Rockola Tone Arm Counterweight

Rob what oil do you recommend for the bearings? I've used 3 in 1 motor oil like I do for the rest of the mech but wondered whether I'd need something lighter

It does sound great at present but I do see the stylus moving to the side on slightly off centre pressings as per below:

http://youtu.be/XS2AzAy3SoI

I apologise for the choice of music in advance!! It belongs to my other half

Though the movement is not terrible I will do some experiments this evening to see if I can reduce it at all. I'm thinking less weights to produce the same downforce, I may even weigh the arm and the additional hardware to see exactly what weight is being added. It may seem excessive, but hey, everyone has to have a hobby!

That is a fair amount of wobble. I can't really draw a comparison because I always used a Pickering DAT (automatic t-t) model stylus and these are inherently a bit stiffer. All later models of Shure styli tend to have longer, thinner cantilevers and be a bit 'floppy" especially the low-VTF models.

The 'test" I used on arms is to set it to play mode with no record and lift the forward area of the arm with the top of your thumbnail and see if it will track across with out slipping off. You'll have to allow some resistance due to the trip contacts but the play grooves should be reasonably free.

If you have a Neuses gauge you could free balance the arm then actually measure the friction in grams (if any).

As a rule all mechs were taken apart and bathed removing all old oil including that from the arm bearing well. I used a light sewing machine type oil, but later found that the same 20wt I used elsewhere on the mechs was OK too.

Another area to check is the tonearm wire. As I mentioned earlier I made sure they had no outer covering and didn't drag on anything.

Beyond that, if it isn't groove hopping I wouldn't worry about it.

Rob

The tone arm cable has braiding on it up to the point where it enters the clamp on the tonearm assembly. I've routed it as best I can, which seems to be down the back of the assembly - when looking at the back of the tonearm the cable comes down to the right of the screw that hits the trip contacts. It seems to move freely, if you know a better way to route it I may give that a try.

Should the bearing well have a lot of oil in it? All I did really was clean the shaft that goes into it, then put some drops of oil onto it and put it back. I did also oil the circular surround at the top of the well as per the lubrication chart

Psychman wrote:The tone arm cable has braiding on it up to the point where it enters the clamp on the tonearm assembly. I've routed it as best I can, which seems to be down the back of the assembly - when looking at the back of the tonearm the cable comes down to the right of the screw that hits the trip contacts. It seems to move freely, if you know a better way to route it I may give that a try.

Should the bearing well have a lot of oil in it? All I did really was clean the shaft that goes into it, then put some drops of oil onto it and put it back. I did also oil the circular surround at the top of the well as per the lubrication chart

As it ages, most wire insulation becomes "stiff" due to the leaching out of chemicals used to make it flexible.
New wire certainly doesn't hurt.
At the rear of the arm, proper "dress" of the cable is also important.
The secret here is to "loop" or "coil" the cable once from the arm to it's anchor on the chassis.
This increases its "bending" flexability, reducing any resistance of the arm's movement.
As for the pivot shaft - cleaning, perhaps careful polishing/buffing of the shaft and bearing along with a fine light oil sparingly used would be in order.
Zoom Spout Turbine Oil is excellent for such uses. - just a "smear" along the shaft pin is all that's needed.
If the pivot pin rides on a ball at the bottom of the shaft - a drop of oil on it.
If it rides on the top of the shaft, perhaps on a thrust washer - polishing all contacting surfaces is good, or changing the washer with a Teflon washer is a good idea.

Again, the ratio of downward force as opposed to lateral friction is important here.
We want to keep the stylus tip planted solidly down in the groove to reduce wear.

My tonearm cable has 2 forked pieces on the screened section for grounding. One is clearly meant to be attached to the amp. Any ideas where the second one is attached? I'm still not 100% what path this cable should take when it leaves the rear of the tonearm assembly and this may make it clearer for me

I tried different combinations of bolts and washers and managed to achieve the same level of balance with less overall weight added to the assembly. I still got excessive wobble on the n44-7 stylus (at 2.5g), so until I can test other carts I've put the "jukebox" stylus back on and set the tracking weight at just over 4g, which is half way between the 3-5g recommended weight, seems to work ok and is an improvement over the excessive weight added by the spring.

This may also be a shot in the dark but would anyone know the specs of the screws used to mount the shure cart to the tonearm? One of the heads has worn away completely so may make it tricky to remove this shure cart now!

This is a great mod for rockolas. I did my 454 and it is tracking about 3 grams and I think it sounds better than when it was tracking about 5 grams. Very stable and easy to do. Now has anyone got pictures of a mod for wurlitzers. I have a 2810 with sonotone 9t cartridge and I would like to change it to magnetic cartridge and lower tracking weight.

Canadian, there really isn't much to be done with these arms, they have primitive bearings and a lot of mass.

I converted all of the carousel Wurlitzers that I owned and sold to use a Pickering magnetic. here is what it looks like in the later arm:

http://s1192.photobucket.com/user/Rob-N ... rt=2&o=210

http://s1192.photobucket.com/user/Rob-N ... rt=2&o=211

Beyond that I check that the lead dress does not cause bias and flip the keeper on the trip switch to place the whisker constantly against the tail then rebalance the arm to compensate for this load.

You can experiment with a gentler trip switch and relay combination as I did, but I didn't find much benefit.

With the above, reliable tracking @3gm VTF is achievable. I used a 2400s on location for a year with no problems.

Rob-NYC

Hi Rob
Thanks for the reply. I take it the cartridge fit ok and how did you rebalance the tone arm. Was any counterweights required? Did this mod improve the sound and is it worth it? I have a 546 amp so adding a preamp is simple.
Thanks
David
Ps sorry for getting off the topic of rockolas.

David, the magnetic that I used was slightly heavier so sometimes it was necessary to add a bit of extra weight to teh pocket on the tonearm:

http://s1192.photobucket.com/user/Rob-N ... rt=2&o=115

The large screw is the fine adjustment and coarse is done by adding weight to the pocket just to the right of it. It was not always necessary to add weight as the weights Wurlitzer used varied in size. When necessary, I just glued in a bolt.

The question as to whether it will really improve the sound is relative to what else you do at the "other end" -the speakers. I added a 6db crossover consisting of a suitable choke for each woofer and simple capacitor on each for a horn tweeter on the channel opposite the one with the 7" mid. I generally modified the preamp to add about 6db more treble rising above 6KHz. That combination makes an enormous improvement in the sound. It essentially takes these from being fairly crude sounding phonos designed to cover up worn records and styli and in noisy commercial environments and makes them more enjoyable in the home.

Rob

Rob
I knew you would have done this on a Wurlitzer and would have photos.
I was looking at your photobucket pictures and saw that one but was expecting a lot bigger weight and only checking it again saw the weight. I have ordered an older pickering cartridge and I think I will try it. I have read some of your posts about the crossover and tweeter
and I think it might be worth it. Would be interested in any info on the crossover and tweeter you used.
Thanks
David.

David, re; crossovers, I reused various chokes from both speaker and other applications for the crossovers. When i ran out of those I bought 1.2Mh chokes from Radio Shack...an option that probably no longer exists. Here is a chart that will help in selecting values:

http://www.parts-express.com/resources- ... tion-guide

If I am not mistaken, one of the 12" speakers in those machines is 8 ohm and the other is 16 ohm. Measure the voice coils to determine if that is correct and then adjust the values upward in Mh for the woofer choke if it is 16ohm. An 8 ohm speaker will measure approx 6ohm on your meter and a 16 will be around 12-13..

Rob

Rob
You are right on with the speaker resistance. One 12 inch is 16 ohm and one 12 inch is 8 ohm, the third one is 6 inch 8 ohm.
According to the manual it says on 12 inch heavy duty speaker, one 12 inch mid range speaker and one 6 inch tweeter with a
cross over network. Would any thing be required on the backend or would this be sufficient. I only can find a 4uf cap on the six inch speaker. Should I still add an additional crossover?
Thanks
David

David, my approach with these machines where all speakers are in a common acoustical environment is to treat it as one monophonic speaker.

So we have two 12" woofers that are voiced slightly differently with one channel having the 6" midrange as well.

The single capacitor on the mid constitutes a typical 6db/octave 'crossover" and this is an adequate approach for these situations. I suggest adding another -real- tweeter to the other channel and adding a choke coil to each woofer to get the highs out of them. Speakers larger than 4" are really not suited to reproduce high frequencies and in the case of 12" speakers the result is a sort of 'cry' and smearing of the sound as the speaker can not react fast enough to reproduce high frequencies.

Using the table i noted above I would select approx 1.2Mh in series with the 8 ohm woofer and use approx double that value for the 16 ohm woofer -although these values don't have to be set in stone. That is you could use the same choke value for the 16 ohm and realize that it will be 6db down a bit earlier. I've never been too strict about these values, rather just based my choices on what I felt sounded good...and what i had on-hand.

The tweeter should be quite efficient. This one is similar to what I have always used:
http://www.pyleaudio.com/sku/PH25/3-x-3-Horn-Tweeter If the highs prove too hot for your taste you can pad the tweeter down with resistors or just turn down the treble control a bit.

Rob