service manual and some test equipment available.

I made some observations on my G36 regarding the possible lifting of the tape from the playback head. In photo D00085a, notice the wear on the playback head. That wear is wider on the right side of the gap which can be seen. This, I am certain is partially due to the wear on the tape guide to the right of the playback head. Another possibility is a slightly incorrect centering of the playback head with respect to the tape but I'm inclined to doubt that.

Now, assuming the tape guide on your machine is similarly worn. This would cause the point of contact to shift to the right of the gap on the playback head. It is my feeling that by your adding the larger diameter capstan shaft, the tape will restore close to it's original position. The tape may lose contact with the guide's worn surface but will still maintain its vertical position. You just might get lucky. This wouldn't work on an A77 as the small low speed capstan is 0.177", larger than the G36's 0.118". The high speed capstan shaft diameter is 0.356" which will considerably affect tape to playback head contact. The correct procedure to make such a conversion on an A77 is to drill new holes in the aluminum casting so the motor can be repositioned to maintain the correct contact on the playback head.

I've had this G36 for a few years. I bought it essentially to add to a collection of A77's of which I have 6; two are two track high speed. All have new heads which cost me more than the respective machines, not to mention the cost of added electrical and mechanical parts needed to restore them and 2 calibration tapes at $135 each. But, the G36 has yet to be put on the bench. It does work but the switch for the tape tension isn't working properly; it's a mechanical problem. I have a full compliment of new tubes also. I haven't fiddled with it for a couple of years, until now so we're both going to learn something from this experience.

Now, to your end of large reel slowing speed problem. I doubt it's the brakes rubbing as that would very likely cause an uneven speed. What I'm inclined to think is the capstan pinch roll and /or related solenoid. The pinch roll may be hardened and glazed. As the supply reel diameter decreases, the load imposed on the capstan to pinch roll friction is increased. A hardened and glazed roller will lose it's friction. As for the solenoid, ifn the pinch roll to capstan shaft pressure is low, it may cause a uniform slippage which can easily be interpreted as speed slow down. Have you monitored the voltage to that motor prior to and when the problem manifests itself?

That the problem only exists with a 10.5" reel is puzzling. The added weight of the larger reel should have no effect but the smaller diameter of the 7" reel hub just might at the end of the 7" reel, if the pinch roll to capstan shaft friction is compromised. When the problem happens, add a little pressure to the capstan pinch roll arm. That may indicate a pinch roll problem. Another thing to try is manually rotate the supply reel so as to remove the tension on the tape. When doing the latter, it may be necessary to apply a very mild pressure to the tape near or between the left guides to keep it in position, else the tape may skew past the heads and into the capstan/pinch roll contact. Use an expendable tape if you have one.

The service manual gives these tips in section 2.1.3. regarding tape tension. (A) Faulty adjustment of the brake band. (B) Electrical fault in the feed motor (which I assume to be the left reel motor) (C) Electrical fault in the phase shift condenser, C72.

And, I might add that it takes 1.7 kg (3.75 lbs) to pull the capstan pinch roll from the capstan shaft enough to create an audible change in pitch (tone).

Robert
 
For your 50Hz/240V machine, 9.5/19 cm/s speeds, I believe the capstan shaft diameter should be 3.26 mm. This was determined from the links below, which discuss converting a G36 from 9.5/19 cm/s speeds to the high speed version (19/38 cm/s).

As mentioned in the links below, Revox manufactured the high speed version of the G36 at one point by using the original 6/12 pole motor and doubling the diameter of the original capstan shaft (to 7.251 mm). Hence, your capstan should be half that diameter.
Good luck!

I just happened to re-read this thread and realized that the math in my earlier post was rather off, i.e., 7.251 mm / 2 does not equal 3.26 mm!
Looks like I transposed a couple decimal digits there.

To set the record straight, 7.251 mm / 2 = 3.6255 mm.
 
Hello Everybody!
Just made for my G36 new adapter to convert 7,5 ips to 15 ips. Now is necessary to change shematic to make proper EQ for 15 ips speed. Maybe anyone has experience?
 
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