DIY Rega arm conversion kits
| PARTS | TAKE APART | DISMANTLE BASE | REMOVE/SERVICE ARM LIFT | THREAD SIZES |
| MOUNTING TEMPLATE | WIRING CONNECTIONS | BEARING DETAILS | ARM TUBES | THEORY |

An RB250 arm
taken apart

New repair kits
The most effective way to rebuild stiff bearings or broken parts.

1-Armtube   2- Vertical (pitch) bearings, brass bearing carriers and covers
3- Arm yoke  4- anti-skate magnet  5- Bearing spindle 
6- Base with horizontal (yaw) bearings 7- Arm lift parts 
8- Cover for anti-skate mechanism 9- Adjusting magnet for anti-skate 
10 - Arm rest

RB300 parts differ

Rega have not designed these arms to be taken apart, serviced or adjusted. if you dismantle them in any way, you do risk ruining the arm.

If you’re installing one of our kits, the cautions here don’t apply as you don’t need to save any of the parts except the armtube, arm lift and arm rest.

NOTE: if any of these parts don’t want to move, the locking glue will be the problem. It can be softened by heating but that might ruin paint and small rubber parts. Acetone (or nail varnish remover) will also soften the glue.
CAUTION: the plastic antiskate adjuster cover is easily broken. Don’t apply force!

We recommend that you DON'T dismantle a working arm just to rewire it. This isn't necessary and it will almost certainly be worse than when you started.

TO TAKE APART
- Remove the wiring. You’re unlikely to be able to re-use this. The base plug is removed by removing the locking screw at the side of the base. It should pull out enough to gain access to the wires.

- Unscrew the counterweight stub. The thread of this is sometimes found cracked.

THE ARM TUBE

- Prise the two plastic covers off the arm yoke.

- Underneath are the brass bearing stubs. These unscrew. They will be very tight, especially on old arms, because they are glued in place. The soft brass screwdriver slot is easily damaged,

- The arm tube now lifts off.

This is a far as you need to go to rebuild the arm with one of our repair kits

You can usually perform the operation above and re-assemble the arm. In the next stages, the chances of damage are much higher. Only attempt this on an arm where you have nothing to lose!

Rega arm exchange
If you think your arm is beyond hope, exchange it for a Brand new RB251. For less than the price of many counterweight "upgrades"

DISMANTLING
THE BASE
- Remove the arm lift and arm rest first.

- Undo the two screws that hold the antiskate mechanism. These may be under plastic covers that look like part of the moulding. Just prise them off to access the screws. If this isn't done first you will almost certainly break the plastic cover when the shaft is moved.

- Holding the arm yoke, undo the nut at the base of the vertical shaft (5). This may be very solidly glued into place and refuse to budge. Don’t apply lots of force or the shaft may bend. Often the arm yoke comes off instead.

- If the arm yoke has come off the shaft you can remove the plastic parts. If your purpose was to replace a broken antiskate cover, then you are lucky! if it was for bad bearings then there is very little chance of getting the shaft out without damaging it. Time for one of these.

Only attempt this on an arm that is otherwise scrap!
REMOVING THE
SHAFT

- If the shaft nut has come off, the shaft and arm yoke can now be removed complete with the plastic cover.

The proper way to do this is with a little press tool with an M23x1 thread that fits over the base and a mandrel the correct size for the shaft. Without that specialist tool this method will work, with some risk to the shaft.

Put the fixing nut on to the base and put the nut back onto the shaft, just a few turns. Use the base nut to hold the arm in a vice and gently tap the shaft nut using a soft aluminium or wooden rod as a drift. Keep it square! The shaft should push out of the bearings. unscrew the shaft nut and pull the shaft out by hand.

You are now at the stage where the bearings can be drifted out and changed.

NOTE: The plastic cover can't be changed with the arm yoke fitted to the shaft. GIVE UP. The only reliable way to remove a yoke from a shaft is to support the entire length of the shaft in a 6mm lathe/milling collett, not a chuck, and unscrew the yoke. Any way that doesn't hold the shaft completely and evenly will almost certainly bend or distort it.

If the "wrong" part - arm yoke or fixing nut - has come off for the job you wanted to do, then there's three choices:
Repair kit
Exchange arm
Put all the bits in a bag an send it here

New Technics SL1210 version
a version of the micrometer arm built into a Technics adapter plate. A drop-in replacement

To remove the arm lift:
Take off the quadrant by undoing the small allen screw (A) about one turn. This is about 1.2mm, one size down from the smallest key in most DIY sets, so you may need to file down a slightly larger allen key to fit.

The arm lift is released by undoing its top plate (B). Small circlip pliers or snipe-nose pliers will fit into the slots to do this. Caution: there is a small spring inside!

You can read the full details for servicing the arm lift here from the Vinyl Engine site.

If your arm lift doesn't respond to the service procedure, we have complete Rega replacement units.

The mounting thread
and nut is M23x1
Not a common thread! A Rega dealer should be able to supply a replacement for a lost nut, or we can supply our own slim fixing nut.

Locking screw for the base plug.
Easily lost! M3x3 socket-head grub screw. A common item that you can buy from Ebay but you’ll probably have to buy 20!
Use a 1.5mm allen key to undo.

Cartridge mounting screws.
These are usually specified as M2.5 with 12.5mm centres. This is converted from the original RIAA standard, which was in inches. The screw should really be a “UNF No3” at half inch centres, which is almost identical.
Buy the length you want from any bolt specialist on Ebay rather than an "audio" source.

Counterweight stub thread
is M12 x1, a very common thread size. You will find correct taps and dies in almost any hardware store.

3-point mountings
The new mounting of the RB251 series.
The holes are based on a triangle of 36mm sides. This give a PCD of 40.2mm.

Mounting the arm
The mounting hole should be a clearance hole for 23mm, but you will find that most turntables with a "Rega" mount use 24-25mm for the hole, which works OK. The amount of clearance for the hole depends on the material and thickness of the mounting.
25mm is the maximum thickness that you can mount the arm onto.
Mounting template

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The earth connection is fixed to the arm with a small sprung plate behind the counterweight stub. It is terminated on the blue signal ground wire. Most people regard this a weakness of these arms.
A GR1 bearing can be identified by the stamped lettering on the shield. They are ABEC3

Current production 251 bearings look a little different from earlier ones although the specification is the same.

The bearings
The bearing specification for all the bearings is flanged, shielded ball bearing 6x13x5 with a 1mm flange. This is a very common size and should cost about £5 per pair.

Good quality replacements can be had from RS components:
http://uk.rs-online.com

part number 540-306

AFBMA Equivalent 628/6ZZ

Don't use a closer tolerance specification than the Abec5 type above. The arms aren't designed for it and performance will suffer.

The vertical (pitch) bearings of the RB300 series are different.

“All the arm tubes are the same."

NO!

Arm tubes for arms with a spring tracking force adjustment (RB300 etc) are not interchangeable with the RB250/251 type. They have a 12mm bore for the bearings rather than the 13mm of the RB250.

The current production arm tube has a thicker wall than the original by about 0.25mm. The surface finish of the tube under the paint has also been improved.

The Goldring GR1 arms
These are not the same as the RB251 arms, despite looking very similar. They were built down to a very keen price and the bearings are from a different source. Goldring bearings are the only ones that have stamped marks on the shields. They are of ABEC3 spec.

The theory and practice of setting up a tonearm

Downloads in
PDF format

Baerwald: "Analytic treatment of tracking error"
The Grand daddy of them all, the first analysis of the relationship between geometry and distortion. Just remember that the distortion data is based upon 78 records and spherical stylii.
Baur: "Tracking angle"
An early postwar treatment of the same subject with very useful calculations which show you the theory behind the conclusions.
Stevenson: "Pickup arm design"
This is regarded by many as the definitive work on arm geometry, from the 1960's.
Kessler & Pisa "Tonearm geometry and setup" (.zip file)
A work from the 1980's with the null point calculations updated for more modern stylus geometry. Probably the best and most understandable basis to work from. (the Kessler's not Ken)
Determination of sliding friction between stylus and record groove
R Pardee, Bell Corporation
The skating force phenomenon
J Kogen (Audio, Oct 1967)
Pickup arm design techniques
TS Randhawa (Wireless World, March 1978)
Sensitivity of Phonograph turntables to normal loads
TS Cole, (AES Journal May 1968)
A stereo groove problem
G Alexandrovich (AES Journal, Jan 1961)
The cartridge alignment problem – a new approach” RJ Gilson,
(Wireless World Oct 1981)

alignment protractor
An alignment protractor with alternative null points. Though the measurements are for Rega mounts, the nulls work for any arm.

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These DIY kits use the same parts as our complete arms and will transform a tired or broken Rega RB250

Full details

rb250 conversion kit Audiomods DIY kits will transform a Rega RB250, RB251 or Goldring GR1 arm in any condition.

Designed to be easily assembled without special tools or workshop skills.

Full details

The easiest way to restore a damaged RB250 arm is to drop the armtube onto one of our complete new bases.

If all else fails, exchange your broken arm for a new one

Rega RB251
November 2011 contact: jeff@audiomods.co.uk

5 Tormore Mews, Rectory Road, Deal, Kent CT14 9SX United Kingdom
Tel: +44(0)1304 379698