Rewiring a Rega RB250 - diyAudio
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Old 1st August 2006, 02:23 PM   #1
serse is offline serse  France
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Default Rewiring a Rega RB250

Sounds like an old story, but...

I am intending to rewire a RB250 with the Incognito kit. Lurking around, I found this paper which seems of some interest :
http://www.tnt-audio.com/sorgenti/analogue_bits_e.html

But I also found this one and got a bit puzzled by the warnings :

http://www.william-reed.net/audio/rega1.html

I've noticed that according to the first author, rewiring a RB300 and a RB250 seems to be slightly different ; I quote :

"Having the main tube apart allows easy access to the tiny hole the wires are supposed to go through. Believe me, this sure beats messing around with a pull cable (as still is required for the RB-250, by the way!)"

So... Can I apply the first procedure to the RB250 and remove the arm tube ? I wouldn't want to destroy the bearings in the process, even though I don't really see where is the problem...

Thanks


Pascal
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Old 1st August 2006, 02:55 PM   #2
sreten is offline sreten  United Kingdom
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Hi,

the procedure for removing the arm tube in the first post
can't be applied to a RB250 as the yoke is very different.

/sreten.
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Old 2nd August 2006, 03:56 AM   #3
serse is offline serse  France
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Ok, thanks Sreten. Seems I will have to play with a kind of "fishing" wire...
Hope the result will worth the hassle !

Pascal
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Old 2nd August 2006, 09:39 AM   #4
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Hi, that second link is mine, and I really do recommend not taking an RB250 apart!

The very easiest way is to prepare for the re-wiring *before* you remove the old wire. Tie some fine thread to the old wire and pull it through, then you have the thread ready to pull your wire through with.

If you have to start with a bare arm, then the best method I've found is to strip a single core of Cat5 wire which is about the right stiffness to thread through. With the stub out, you can start at either end, but the base is easiest.

Once the Cat5 is through, you can either solder the wires to it and pull them through from the base, or use the Cat5 to pull some thread through and use that to pull the wires. I find the second method can work best.

If you're using the Incognito loom, you'll only have to do the cartridge tags as all the rest of the work is already done, so it's a fairly easy job.

regards, Jeff
PS, Although the RB300 just unscrews, the bearings were originally set up using a jig and there's no really accurate location for the two bits of Yoke (like dowell pins) so the chances are that you may not be able to replace them as accurately as originally. Bearing alignment and loading are really critical to performance.
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Old 2nd August 2006, 12:12 PM   #5
serse is offline serse  France
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Hi Jeff,

Thanks for your comments. Actually I had a slightly different method in mind : I was intending first to remove the existing counterweight and stubshaft (as I have to do it in order to install the Michell TecnoWeight...), then to introduce the Incognito wire from the base, to get the wires from the rear of the arm and to pull them (gently) along the tube with a very thin stick of bamboo (as suggested by someone ).

What do you think ?

Regards

Pascal
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Old 2nd August 2006, 12:47 PM   #6
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Hi, It might be hard to get the wires up the vertical tube from the base by pushing rather than pulling as they'll tend to bunch. Also, there should be a tiny rubber grommet at the top of the tube making it much more difficult (but that often gets displaced when de-wiring the arm. Pulling through on thread or wire is very easy once you have the thread in place and there's very little chance of damaging the very delicate wires.
regards, Jeff
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Old 2nd August 2006, 06:08 PM   #7
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Ive been wanting to take my rb250 apart for a while so i can strip and drill the arm tube.
What is so difficult about taking them apart?
Ive read your warnings but dont see the problems as ive never tried.
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Old 2nd August 2006, 06:23 PM   #8
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Not sure whether you've seen this: http://www.hi-fi.com/diy/rega/steps.html

I rewired an RB250 using these instructions with no hassle.
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Old 2nd August 2006, 10:32 PM   #9
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"What is so difficult about taking them apart?"

Nothing hard about taking them apart, just putting them back together as you will definitely ruin the bearings and damage the brass stubs.
I've done six RB250s and never been able to get those stubs out without damaging them. They are in very tight and the brass is very soft, so you damage the screw slot badly. Unless you can devise and make a rather precise little puller to act only on the outer race, you have to drift the bearings out, which seriously trashes them.

The yaw bearings in the brass body can usually be left in place whilst their shaft is taken out, but replacement is so easy you might as well change them. Alignment and loading of the bearings is *very* critical, as I've found to my cost and there's not really a chance to adjust them afterwards. I really wouldn't want to tackle setting up new bearings using the standard Rega location method. I now make every component from scratch keeping only the arm tube, 'cos proper bearing location is easier that way!

Replacement bearings are about 4 each from RS components and all 4 are the same. do resist the temptation to try high-precision bearings in standard Rega mounts as the location isn't accurate enough for them and the results will be far worse than ABEC3 bearings. The RS ones are ABEC5 which is a bit tighet for this application, so running them in well before installing them is well worth the effort.
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Old 3rd August 2006, 09:15 AM   #10
serse is offline serse  France
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Hi Jeff,

I had a look on your site. Quite impressive. I like very much your counterweights, especially the low-cg one.
Is it just a one-shot project for your own personal agreement or do you intend to offer some of these modifications on a (even informal) commercial basis ?

Pascal
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