Dual 704 dead (counter)weight

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minerwerks
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Dual 704 dead (counter)weight

Post by minerwerks » 20 May 2015 04:41

This seems to be where I always locate answers regarding my Dual 704, so I'm hoping you folks will be able to help me weigh the options regarding my anti-resonator counterweight.

Back in this thread:
https://www.vinylengine.com/turntable_f ... hp?t=31587
I learned how to take apart my counterweight.

Now, my anti-resonator weight suffered from the problem of sitting detached in the cradle (I found it like that years ago). I took apart the counterweight assembly and found that the spring strip (under the red arrow in the below image) had a clean break where it continues over to the plastic clip.

http://imagizer.imageshack.us/v2/450x30 ... nator2.jpg

I took a picture of my weight and clip then highlighted in red where the spring strip is.
tube.jpg
(62.81 KiB) Downloaded 918 times
I had heard that some people had replaced the strip with a similar part from inside a tape measure. I figured I might be able to fashion a rough replacement myself.

The problem is that I could not figure any way to remove the longer part of the spring that is still inside the weight/tube. There is a rectangular nut above the strip that holds it inside the weight (notated by the red arrow in the earlier image), but as far as I can figure from the exploded diagram of the counterweight, the screw that holds on that nut is INSIDE the shell of the weight. I pried a bit along the edges to see if the interior section would slide out of the shell, but it seems to be glued or cemented in there. Without that screw accessible, there is no way that I can see to loosen the nut and remove the broken strip. I am assuming it is not possible without surgery to the weight and/or its shell

My other thought was to try to solder or bridge the two parts of the spring strip back together, but that's beyond my level of experience. Brief attempts to put solder over the broken seam were miserable failures.

What I had been doing, until I was willing to tackle a possible repair, was to wrap the weight in a thin elastic hair tie, thus isolating it from the outside of the plastic cradle where it would normally just rest loosely. I just read of someone using silicone adhesive to mount the weight inside the cradle permanently, but I'm not sure if that would be preferable. I assume the silicone was chosen to give some dampening to the weight rather than locking it down with a stronger adhesive.

I would be interested in buying a new old counterweight, however I don't know how long I'd have to wait for a 704 version to be available somewhere like eBay. Suggestions for close matches that would still be functional and slide into the tonearm would be welcome.

So there's where I am at. A few options, not sure of which is the second best (behind buying a unit specific replacement). Looking for suggestions on what I should choose to do.

Next task: repairing the anti-skate cam wheel!

Tinkaroo
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Re: Dual 704 dead (counter)weight

Post by Tinkaroo » 20 May 2015 10:08

Trying to repair it would be a very difficult task, and it probably would not be the same as it was originally engineered either.

I think it would be a lot easier to find a used one on ebay, but you may need to be patient.

I was looking for a replacement for my 604 or 621 and found a 704 counterweight. The 704 uses the exact same counterweight as the 721.

The topic was discussed here.

https://www.vinylengine.com/turntable_f ... t&start=15

minerwerks
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Re: Dual 704 dead (counter)weight

Post by minerwerks » 20 May 2015 15:01

Tinkaroo,

Thank you for the reply. I had indeed skimmed that thread - it came up in my searches since you had found your 704 counterweight and posted a picture.

But since the rest of the discussion focused on some different models, I had overlooked information that I was now asking for. Namely, I could probably put a counterweight from a 604, 621, 701 or 721 on my 704.

While somewhat tacky considering the great piece of equipment that the 704 is, I would be curious what people think about the options for basically mounting the weight back to the cage, whether by silicone adhesive or by the method I used of filling the gap between the cage and the weight with an elastic hair band. Having already lost any of the anti-resonance properties built in to the assembly, I would just be minimizing the effect of the weight vibrating loose in the cage, as far as I know. Obviously, this adds some weight to the design, but I would think this is mitigated by the fact that the counterweight is adjustable. If it introduces any new issues to the sound, I could not even begin to guess what those may be.

= Derek =

minerwerks
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Re: Dual 704 dead (counter)weight

Post by minerwerks » 20 May 2015 15:09

I did see this counterweight on eBay that is supposedly from a Dual 1246, but it looks exactly like the 704 counterweight. It appears to have the same problem as mine, however, where the spring has snapped and left the weight sitting loose.
http://www.ebay.com/itm/Vintage-1976-Du ... 487eaecf14

But it does suggest the question of whether there is another series of tables with the same or similar counterweights that would allow a broader search for a replacement.

Dualmaniac
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Re: Dual 704 dead (counter)weight

Post by Dualmaniac » 20 May 2015 17:02

Hi,
Your counterweight part number is 239 420. It is indeed the same as the 1246, and probably some others in that similar time frame. The 1245 counterweight 236 904 is slightly different, but "mostly" compatible. I am not sure if the resonant frequency is exactly the same, but it fits. And the 1245 / 1246 are almost identical. (I have a one-of-a-kind 1245.2)

dualcan
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Re: Dual 704 dead (counter)weight

Post by dualcan » 20 May 2015 17:09

The only thing to do is, as Tinkeroo stated, and to find a non-damaged replacement.
These units can be repaired but even if you had the original spring steel part as a replacement, you still are out to lunch, unfortunately.... This is because once the anti resonance system (weight) was manufactured, it underwent resonance tuning with sophisticated measuring equipment and the necessary generators.
BTW the resonance of any ton arm must be between 8 and 15 Hertz. the trick is to achieve this window taking into account the complete mass of the tone arm.
Without this tuning, the weight will work but the anti resonance feature obviously can't work.
Regards,
k

calgarysaurus
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Re: Dual 704 dead (counter)weight

Post by calgarysaurus » 21 May 2015 04:52

I have a spare 721 counterweight. If you are stuck, maybe I can help you.

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