Tonearm bearings

Discussion in 'Hi-Fi and General Audio' started by la toilette, Aug 12, 2010.

  1. la toilette

    la toilette Downright stupid

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    I've been looking to buy a used Linn tonearm for a Lenco deck, and I have read various cautionary comments about worn or tired bearings, which need to be avoided.

    I can see why tonearm bearings need to be of high quality to ensure smooth operation and not have unwanted play etc, but I don't really see why they should deteriorate much given that on the average deck they must surely have a pretty easy life?

    Is it all more complicated than I imagine?
     
    la toilette, Aug 12, 2010
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  2. la toilette

    Batty Registered Insane

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    lubricant dries out over time
     
    Batty, Aug 12, 2010
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  3. la toilette

    TonyL Club Krautrock Plinque

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    Many Linn tonearms date from a rather crazy period of the 80s where idiots (both dealers and punters) over-tightened all fittings to utterly absurd levels. I've personally seen several Ittoks where the arm height allen-bolt has been driven so hard into the pillar it has deformed it. Often arms abused in this way suffer from sticky lateral bearings as the force applied to the am pillar has actually deformed the ball races. This can be detected by free-floating the arm and allowing it to swing over the playing area, damaged bearings tend to move in a 'notchy' way, e.g. tend to want to stick at several specific points in their travel. Abused arms can similarly display loose bearings as damage can easily happen when over-tightening a cart to the shell whilst the arm is mounted on the turntable. Thankfully this ideology has now been largely discredited, but a lot of decent arms have been damaged. If an arm has dirty great gouges in in the headshell slots and noticeable dings on the arm pillar I'd consider it had been abused and avoid it. If it looks mint in these areas it's probably been well cared for. Unipivots are far easier to assess as they are so simple in construction, i.e. you can actually have a look at the pivot point and bearing surface.

    Tony.
     
    TonyL, Aug 12, 2010
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  4. la toilette

    la toilette Downright stupid

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    Ok, so first thing to do is to avoid arms with excessive marking around the headshell slots - definitely worth knowing, thanks Tony. I have seen those kind of marks on arms on ebay, but hadn't realised that they might indicate damage to bearings.

    I'm almost definitely going to end up buying something without having inspected it in the flesh, so the swing test is out really, but hopefully if I'm in the position to ask the right questions to the vendor then that should help me avoid the worst examples!

    I quite like the idea of trying a unipivot but not for this particular deck as other than the arm I'm keeping it fairly standard, but as Lenco's are currently cheap as chips I've picked up 3 and at least one of those will end up in a custom plinth with more opportunity to play with other arms.
     
    la toilette, Aug 12, 2010
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  5. la toilette

    TonyL Club Krautrock Plinque

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    I'd stick a wanted ad up here, on WigWam, pfm etc, you may well be able to find an arm from a known member or dealer who could vouch for it. I'm never comfortable buying second hand 'flat earth' arms sight unseen off eBay etc, there are just too many trashed ones out there. Other arms tend to be safer buys e.g. SME, Hadcock, many Japanese arms etc as they were so deeply unfashionable at the time they largely escaped the allen key wielding mentalists.

    Tony.
     
    TonyL, Aug 12, 2010
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  6. la toilette

    Richard Dunn

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    Richard Dunn, Aug 12, 2010
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  7. la toilette

    TonyL Club Krautrock Plinque

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    TonyL, Aug 12, 2010
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  8. la toilette

    Richard Dunn

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    I was just going by the title, so someone should report this as wrong description title. AFAIK the Rega one is not as good as they made for sale under their own name but still pretty good and a lot better than what replaced it at Rega.

    I have a version with better bearings and a different method of setting anti-skate on my PL-71 and that will track anything just by adjusting mass in the headshell and the counterweight. I track SPU, Decca, DL103 and what ever I try.

    SpeedySteve has done a twelve inch version of this arm and has said it is very good, there is a thread on DIY. He has also done a 12 inch version of the PL-71 arm so I got him to do my spare, it looks very good and is waiting to go on a 401 I still have to plinth. As I understand it with high mass requirements the anti skate is redundant. I also seem to remember the part is available.
     
    Richard Dunn, Aug 12, 2010
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  9. la toilette

    sq225917 Exposer of Foo

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    Off.

    I was once shown a good check for tonearm bearings requiring nothing more than a sheet of printer paper and a pair of scissors.

    Cut a 5cm wide strip from the long side of the paper. Cut this into 0.5x5cm, 1x5cm, 2x 5cm, 3x5cm etc sections.

    Then balance the arm so it is free floating vertically with anti skate turned off.

    Then you hold a strip of paper between thumb and first finger, pinch no more than 1cm down the paper, and then use the bottom of the paper to try and push the headshell across the deck without bending the paper more than few degrees.

    A good gimball arm will go with the 1cm sheet, and a good uni will comfortably go with the .5cm. If it doesn't move with the 2cm then it's poor and if the 3cm can't move it then its knackered.

    it's a little easier than dismantling it for the swing test, which tells you little other than you have a heavy headshell.

    vid to follow
     
    sq225917, Aug 12, 2010
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  10. la toilette

    RobHolt Moderator

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    It stays at the level set when the belt disintegrated IIRC.
    Certainly one I looked a couple of years ago had quite high bias and the belt was caput.

    I have a nice R200 and the bias still works, so I've set it at 2g - right-ish for most cartridges just in case it snaps.

    Nice arm.
     
    RobHolt, Aug 12, 2010
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  11. la toilette

    sq225917 Exposer of Foo

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    sq225917, Aug 12, 2010
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  12. la toilette

    la toilette Downright stupid

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    The only reason I'm looking at Linn arms is that they have the same geometry as the original arm on the Lenco decks, so should drop in with not much messing around. The only others I have read that are close enough to avoid much alteration of the Lenco top plate is perhaps a Jelco arm, but I know little about them as yet, and there are fewer around 2nd hand.

    The GL75 I have is in very good original condition and because of this I wanted to avoid altering it if poss. Some people resort to cutting the corner off the top plate to accommodate other arms, but it doesn't look very nice. I also have a GL78 and GL72 and I intend to cobble together one good deck out of the two by putting all the best bits together - this deck I'm planning to re-plinth and modify so I'll have more options.

    That paper bearing test looks good, I'm not sure my last arm would have passed that :).
     
    la toilette, Aug 12, 2010
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  13. la toilette

    sq225917 Exposer of Foo

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    I'll ask Phil what milligram weight they equated to next time I see him.
     
    sq225917, Aug 12, 2010
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  14. la toilette

    TonyL Club Krautrock Plinque

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    Is the clunky old L75 arm in good condition? If so it would probably be worth replacing the no doubt perished rubber vertical knife edge bearings (third party ones exist that are far better than the originals ever were), locking out the saggy decoupled counterweight rod (apparently super glue and dental floss works a treat) and trying it out. It's not a great arm by any stretch, but I have a hunch it might sound half decent with a DL-103. It's certainly very high mass so you need a low compliance cart. Just check the lateral bearings are ok before wasting any time with it, they are pretty exposed so can get rather gunked up and sticky, plus the internal wiring is naff and the coating may have hardened up (it is remarkably hard to change, so I'd not bother). Plenty of excellent advice on this type of thing over on www.lencoheaven.net. If I wanted to customise a Lenco I'd prefer to use a replacement PTP top plate rather than cut up a nice one. Really clean and tidy L75s are getting much harder to find.

    Tony.
     
    TonyL, Aug 12, 2010
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  15. la toilette

    RobHolt Moderator

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    Simon, I'm surprised at you.
    Get those bolts sorted.
    Nice curvy Karma in a beautiful SME, and horrible skanky looking bolts.
     
    RobHolt, Aug 12, 2010
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  16. la toilette

    la toilette Downright stupid

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    That's exactly it re the GL75 Tony; it's in top condition and it seems a shame to chop it. Maybe it could be worth playing with the original arm (yuk) - it's in clean condition to look at, but feels a trifle 'baggy' :D. The counterweight is better than the one on the 72, but still doesn't look or feel right. I have a DL160 I could try out on it if I get it sorted.

    The other ones I have is the 72 which is also pretty tidy, and I've just picked up a tatty 78 which I'm planning to rob of its platter and spindle to mod the lightweight platter-ed 72 into a heavyweight. The 72 has a flat top plate that looks simpler and nicer, and the speed controls are better placed. I'm planning to rotate the deck 90 degrees in a new plinth so that I can mount any arm I like.
     
    la toilette, Aug 12, 2010
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  17. la toilette

    TonyL Club Krautrock Plinque

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    Sadly the 160 would hate it! It's a highish compliance cart and the L75 arm apparently has a huge 23g effective mass. This pretty much limits it to high-tracking DJ carts or a 103 these days. An AT95E should probably work ok too, but I suspect a 103 is the best cart you could get it to take.

    The 'baggy' feel will be down to perished rubber 'v' blocks. Replace them with the third-party hard plastic ones and it will be better than new. It's an easy job and IIRC the new v blocks are around £15.

    Tony.
     
    TonyL, Aug 12, 2010
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  18. la toilette

    la toilette Downright stupid

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    Just ordered replacement v blocks; at such relatively small cost it's worth a try before I dismiss the original arm.
     
    la toilette, Aug 12, 2010
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  19. la toilette

    sq225917 Exposer of Foo

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    Rob, what's wrong with my cartridge ears?

    You should know me better than that, looks is hardly on my consideration list.
     
    sq225917, Aug 13, 2010
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  20. la toilette

    speedy.steve

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    The belt on my RB200 Acos arm was long gone - failed with antiskate off - at least it did not drift when balanced, perfect for a 12"...


     
    speedy.steve, Aug 14, 2010
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