Sansui SR-2050C speed issue

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Sansui SR-2050C speed issue

Post by Tube Radio » 17 Nov 2017 22:43

I have a Sansui SR-2050C turntable I got for free from a forum member on another forum after a tree hit my trailer in early January and destroyed a perfectly good Pioneer PL-530 along with a real good condition album Backstabbers by the O'Jays that was left on the platter which I will never be doing again.

It has a slight speed issue where it runs slightly slow in both 33 and 45.

I cleaned and lubed what should be cleaned and lubed and it didn't seem to help much and everything seems to move as it should.

The belt seems ok, but I'm not sure.

Here's a photo of the belt. Is it ok or is it stretched?
20171117_173716-600x800.jpg
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Now given a part is missing at the end of the string on the tonearm would this be a turntable worthy of perhaps fitting another arm on in place of the original if it is even possible to do so?

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Re: Sansui SR-2050C speed issue

Post by musicmn » 18 Nov 2017 15:46

Hi tube radio, I currently own a Sr 2050c and have serviced quite a few of these turntables. The belt you have is in need of replacement. The belt should fit snugly on the rim of the platter not tight or so loose that it just falls off. The belt you need is a FBM 25.0" but do not go out and buy just any FBM 25.0" belt. There are differences in the width and thickness of these belts between sellers. I personally bought belts from different ebay sellers over the yrs and found that some are to thick and tall and some are to thin. If the belt is to thick and tall it will cause the platter to run slow and if the belt is to thin it will usually make the platter run to fast. This is especially true on AC motor driven turntabels that rely on the mains power to keep the platter speed consistent. The only time the belt thickness and width really do not matter is with a DC motor driven turntable with pitch controls that be adjusted to bring the platter to the correct speed. I have found only a couple of sellers who have belts that work consistently at getting the platter speed correct on both 33.3 and 45.0. I will PM them to you so you can buy from who ever you want. Now on this turntable the motor has some tubes with wicks in them to carry oil to the top and bottom bearings. On most of these motors the tubes are broken or cracked and the oil just drips into the bottom of the turntable never getting to the bearings. Make sure the tubes on your motor are in good shape and make sure the oil you are using gets to the bearings. You should actually be able to see the oil go down the wick to the bearings. If the tubes are cracked then you will need to disassemble the motor and remove the tubes. Then disassemble the bearings and flush the old oil from them. Then put fresh oil in each bearing before you assemble the motor. I like to use Zoom spout Turbin oil for electric motors, or you can use sewing machine oil, but some people feel it's to light weight for turntable motors. Again it's up to you what to use and do some research on. Make sure that the rim on the under side of the platter and the pulley on the motor are clean and free of any old belt gunk before you install a new belt. If you want the weight of the string weight I can get that for you if you want to try and make one for yourself. But I will tell you that the cartridge will track fine with out it. And the tonearm is very nice and worth keeping on the turntable.I hope this helps.

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Re: Sansui SR-2050C speed issue

Post by Tube Radio » 18 Nov 2017 16:50

Thanks.

One tube was broken so I replaced it with a small piece of rubber hose.

Seems to work ok.

Given it will track good without the weight I'll not bother with it.

I'll leave the tonearm alone then.

The capacitors inthe auto arm lifter do they need to be replaced or are they the type that don't usually go bad.

Also I gotta figure why the auto lifter works, but the part that lifts the tonearm doesn't seem to do that.

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Re: Sansui SR-2050C speed issue

Post by Tube Radio » 01 Dec 2017 01:43

Interestingly enough with the belt just on the platter the last few days it is now tight like it should be on the platter.

The only thing I don't recall doing was cleaning the belt.

Think I got some stuff to clean it with so I may try that first.

Looked at the platter again and where the belt goes there was still some tiny specs of either that belt or a previous belt which wouldn't come off easily.

I took some #000 steel wool and removed them then cleaned the platter.

Not sure if that helped.

Is there any strobe disc that can be printed directly to 8 1/2" X 11" paper and be right?

I tried a couple before and both were not correct when printed or maybe I just didn't print them right.

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Re: Sansui SR-2050C speed issue

Post by Spinner45 » 01 Dec 2017 02:45

Tube Radio wrote:Interestingly enough with the belt just on the platter the last few days it is now tight like it should be on the platter.

The only thing I don't recall doing was cleaning the belt.

Think I got some stuff to clean it with so I may try that first.

Looked at the platter again and where the belt goes there was still some tiny specs of either that belt or a previous belt which wouldn't come off easily.

I took some #000 steel wool and removed them then cleaned the platter.

Not sure if that helped.

Is there any strobe disc that can be printed directly to 8 1/2" X 11" paper and be right?

I tried a couple before and both were not correct when printed or maybe I just didn't print them right.
Signs of belt residue on pulleys and platter indicate a deteriorating belt.
Replace it.

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Re: Sansui SR-2050C speed issue

Post by Tube Radio » 01 Dec 2017 03:14

Will do.

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Re: Sansui SR-2050C speed issue

Post by Tube Radio » 26 Oct 2018 15:04

A long awaited update.

Got the belt replaced and still ran slow.

Found that the shaft the platter sits on had some resistance to it which I thought was normal, but figured maybe that was the problem. So I cleaned and re-lubed it. The shaft turns a bit more freely now, but that didn't help at all.

Motor in my opinion turns as free as an AC motor with a magnetic rotor should turn.

The only thing I have left is to disassemble the motor, clean and re-lube it and see if that helps.

If the speed is still too slow then I don't know what else it could be.

Also I found why the function that raises the arm at the end of the record doesn't work.

The rubber grommets are bad.

What would be a proper replacement?

Also I might change the motor grommets as well.

The new belt looked to be the same thickness and width as the old belt so I'm pretty sure it is the correct belt.

On 33 1/3 it is running around 32 1/2 RPMs and 45 RPMs is slow by about the same percentage as the 33 is.

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Re: Sansui SR-2050C speed issue

Post by Spinner45 » 26 Oct 2018 17:43

Tube Radio wrote:
26 Oct 2018 15:04
A long awaited update.

Got the belt replaced and still ran slow.

Found that the shaft the platter sits on had some resistance to it which I thought was normal, but figured maybe that was the problem. So I cleaned and re-lubed it. The shaft turns a bit more freely now, but that didn't help at all.

Motor in my opinion turns as free as an AC motor with a magnetic rotor should turn.

The only thing I have left is to disassemble the motor, clean and re-lube it and see if that helps.

If the speed is still too slow then I don't know what else it could be.

Also I found why the function that raises the arm at the end of the record doesn't work.

The rubber grommets are bad.

What would be a proper replacement?

Also I might change the motor grommets as well.

The new belt looked to be the same thickness and width as the old belt so I'm pretty sure it is the correct belt.

On 33 1/3 it is running around 32 1/2 RPMs and 45 RPMs is slow by about the same percentage as the 33 is.
33 1/2 would be running "fast", not slow.
Nevertheless, those speeds are within tolerances for mass produced units.
So I wouldn't get too "picky" over it.

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Re: Sansui SR-2050C speed issue

Post by Tube Radio » 26 Oct 2018 17:49

Meant to say 32 1/2 not 33 1/2

It is off enough so that I notice it.

Now if it was 33 1/2 more than likely I'd notice it as well.

I'll disassemble the motor today and take it to work tomorrow where I have the proper stuff to clean it with then clean and lube it.

I do know one newer phono could run straight from 120Vac or it could be plugged into an optional speed control which I think put out 120Vac and just varied the frequency.

If all else fails I can find something like that and increase the speed enough.

I really wanted a direct drive or another Pioneer PL-530, but when you get an offer of one for cost of shipping you take whatever is offered and from what I understand after asking on another forum the record player is actually quite good and has a good arm on it.

In all honesty if I can only get 33 1/3 correct that will be fine as I have a RCA 45 player I converted to stereo for my 45s.

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Re: Sansui SR-2050C speed issue

Post by Spinner45 » 26 Oct 2018 18:14

Tube Radio wrote:
26 Oct 2018 17:49
Meant to say 32 1/2 not 33 1/2

It is off enough so that I notice it.

Now if it was 33 1/2 more than likely I'd notice it as well.

I'll disassemble the motor today and take it to work tomorrow where I have the proper stuff to clean it with then clean and lube it.

I do know one newer phono could run straight from 120Vac or it could be plugged into an optional speed control which I think put out 120Vac and just varied the frequency.

If all else fails I can find something like that and increase the speed enough.

I really wanted a direct drive or another Pioneer PL-530, but when you get an offer of one for cost of shipping you take whatever is offered and from what I understand after asking on another forum the record player is actually quite good and has a good arm on it.

In all honesty if I can only get 33 1/3 correct that will be fine as I have a RCA 45 player I converted to stereo for my 45s.
Fixed-speed turntables are known for their "tolerances" regarding speed accuracy.
And a new belt may be tighter until "broken in" and cause tiny bit of slowness at first.
These are all normal things, nothing to fuss over, and the general population would be satisfied with that.

People that are "picky" over speed issues, or are "pitch sensitive", would then buy a turntable that has adjustable speeds to satisfy their need.

It's all about tier level, price point, and manufacturing.

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Re: Sansui SR-2050C speed issue

Post by Tube Radio » 27 Oct 2018 03:53

I'm very pitch sensitive.

That said I'd find it hard to believe that something like a sansui would be running slow especially when other cheaper record players are at the right speed.

That said if cleaning and lubing the motor doesn't work I'll look for something that can vary the frequency of the ac voltage and speed it up that way.

That said the motor has plenty of torque enough so that the motor still spins when the platter is stopped (only done once very briefly) so I find it hard to believe it would be bogged down by a new belt.

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Re: Sansui SR-2050C speed issue

Post by Coffee Phil » 27 Oct 2018 04:55

Hi Tube Radio,

It turns out that belt thickness has an effect on platter speed. Your machine has a 4 pole synchronous motor which turns at 1800 RPM on 60 Hz. That is pretty fast by today’s standards and it forces a very small capstan. The effective radius of the capstan includes ~ 1/2 the belt thickness so with small capstans this effect is pronounced.

Typically on machines with 4 pole motors such as my R-O-K Rondine 2 the trick is to get a belt thin enough. It appears that your belt is too thin.

If you want to do a speed box here is a cost effective approach:

gallery/image/26542/medium

This is a function generator driving an audio power amp, the output of which is stepped up with a transformer. Driving a motor is a lowly task for a nice tube amp like the old Fisher. Some Class D sand thing should do fine.

Phil
Tube Radio wrote:
27 Oct 2018 03:53
I'm very pitch sensitive.

That said I'd find it hard to believe that something like a sansui would be running slow especially when other cheaper record players are at the right speed.

That said if cleaning and lubing the motor doesn't work I'll look for something that can vary the frequency of the ac voltage and speed it up that way.

That said the motor has plenty of torque enough so that the motor still spins when the platter is stopped (only done once very briefly) so I find it hard to believe it would be bogged down by a new belt.

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Re: Sansui SR-2050C speed issue

Post by Tube Radio » 27 Oct 2018 05:49

That idea of a speed control on the cheap is nice.

Suppose a good plate amp would work for that.

Would need a decent audio generator though which I don't have at the moment.

Unless the belt that came on it was not the original then I'm sure I have the right belt.

Gotta clean the motor then I'll know for sure.

Only thing I haven't done.

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Re: Sansui SR-2050C speed issue

Post by Spinner45 » 27 Oct 2018 07:46

Tube Radio wrote:
27 Oct 2018 03:53
I'm very pitch sensitive.

That said I'd find it hard to believe that something like a sansui would be running slow especially when other cheaper record players are at the right speed.

That said if cleaning and lubing the motor doesn't work I'll look for something that can vary the frequency of the ac voltage and speed it up that way.

That said the motor has plenty of torque enough so that the motor still spins when the platter is stopped (only done once very briefly) so I find it hard to believe it would be bogged down by a new belt.
You haven't been through enough turntables to understand the tolerences that are part of manufacturing.
Particularly with mass-produced products.
Yes, they (the manufacturers) aim for correct speed, but various samples CAN and WILL be slightly off.
The Quality Control department does tests, but it's quite possible that motor pulley manufacture has the occasional issues, resulting in differences.
Wear also happens, naturally.
And I've seen motors drop speed due to gummed bearings.

The lowly and inexpensive VM record changers come to mind, some are spot on, others are slow - tolerences, again.
If it's within say, 1 percent, they allow it to pass.
Same goes for the BSR's, among others.

And this is normal.

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Re: Sansui SR-2050C speed issue

Post by Tube Radio » 27 Oct 2018 13:03

Yes I've seen more BSRs run slightly fast than anything.

With those I just time how many RPMs the platter goes in 1 minute for the selected speed then with sand paper shave a little off the capstan for that speed and re-check then repeat until the speed is dead on.

I disassembled the motor and found two things.

There was some old oil in the bottom bushing which could have slowed the motor down some.

Also the fan on the bottom had come unglued from the rotor which might have been a contributing factor.

Cleaned everything and lubed the bushings.

Waiting on the epoxy to cure which according to the instructions it will be set ijn 4-8 hours at 77F.

Where I work is not 77F inside the building so I set the rotor lightly clamped in a vice (to keep pressure on the fan) in front of the fan output of a Tektronix 2246 scope which will put out at least 77F or higher temperature air once the scope warms up.

I will reinstall the motor this afternoon and check the speed.

If it is now the right speed then I am done.

If it is still not the right speed then I'll look into building that speed control which shouldn't be too hard as I may have an amp that will work and can figure a way to generate the proper sinewave plus I have some transformers at my disposal.

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