Garrard 401 idler bearing - Page 2 - UK Vintage Radio Repair and Restoration Discussion Forum

stevehertz · 14th Apr 2021, 2:12 pm

Quote:

Originally Posted by Beobloke

Quote:

Originally Posted by stevehertz

Thanks Bill. I may well purchase that but I'm just wondering if manufacturer's service data from half a century ago will cover what a 401 may need today in terms of long term faults and problems, tips etc. I'm sure lots of it, dismantling etc will be very relevant. Mine holds a speed 'perfectly' apart from a cyclical blip that for all the world looks like an idler flat - I've changed it - or a stiff spot somewhere, somehow.

Out of interest, have you confirmed this behaviour with a separate strobe disc?

The reason I ask is that I remember driving myself half mad with a similar issue years ago on a much cheaper turntable. Turned out it must have been a machining issue on the strobe markings as it was fine with a separate strobe disc or a test LP/W&F meter!

I haven't tried a different strobe disc, but it is the original screen printed strobe disc by Garrard. So I doubt if it's the problem?

dave cox · 14th Apr 2021, 2:57 pm

The rotation speed (at some speeds?) is not an integral of 20mS/50Hz to there is a bit of a jump each revolution! This is probably what you are seeing /

dc

Bufo Bill · 14th Apr 2021, 3:59 pm

Hmm, I may not have been as fastidious with my restoration as I had hoped. I am having a slippage of the platter and the general speed is very fast, when I switch on from cold the speed adjustment needs to be right on minimum. Any suggestions welcome.

Bufo Bill · 14th Apr 2021, 5:26 pm

Okay, I calmed myself down and went through the manual again. I went through the section on adjusting the speed, and found that bolt in the motor casing, the one with the screw that adjusts the magnet assembly. I wound it down as the book instructs, but found that the magnet rubbed on the fly wheel (is that the term)? It was still too fast, so I took a leap and lowered the collar on the fly wheel. I am still getting it fine tuned, but I believe I can get this right. We shall find out if that sorts out the "wobble" in the speed.

stevehertz · 14th Apr 2021, 6:01 pm

Quote:

Originally Posted by dave cox

The rotation speed (at some speeds?) is not an integral of 20mS/50Hz to there is a bit of a jump each revolution! This is probably what you are seeing /

dc

That's very interesting Dave, thanks. What's the explanation behind it?

Beobloke · 14th Apr 2021, 6:32 pm

Quote:

Originally Posted by stevehertz

I haven't tried a different strobe disc, but it is the original screen printed strobe disc by Garrard. So I doubt if it's the problem?

Is it also visible on the platter strobe markings?

analogadikt · 15th Apr 2021, 5:19 am

Quote:

Originally Posted by Bufo Bill

but found that the magnet rubbed on the fly wheel (is that the term)?

It is the Eddy (current) brake disc.

Regards,

Anwesh

Craig Sawyers · 15th Apr 2021, 7:15 am

The 401 was a real workhorse. The BBC used them for all music broadcasts when records were the only show in town. And before that they used the 301. They turned them on in the morning, left them running all day, and turned them off after the last broadcast.

They are extremely rugged, and the strobe markings are machine cut around the periphery of the turntable, so not a chance that there is any error in the strobe.

The motor is a massive unit in a serious cast metal shell to shield hum field. It is so chunky to compensate for any cartridge that needed a high tracking force.

To set the speed accurately there is an eddy current brake on the motor shaft. That is an aluminium disc with magnets below and above the disc on a pivoted arm whose position is controlled by the middle knob at the front. You adjust it so that the strobe markings remain stationary.

The mechanism is similar in the 301, other than only one magnet being used.

Because the magnets are balanced above and below the disc in the 401, the braking effect is certainly to at least first order independent of the position of the magnets relative to the disc, and to disc wobble.

Craig

Bufo Bill · 15th Apr 2021, 10:48 am

Namaste Anwesh, thank you for clearing that up for me.
Craig, your in-depth and concise posts have helped a lot with my knowledge of the workings of the 401. Thanks.
I looked at everything again last night, and found a little gap between the thrust plate and the bearing housing at one end. That seems to solve the problem once the deck has been going a few minutes.
The sound is fabulous and the P8ES now tracks everything I have thrown at it at .75gm.
Thanks guys, from Bill.

barrymagrec · 15th Apr 2021, 11:11 am

My memory of using a brand new 401 in the seventies was that it always started slightly fast then settled down after 20 minutes or so. You could adjust this with the speed control but it wasn`t noticeable in practice.

This effect (and a sensitivity to mains voltage) was mentioned in the original HiFi News review which suggested it was due to motor changes from the 301 in order to reduce the notorious hum problem that Decca FFSS users found.

I still have the 401 but it has not been used for nearly forty years, I intend to bring it back to life soon.

Bufo Bill · 15th Apr 2021, 12:44 pm

Barry, when you do get round to the restoration, take a look at the Classic Turntable Co.
www.classichifi-shop.co.uk
I used the service kit that they offer, and their bearing kit and Thrust Plate bearing upgrade with integral seal. My turntable is much better for all of it. They offer a restoration service (haven't used it myself so can't comment on it).
Peak Hifi have also been very helpful to me.
www.peakhifi.co.uk
Cheers from Bill.

Ted Kendall · 15th Apr 2021, 3:15 pm

Quote:

Originally Posted by Bufo Bill

The sound is fabulous and the P8ES now tracks everything I have thrown at it at .75gm.

That's pushing it, really - you would do much better to run at 1 or 1.25g. Record wear is negilgible at these pressures, and far more damage is caused to the disc by mistracking, however marginal it be.

Bufo Bill · 15th Apr 2021, 3:35 pm

Thanks for the advice Ted. Better safe than sorry, eh?
Cheers from Bill.

dave cox · 16th Apr 2021, 3:21 pm

50Hz Strobe at 33 1/3,45 & 78 RPM

At 33 1/3 RPM, each revolution takes 1.8 seconds and 90 x 20mS (@50Hz) divisions fit exactly at the exact speed.

At 45 RPM, each revolution takes 1 1/3 seconds so you can either have 66 (1% slow) or 67 (0.5% fast) divisions. Even 0.5% is a bit rubbish so the better option is to have a single 2/3 division. This makes a bit of a jump when you view it!

For 78 RPM the error is gross!

dc

Bufo Bill · 16th Apr 2021, 4:27 pm

I love it when people write out the maths, it really helps me. Cheers Dave!
Bill.

Trigon. · 16th Apr 2021, 5:27 pm

A 401 turntable is marked with 77, 133, and 180 timing divisions. (For 50Hz mains.)

A neon strobes at 100Hz, i.e. 0.01 sec. When the marks are stationary the turntable has rotated 1 division in 0.01 sec, so:-

77 x 0.01 sec = 0.77 sec per rev , 1/0.77= 1.299 Hz = 77.92 rpm (0.1% slow)
133 x 0.01 sec = 1.33 sec per rev , 1/1.33 = 0.752 Hz = 45.11 rpm (0.25% fast)
180 x 0.01 sec = 1.80 sec per rev , 1.1.8 = 0.556 Hz = 33.33 rpm (exact)

Cheers

Bufo Bill · 16th Apr 2021, 6:23 pm

I like that! Thanks so much for taking the time to write that out and post. That fills it out a bit more in my mind.
Cheers from Bill.

Bufo Bill · 24th Apr 2021, 4:31 pm

Final report time! The thrust plate had been unevenly tightened and a gap of <1mm had appeared as stated above. I tightened the screw and the turntable runs steady now. My new Plinth from Peak Hifi should be done soon, hurrah!
Bill.

14th Apr 2021, 2:57 pm	#22
dave cox Nonode Join Date: Jan 2009 Location: Bristol, UK. Posts: 2,061	Re: Garrard 401 idler bearing The rotation speed (at some speeds?) is not an integral of 20mS/50Hz to there is a bit of a jump each revolution! This is probably what you are seeing / dc

14th Apr 2021, 3:59 pm	#23
Bufo Bill Heptode Join Date: Jan 2016 Location: Wolverhampton, West Midlands, UK. Posts: 777	Re: Garrard 401 idler bearing Hmm, I may not have been as fastidious with my restoration as I had hoped. I am having a slippage of the platter and the general speed is very fast, when I switch on from cold the speed adjustment needs to be right on minimum. Any suggestions welcome.

14th Apr 2021, 5:26 pm	#24
Bufo Bill Heptode Join Date: Jan 2016 Location: Wolverhampton, West Midlands, UK. Posts: 777	Re: Garrard 401 idler bearing Okay, I calmed myself down and went through the manual again. I went through the section on adjusting the speed, and found that bolt in the motor casing, the one with the screw that adjusts the magnet assembly. I wound it down as the book instructs, but found that the magnet rubbed on the fly wheel (is that the term)? It was still too fast, so I took a leap and lowered the collar on the fly wheel. I am still getting it fine tuned, but I believe I can get this right. We shall find out if that sorts out the "wobble" in the speed.

15th Apr 2021, 7:15 am	#28
Craig Sawyers Dekatron Join Date: Nov 2010 Location: Oxford, UK. Posts: 4,978	Re: Garrard 401 idler bearing The 401 was a real workhorse. The BBC used them for all music broadcasts when records were the only show in town. And before that they used the 301. They turned them on in the morning, left them running all day, and turned them off after the last broadcast. They are extremely rugged, and the strobe markings are machine cut around the periphery of the turntable, so not a chance that there is any error in the strobe. The motor is a massive unit in a serious cast metal shell to shield hum field. It is so chunky to compensate for any cartridge that needed a high tracking force. To set the speed accurately there is an eddy current brake on the motor shaft. That is an aluminium disc with magnets below and above the disc on a pivoted arm whose position is controlled by the middle knob at the front. You adjust it so that the strobe markings remain stationary. The mechanism is similar in the 301, other than only one magnet being used. Because the magnets are balanced above and below the disc in the 401, the braking effect is certainly to at least first order independent of the position of the magnets relative to the disc, and to disc wobble. Craig Last edited by Craig Sawyers; 15th Apr 2021 at 7:22 am.

15th Apr 2021, 10:48 am	#29
Bufo Bill Heptode Join Date: Jan 2016 Location: Wolverhampton, West Midlands, UK. Posts: 777	Re: Garrard 401 idler bearing Namaste Anwesh, thank you for clearing that up for me. Craig, your in-depth and concise posts have helped a lot with my knowledge of the workings of the 401. Thanks. I looked at everything again last night, and found a little gap between the thrust plate and the bearing housing at one end. That seems to solve the problem once the deck has been going a few minutes. The sound is fabulous and the P8ES now tracks everything I have thrown at it at .75gm. Thanks guys, from Bill.

15th Apr 2021, 11:11 am	#30
barrymagrec Octode Join Date: Dec 2017 Location: Morden, Surrey, UK. Posts: 1,557	Re: Garrard 401 idler bearing My memory of using a brand new 401 in the seventies was that it always started slightly fast then settled down after 20 minutes or so. You could adjust this with the speed control but it wasn`t noticeable in practice. This effect (and a sensitivity to mains voltage) was mentioned in the original HiFi News review which suggested it was due to motor changes from the 301 in order to reduce the notorious hum problem that Decca FFSS users found. I still have the 401 but it has not been used for nearly forty years, I intend to bring it back to life soon.

15th Apr 2021, 12:44 pm	#31
Bufo Bill Heptode Join Date: Jan 2016 Location: Wolverhampton, West Midlands, UK. Posts: 777	Re: Garrard 401 idler bearing Barry, when you do get round to the restoration, take a look at the Classic Turntable Co. www.classichifi-shop.co.uk I used the service kit that they offer, and their bearing kit and Thrust Plate bearing upgrade with integral seal. My turntable is much better for all of it. They offer a restoration service (haven't used it myself so can't comment on it). Peak Hifi have also been very helpful to me. www.peakhifi.co.uk Cheers from Bill.

15th Apr 2021, 3:35 pm	#33
Bufo Bill Heptode Join Date: Jan 2016 Location: Wolverhampton, West Midlands, UK. Posts: 777	Re: Garrard 401 idler bearing Thanks for the advice Ted. Better safe than sorry, eh? Cheers from Bill.

16th Apr 2021, 3:21 pm	#34
dave cox Nonode Join Date: Jan 2009 Location: Bristol, UK. Posts: 2,061	Re: Garrard 401 idler bearing 50Hz Strobe at 33 1/3,45 & 78 RPM At 33 1/3 RPM, each revolution takes 1.8 seconds and 90 x 20mS (@50Hz) divisions fit exactly at the exact speed. At 45 RPM, each revolution takes 1 1/3 seconds so you can either have 66 (1% slow) or 67 (0.5% fast) divisions. Even 0.5% is a bit rubbish so the better option is to have a single 2/3 division. This makes a bit of a jump when you view it! For 78 RPM the error is gross! dc

16th Apr 2021, 4:27 pm	#35
Bufo Bill Heptode Join Date: Jan 2016 Location: Wolverhampton, West Midlands, UK. Posts: 777	Re: Garrard 401 idler bearing I love it when people write out the maths, it really helps me. Cheers Dave! Bill.

16th Apr 2021, 5:27 pm	#36
Trigon. Hexode Join Date: Jun 2018 Location: Buckinghamshire, UK. Posts: 387	Re: Garrard 401 idler bearing A 401 turntable is marked with 77, 133, and 180 timing divisions. (For 50Hz mains.) A neon strobes at 100Hz, i.e. 0.01 sec. When the marks are stationary the turntable has rotated 1 division in 0.01 sec, so:- 77 x 0.01 sec = 0.77 sec per rev , 1/0.77= 1.299 Hz = 77.92 rpm (0.1% slow) 133 x 0.01 sec = 1.33 sec per rev , 1/1.33 = 0.752 Hz = 45.11 rpm (0.25% fast) 180 x 0.01 sec = 1.80 sec per rev , 1.1.8 = 0.556 Hz = 33.33 rpm (exact) Cheers Last edited by Trigon.; 16th Apr 2021 at 5:33 pm.

16th Apr 2021, 6:23 pm	#37
Bufo Bill Heptode Join Date: Jan 2016 Location: Wolverhampton, West Midlands, UK. Posts: 777	Re: Garrard 401 idler bearing I like that! Thanks so much for taking the time to write that out and post. That fills it out a bit more in my mind. Cheers from Bill.

24th Apr 2021, 4:31 pm	#38
Bufo Bill Heptode Join Date: Jan 2016 Location: Wolverhampton, West Midlands, UK. Posts: 777	Re: Garrard 401 idler bearing Final report time! The thrust plate had been unevenly tightened and a gap of <1mm had appeared as stated above. I tightened the screw and the turntable runs steady now. My new Plinth from Peak Hifi should be done soon, hurrah! Bill.