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Signal chain in 'the old days' of tape

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Re: Signal chain in 'the old days' of tape

Postby ceejay » Sun Jun 02, 2019 11:35 am

... digressing a little (well, a lot really) someone pointed out in another forum that videotape had been invented, developed, become the mainstay of the television industry and then completely disappeared ... all in his lifetime - mine too!!!
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Re: Signal chain in 'the old days' of tape

Postby Tim Gillett » Sun Jun 02, 2019 11:36 am

ef37a wrote:Ah now TIm! This was explained to me MANY years ago at a two day service tech's training course* at Sony UK (those WERE the days!) .

The capstan flywheels are driven by a belt around a single motor pulley. The feed side of the belt is in compression and the leave side in tension. If you get the 3 shaft centres right and the belt's characteristics correct the system gives just the right speed differential to get the right tape tension across the heads.

I certainly have never had any tape damage problems with my machine and have never had any back in the day. What would "servicing" consist of? Keeping things clean is a no brainer with any tape machine. Change the oil after 2,000 cassettes?

*Travel cost probably tax deductible for the SE?

Dave.
Hi Dave,

I always assumed there was a slight difference in outer diameter on the two flywheels, leading to slightly faster rotation of the supply flywheel with both driven by the same belt. Some dual capstan designs link the two flywheels by a common belt and a separate belt directly drives the take up flywheel. Obviously in that arrangement the tendency would be for the indirectly driven flywheel to rotate a little slower due to any creep of the inter-flywheel belt.

So you're saying even in the one belt situation the flywheel driven directly from the motor runs slightly faster than the one driven from that flywheel, and that's enough of a speed differential to achieve reliable tape tension? I'm not disagreeing. I've just never came across it or considered it.

Tim
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Re: Signal chain in 'the old days' of tape

Postby ef37a » Sun Jun 02, 2019 12:46 pm

Yes Tim, I think it was just serendipity!

Sony may have calculated what the theoretical difference in the two flywheels would have needed to be to give the speed differential but then in practice found it was to high!

Back of a fag packet calc' later and Bazinga! The sums come out right for identical diameters.

Went to quite a few manfctr's training sessions. I never understood why they gave us wine at lunch? We learned FA after!

The two nighter for Rumbelows was bloody good grub but there was NOTHING to do in Nantwich after 9pm!

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Re: Signal chain in 'the old days' of tape

Postby Tim Gillett » Sun Jun 02, 2019 2:31 pm

Dave, living on t'other side of the world and not so keen on travel as I used to be, I'll probably never have the pleasure of meeting you in person but great to occasionally converse on this SOS forum, learn from your great experience and be entertained with your own special style. Here's to ya. :clap:

Tim
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Re: Signal chain in 'the old days' of tape

Postby Mike Stranks » Sun Jun 02, 2019 4:40 pm

Tim Gillett wrote:
Mike Stranks wrote:I had a cassette deck in the mid 70s - Toshiba... Twin-capstan which had a tendency to mangle tape at the drop of a hat.

... Possibly your machine just needed a good service.


It was at the repairers two or three times during my ownership in an attempt to fix the problem. As I'd bought it secondhand there was no question of warranty-fixes. In the end it resided in my father-in-law's workshop for many years awaiting his attentions, but eventually was just scrapped. :(
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Re: Signal chain in 'the old days' of tape

Postby ef37a » Sun Jun 02, 2019 7:01 pm

Tim Gillett wrote:Dave, living on t'other side of the world and not so keen on travel as I used to be, I'll probably never have the pleasure of meeting you in person but great to occasionally converse on this SOS forum, learn from your great experience and be entertained with your own special style. Here's to ya. :clap:

Tim
Aw, shucks!
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Re: Signal chain in 'the old days' of tape

Postby Tim Gillett » Tue Jun 04, 2019 6:19 am

ef37a wrote:I certainly have never had any tape damage problems with my machine and have never had any back in the day. What would "servicing" consist of? Keeping things clean is a no brainer with any tape machine. Change the oil after 2,000 cassettes?
Dave.

Change the oil isnt that far off but if only tape machines had a sump, oil filter and the ability to just replace oil and filter so that every bearing surface inside the tape machine was now given a fresh supply of constantly filtered oil - under pressure.

Instead there are various little bearings with oil or grease loaded at time of manufacture. Many of them they were called "lubrication free" in the service manual which meant "for the service life of the machine". Forty or fifty years on it's a different story.

Currently I have an Otari 4 track 1/2" machine open on the bench. Its pinch roller arm bush is seized due to old, dried up grease. Until that is cleaned out and new lubricant replaces it - a common problem with many makes and models of tape machine - the machine is pretty much useless. You could say I'm an electronics technician but much of the time "mechanic" would be more apt. Cleaner and mechanic.

I still make a little money servicing tape machines but when I want to record audio, it's digital recorders using flash memory. They tell me there are no greasing points in them...
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Re: Signal chain in 'the old days' of tape

Postby ef37a » Tue Jun 04, 2019 8:24 am

Yes Tim I forgot about the really big, really old stuff.

I used to get the odd seized record player motor back in the days of open fires and everyone smoking.
I used to get them apart and leave the sintered bronze bearings soaking in 3-in-1 oil overnight, quick wipe in the morning, good for another ten years!
New stylus, the kids NEVER changed those. The ultimate cheap as chips record player consisted of a single UL84, heater fed from a 90V tap on the motor winding and HT via a diode straight off the mains! The high output cartridge could deliver up to ten volts! GAKnows what the distortion level was but they were quite loud.

Oh yes! degrease the jockey wheel and turntable inner rim.

Dave.
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Re: Signal chain in 'the old days' of tape

Postby ken long » Tue Jun 04, 2019 8:41 pm

Hugh Robjohns wrote:tape wasn't intended to change the recorded sound, and all the relevant manufacturers put in massive engineering effort to make it as linear and as clean as they possibly could.

This.

Nothing wrong with hitting it hard but it can sometimes over egg the pudding.

And that reads wrong on a few levels :o
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Re: Signal chain in 'the old days' of tape

Postby Folderol » Tue Jun 04, 2019 9:54 pm

ef37a wrote:Yes Tim I forgot about the really big, really old stuff.

I used to get the odd seized record player motor back in the days of open fires and everyone smoking.
I used to get them apart and leave the sintered bronze bearings soaking in 3-in-1 oil overnight, quick wipe in the morning, good for another ten years!
New stylus, the kids NEVER changed those. The ultimate cheap as chips record player consisted of a single UL84, heater fed from a 90V tap on the motor winding and HT via a diode straight off the mains! The high output cartridge could deliver up to ten volts! GAKnows what the distortion level was but they were quite loud.

Oh yes! degrease the jockey wheel and turntable inner rim.

Dave.
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