Vintage rubber/cloth belts?

[John Berard]

I recently picked up a 1960 Stromberg Carlson PR-500 suspended dual motor turntable. I have been researching the model and found an advertisement that says it uses a "impregnated belt". I can't find any info searching this term but have found some information regarding 2 ply rubber/cloth belts. There was also some reference to Rek-O-Kut and this type of belt also used on older tape units.

Can anyone add to this topic?

 

[eiraved]

Impregnated belt usually only means a fabric belt impregnated with rubber.
I've heard that early Ampex recorders used a fabric belt. They used bra-strap material because they couldn't find anyone set up to weave a belt with the dimensions they needed.

 

[Nat]

Gray turntables used a fabric belt with some greenish rubberizing. I bought a belt for a Gray I was given, back in 1974 or 5. Wasn't hard to find, though I can't remember where I got it. Suspect they are not so common nowadays.

 

[bimasta]

I had such a belt, on a Rek O Kut. The fabric weave prevented stretching, and the rubber surface prevented slippage. I wish they made them today.

Bra-strap material? I doubt it — I bought it in the '60s and girls were burning bras.

 

[Nat]

Well, they light drag racer's tire on fire to improve adhesion, so maybe you should try burning your bra strap belt for better grip on the pulley and platter.

 

[John Berard]

Impregnated belt usually only means a fabric belt impregnated with rubber.
I've heard that early Ampex recorders used a fabric belt.

I would agree after looking around some more. Today it would fall into a category called 'Power Transmission Belt'.

Gray turntables used a fabric belt with some greenish rubberizing. I bought a belt for a Gray I was given, back in 1974 or 5. Wasn't hard to find, though I can't remember where I got it. Suspect they are not so common nowadays.

I finally found some pictures of what you describe. But absolutely no luck finding a source yet.

I had such a belt, on a Rek O Kut. The fabric weave prevented stretching, and the rubber surface prevented slippage. I wish they made them today.

Me too. No luck yet finding an exact match. But I did find that McMaster Carr will custom make belts but instead of fabric, they use a mylar sandwitched between layers. I don't think that would stretch enough.

Well, they light drag racer's tire on fire to improve adhesion, so maybe you should try burning your bra strap belt for better grip on the pulley and platter.

lol

 

[BillWojo]

If the belt has threads or cords running the length of the belt it will stretch very little and require some sort of tensioning device.
A typical V-belt would shred itself at start up if it didn't have layers of dacron, kevlar or some other high strength cords running the length of the belt.
FYI: V-belts are not made as individual belts but are made on a long drum. Layers of rubber are built up uniformly on the drum and covered with a long continuous cord wound from one end to the other. Another layer of rubber and possibly more cord layers. All topped off with more rubber. Than it's vulcanized and while still on the drum knives are used to cut the individual belts to the required width.
This can be seen on a new belt, the cord material will be seen to have been cut when looking at the side of the belt.

BillWojo

 

[Nat]

I don't think there was very much stretch at all to the belt for the Grey table. I suspect that our common intuition that a belt should be stretchy is probably largely incorrect. There needs to be enough tension to produce enough friction to transmit power, but a really springy belt would make the platter oscilate in its speed. This does happen to a degree, but it needs to be very limited.

 

[John Berard]

If the belt has threads or cords running the length of the belt it will stretch very little and require some sort of tensioning device.

I think the threads are more like a woven fabric impregnated with rubber. It would not be the typical 'ply' like construction. Some have described it as a fiber type rubber. I have not seen one myself but would like to get one just to examine. On my Stromberg PR-500 there is not a tension device. One of the motors can simply be moved in or out from the spindle center giving me the opinion that the belt is stretchy enough (or plyable) to create grip and conform the the pulley apex.

I don't think there was very much stretch at all to the belt for the Grey table. I suspect that our common intuition that a belt should be stretchy is probably largely incorrect. There needs to be enough tension to produce enough friction to transmit power, but a really springy belt would make the platter oscilate in its speed. This does happen to a degree, but it needs to be very limited.

I am of common thought on this. Obviously it is a fine balance. If using a 100% rubber (or some other compound), the thickness and durometer rating would need to be considered. Proper speed is dependent on the belt since the effective pulley radius is based on the centerline of the belt thickness.

 

[AdamAnt316]

My NOS Rek-O-Kut K33 kit came with what appears to be some sort of fabric belt. Not sure if it is/was coated in rubber, since it's still inside the plastic baggie. Guessing it wouldn't last too long if I tried to run the table with it after building said kit 60+ years after it was made, but who knows. It can be seen somewhere within the box of parts seen below:

And for good measure, a couple more photos of the K33:

 

[eiraved]

My NOS Rek-O-Kut K33 kit came with what appears to be some sort of fabric belt. Not sure if it is/was coated in rubber, since it's still inside the plastic baggie. Guessing it wouldn't last too long if I tried to run the table with it after building said kit 60+ years after it was made, but who knows.

That's a nice rare find, NOS and all! I'm betting the belt will do just fine, even after over a half century. Good thing it wasn't made within the last couple of decades or else there would've been an expiration date on the bag!

 

[John Berard]

My NOS Rek-O-Kut K33 kit came with what appears to be some sort of fabric belt.

Wow, you lucky dog! IF you ever get up the gumption to open that belt bag, make sure to take some close-up pictures and measure the width and thickness.