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Dual 506-1 issues

Hanspecans

Hanspecans

Member
I know there are multiple threads about this unit but they haven’t been updated in over 10 years. I posted to one here but no traction.

'Grounding issue with a Dual 506'
https://audiokarma.org/forums/index.php?threads/grounding-issue-with-a-dual-506.351840/post-17324595

You can read there also but basically I am hunting down a LOUD hum that (usually) hits the right channel. Powering down makes it go away. Sometimes I won’t have this issue for days or weeks. Sometimes it’s twice in a night. Very random.

Today I did take the unit apart thinking I would replace the RCA cables with some old component cables. Once I got in there I realized I could not figure out how to get the bushings that thread the wires onto the plinth off. So that was a big non starter as I didn’t want to destroy them.
Also I realized that these component cables are so much thicker than the existing cables and I would have a hard time threading them anyway.
I also took a look at the soldering from the very tiny tonearm wires to the RCA connections and they seem fine.

So I’ve let this be for now.
I also have a DIY counter weight solution with a screw and washers that I have been using for years. Luckily it seems the balance is still ok after doing this recent operation. I did order a new one finally from DualFred.

Anyone have advise for getting those bushings off or if this Loud hum is from something else?

Thanks!
 
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The hum is due to a bad connection somewhere between the pins of the cartridge and the RCA plugs, or it could simply be a bad connection of the ground wire.

I would not replace the RCA cables unless they are damaged, more than likely they just need to have the RCA connections cleaned and solder connections touched up.

Some useful tools when working on turntables are:

Soldering iron
Digital Multi-Meter or Continuity Tester
Jeweler's Paste for cleaning carbon deposits off of signal connections
 
I suspect that you are right. I was having major issues with no sound coming through either channel when I reassembled and I could only get it back by wiggling the cartridge.
 
I worked on this a little more today. I would have taken pictures but I could not get my phone to focus so closely since I didn’t want to remove the tone arm completely.

I don’t know the names of these parts but I will do my best. I took the cartridge out from the head shell and noticed that the plate that the wires are connected to in the head shell was very loose and would come all the way out or move back and forth easily. I took a a guess that maybe this is why channels seem to go in and out when the cart / headshell is touched / wiggled. Just in case I cleaned the contacts and used a little tiny piece of double sided tape to keep the plate from moving so much.
I also cleaned the contacts on the cart and made sure the wires seemed secure.

So far so good but it’s such a random thing I won’t be surprised if it comes back.

I’m eagerly awaiting the counter balance from dualfred since I am sure my very incorrectly and not properly balanced DIY solution is not helping.
 
another slight update while awaiting on my counter balance to arrive.

I finally got a tracking force scale and saw that with my janky eye balled set up using a DIY counter balance I was tracking at around 4g.

The ortofon DN155E tracking force is suggested to be 1.5g.
Getting as close as I could and not at all zero balanced properly I got to around 2.15 tracking force.

The beginning of LP’s were sounding great and the inner groove distortion was HORRIBLE.
Also when setting the anti-skate to match the 2g tracking force on the elliptical side, the record would still skip.

I did a bunch of trial and error and it turns out that if I add 2g via tone arm balance adjustment the inner groove distortion completely goes away. I’m not sure if the extra weight helps because this is an old stylus but it is a night and day difference.
Also the only way I can stop records from skipping towards the end was to do a counterintuitive setting of 1 on the spherical side of the anti skate.

So that is all for now. Basically I made no progress but learned some interesting things for when someone else is looking on the internet for info about this in the next 10 years.
 
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My legit counterweight had arrived from dual Fred and I immediately got to work zeroing out the balance of the tonearm.
When zeroed out and then adding 1.5-2g via the tonearm adjust and elliptical tracking adjustment records sound very nice at the beginning but just as before with my DIY counterweight there is a lot of inner groove distortion.

The ortofon DN155E tracking force is suggested to be 1.5g. but it just can’t seem to get away from inner groove distortion unless I go up to around 4g tracking force. Is this normal for an older stylus or indicative of something else?

I may ask this question more generally in a new thread since it seems no one is clicking on this due to being a Dual 506 thread title.
 
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