SL65B anti-skating/bias

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amagasakii
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SL65B anti-skating/bias

Post by amagasakii » 04 Jan 2020 12:05

Super quick question while it's on my mind:

Should I expect the anti-skating spring on my SL65B to function similarly to that on my Duals or on my Japanese decks? If I float the arm at 0 VTF and move it to the spindle, then set the anti-skate to, say, the maximum of "6", should it pull the tonearm back to the rest, or move it at all? Or is there simply so much friction in the Autoslim mechanism that this isn't possible?

Much obliged!

lenjack
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Re: SL65B anti-skating/bias

Post by lenjack » 04 Jan 2020 15:46

With the arm floating, any amount of antiskate should cause the arm to swing out towards the rest.

DSJR
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Re: SL65B anti-skating/bias

Post by DSJR » 04 Jan 2020 22:48

Agreed, but we're talking fifty year old basic autochangers here - albeit the top Autoslim model from the time...

Garrard underdid the anti-skate on these models right from new and also *greased* up the arm's horizontal pivots - you know where I'm going with this don't you? The theory on a basic autochange chassis like this one was that 'some' anti-skate was better than none at all and the previous pivoted weight affair on the previous generation of the 60/65/SP25 family was as good as useless in practise to be honest.

Below is a bodge but may work -

With the arm balanced out, the horizontal 'friction' won't be that low and even when new, it's more 'drag' caused by the grease in the bearing, coupled with slight friction in the 'friction link' which was modified a bit in this generation to reduce it's effect when playing, as it's never fully released.

Rather than take the whole bloomin' arm and underside mechanism to bits initially, try pushing firmly on the tonearm bearing cradle a few times. It's quite tough and these horizontal bearings are spring loaded (a vaguely 'flattened C' shaped bracket with top and bottom vertical 'studs,' the top one being screwed in, acting on balls in the main casting, one of them (the top one from memory) being spring loaded. This may free off the horizontal movement a little more. A very little oil on the friction link may help a little more.

Having done the above, balance out the arm so it floats. Set the bias (oh alright anti-skate) to '5' and take the arm to the centre. The arm should now lazily? move back to the rest - TOTALLY OPPOSITE to the over-biasing of the Dual 1214 we're discussing in the Dual room here... The typical Garrard 'Autoslim' lateral arm friction is around double that of the Dual 1214 spec (and several times higher than Dual's finest) although the very last belt driven models were better I remember. The competing BSR MP60/P128 family of decks had triple the Dual tonearm friction, so nearly double that of the Garrard and with in this case, over-specified anti-skate which certainly looked like it was working but in fact far too much for any given setting on the dial.

Hope this rambling helps a bit...

Setting anti-skate is always a compromise irrespective of the cartridge and tonearm used, so any dial indication is often a fair compromise as different diamond profiles have different needs at different stylus downforces. I won't bore you any more, but if you use a 2g tracking cartridge on the SL65B, set the anti-skate dial to 4 or 5 and you won't go far wrong.

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Re: SL65B anti-skating/bias

Post by amagasakii » 05 Jan 2020 04:49

I gave your suggestion a shot, DSJR. Strange things are happening:

Bias at 5, the tonearm will drift back to the rest as long as it's within an inch or two of it. Otherwise, nothing. Bias at 0, as I move the arm towards the centre, there's a build-up of spring tension about two inches into the platter. If I push the tonearm further, the tension is gone and doesn't return until I move the arm back to the post. Bias at 3, there's no spring tension whatsoever.

When I bought this it looked like someone had been fiddling with the tonearm. I'll have to look into this further.

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Re: SL65B anti-skating/bias

Post by DSJR » 05 Jan 2020 11:16

The bias spring is an open affair with two 'arms' (please excuse the description), one of which is pivoted and located on the deck plate or the casting/plastic cover there and the other attached and pivoted on the main lateral tonearm bearing assembly (the flattened 'C' shaped stamping #46 in the SP25 IV parts list in the library here). As the arm moves back and forth, this spring articulates and pivots back and forth at each end (best seen rather than described) but should be free to do this.

Just looked again and the SP25 III service manual shows the mostly identical mechanism parts rather more clearly as well as an excellent shot of the tonearm overload spring, which I'll try to remember for future reference. Sadly, both service sheets only discuss the bias correction as a complete assembly - damn!

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Re: SL65B anti-skating/bias

Post by amagasakii » 06 Jan 2020 05:28

DSJR wrote:
05 Jan 2020 11:16
as well as an excellent shot of the tonearm overload spring, which I'll try to remember for future reference.
I stumbled across the same diagram last night and had the same thought. :D

I found a thread over on UK Vintage Radio that talks about the bias mechanism; there's a tiny plastic spring retainer (155 in the diagram) that goes on the pickup lever.

My thought was my deck is either missing this piece, or the spring isn't hooked into it. In looking at the SP25 Mk IV parts diagram, however, I see piece is still there as #133, but now referred to as "Overload Spring Retainer", so, thankfully, this probably isn't the case!

Perhaps I'll just pull the bias compensation mechanism and see what's going on underneath... that's kind of my style! ;)

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Re: SL65B anti-skating/bias

Post by amagasakii » 06 Jan 2020 08:20

It pays to just look at the bloody thing.

Turns out #155/#133 is right there at the top of the pickup lever and it is not the Overload Spring Retainer; one end of the bias spring indeed fits into it. I can't get a good shot of it, but there it is. The spring looks like it might need to be straightened out a bit where it plugs into #155/#133.
bias-spring-155.jpg
There it is!
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Additionally, the tonearm wiring is getting hung up and snagged on the hole in the bias compensator assembly by the spring itself; I probably need to reroute the wiring at some point.
bias-spring-2.png
Hung up in the hole circled in red
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When I tore this thing down way back when, I didn't go so far as removing the pickup lever and upper and lower casting. I should probably do that and clean out the pivot bearings, as I'm sure they have old grease in them. Interesting that Garrard seem to have eliminated the upper spring-loaded ball bearing that was present on my 2025TC. It must be in there somewhere; I can't imagine how the cradle is sprung otherwise.

(There's no ball bearing or spring anywhere above the upper "post" anywhere in the exploded drawing.)
pickup-bearing.png
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On a positive note, I fixed the channel imbalance on this deck (louder L than R) by shimming one side of the cartridge to compensate for the "twist" in the headshell and ensure correct azimuth. Little victories. :)

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Re: SL65B anti-skating/bias

Post by A70BBen » 10 Jan 2020 18:47

On these units and all Autoslim chassis, the ball on which the tonearm pivot screw rotates, and the spring to provide end thrust are inside the tonearm base casting, not considered to be separate parts.

Antiskating is virtually superfluous on an SL65B if you are tracking at around 2 1/2 to 3 grams or under because there is so much lateral drag from the friction link. You really don't want antiskating adding too much outward thrust.

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Re: SL65B anti-skating/bias

Post by DSJR » 10 Jan 2020 23:50

Oh, it's not quite that bad - and the friction link was modified on these remember so not quite as intrusive ;) As I quoted from a long ago review of the related SP25 III (Hi Fi Sound comparison of the 25 III and BSR MP60 I remember), *some* bias correction is better than none :)

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Re: SL65B anti-skating/bias

Post by amagasakii » 11 Jan 2020 00:52

I'll have to take a look when I work on it. On my 2025TC the bottom ball bearing is pressed into the lower casting, while the spring and upper ball bearing are loose in the upper casting (you can guess how I discovered it's loose!) When I was reassembling it, I was surprised at how little friction was in the tonearm, right up until I started connecting the springs and links for the automatics; it'll be interesting to see how the SL65B is once the friction link is disconnected.
2025TC.png
2025TC upper casting from isometric parts diagram
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Re: SL65B anti-skating/bias

Post by DSJR » 11 Jan 2020 15:16

The 2025TC used the original friction link, where the two 'prongs' clipped at the end are pretty parallel. The 65B/25III and I think all subsequent models, opened one of the 'prongs' into more of a curve, which reduces the loading on the lower tonearm linkages. I think the 125SB used much the same under-deck parts and the horizontal bearing friction on this model at least, was pretty darned good at around 40mg (I seem to recall standard previous models were around 80mg and the BSR MP60/BDS80 competitors around 150mg).

I appreciate the above ain't gonna help the anti-skate stuff, but the usual recommendation for the 125SB was to set the anti skate dial to double the tracking force of the cartridge.

P.S. The 65B/SP25 III had the extra O (cushion) ring on the bottom of the rotating inner hub to quieten the mech down when cycling and it appears the 2025TC range and 3500 did as well as subsequent models. I can't repeat enough how much quieter these decks cycle with an intact O ring fitted.

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Re: SL65B anti-skating/bias

Post by amagasakii » 09 Feb 2020 23:58

I had a chance to get to the SL65B this weekend and give it a full teardown and cleaning. Turns out I've now had enough practice at this that I can do a complete teardown and reassembly without the parts diagram or consulting pictures. :shock:

The mechanism under the main casting was over-greased but it hadn't turned to cement, so I cleaned that up. When I removed the upper casting the cueing lever and lifting platform were coated in silicone oil— it either migrated on its own or a previous servicer was trying to damp the cueing in any way possible.

This grease on the tonearm pivot certainly wasn't helping.
SL65B-pivot-goo.jpg
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A70BBen, I see what you mean about the ball and spring in the upper casting. Same concept as the 2025TC but there's a "cap" on top to keep them in place.

I put the pivot back together dry, with the exception of a small amount of oil to keep the lower ball in place and kept grease/oil to a minimum on all other parts. After re-routing the tonearm wiring and re-installing the bias compensation spring I can say the cancelling force is…slightly better, but still easily overpowered by the friction of the aptly-named friction link. Bumping it up to 5 will now pull the tonearm back to the rest post, though only from about an inch past the platter.

Not that this was an unnecessary exercise. Whereas before, engaging the cueing lever would drag the tonearm across a few grooves with a scratch while lifting, it now lifts cleanly, straight up. Also, removing and reinstalling the bias spring fixed the weirdness of it binding slightly at 0.
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SL65B-bottom.jpg
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