Headin' back to the 50's ... with a Bogen Lenco B50-16

[kenwood61]

I just want to applause a stellar, solid restoration job bringing this turntable back to life!
 

Thanks for hangin in there with me 

[kenwood61]

The manual says "No other ground connection should exist".  If you have mains safety grounding, it will exist.  I guess that when the manual was written, normal household gear didn't have safety grounding. Run the signal wires from L+R and G+G and connect the earth wire to the metal of the tonearm.  Then you should be hum free even when using modern electrical safety precautions.

First question on the headshell. It sounds like I am removing the ground wires and just using the R channel as "hot" and L channel wire as "Ground" ... which would require a second jumper clip (see extra one I have in photo).



More pics of the tonearm.

Here is view of 3-pin connector.



This shows braided tonearm wire simply passes through tonearm base underneath to terminal strip. Earth wires are connected to tab on tonearm post (part of arm chassis) and base, which screws into deck.



Terminal strip with tonearm wires, tonearm ground wires, and external ground wire to preamp, all connect.



Maybe not necessary, but here is mains wiring to motor and top plate. I'm using a 3-prong grounded ac cable, so all three tabs on the IEC chassis jack are connected. L, N, Earth (Ground).

[Nordfinn]

I hope this is not too far off-topic, but I found the diagrams available on this Ifi page very helpful in explaining ground loops, and in convincing me that I had indeed introduced one too many grounds with the addition of a mains ground to a vintage component: https://ifi-audio.com/home/computer-audio-tutorial/grounding-diagnostics/

[kenwood61]

Looking at it .... it would appear to suggest that since my amp and turntable both have grounded mains, that is my problem. BUT, I have other turntables, also with 3-prong grounded plugs and no problems. They are all plugged into a Furman PST8 power strip.

Observations of changes that did not get rid of hum:

• removed headshell, powered up, still hum ... does this mean headshell is not contributing, or simply what to expect with no headshell/cart connected?
• turned amp off, and listened in preamp with headphones
• pulled ground wire off amp

I'll have time tomorrow to get to this. Thanks for the help.

[Kno]

Is this thread relevant, referring to double grounds etc

https://www.lencoheaven.net/forum/index.php?topic=14518.0

[kenwood61]

Is this thread relevant, referring to double grounds etc

https://www.lencoheaven.net/forum/index.php?topic=14518.0

Interesting ideas in there. I think part of what my brain is trying to wrap around is that some pins on a cart are not used. And being used to stereo operation, doesn't make it easier to grasp.

It also seems that keeping the ground configuration of the mains with top plate and motor earthed are safety-related, whereas there are no safety issues with how I ground or don't ground the signal path, correct? If so, I will try changing the configuration of the wires in the headshell only, at first and see how that works. That will have to come later today after work. We'll get this figured out today. We must before it's time to spin some vinyl tonight and get some video!!

[kenwood61]

Signal ground is connected from cart/headshell to terminal strip, where the tonearm is also connected. So I have two ground paths that are connected at the preamp ground post AND the outer sleeves on the RCA connectors. Even if I pull the ground lead at the preamp, I get hum.

The "ground" tab on my terminal strip has ground from headshell, tonearm, and shield on phono cables, and separate ground wire to preamp. Should I move connections on terminal strip so that L+R is on the same tab, shield ground from phono cables connects a tab with G+G from headshell, and the 3rd tab just be tonearm to ground wire to preamp?

[niclaspa]

The "ground" tab on my terminal strip has ground from headshell, tonearm, and shield on phono cables, and separate ground wire to preamp. Should I move connections on terminal strip so that L+R is on the same tab, shield ground from phono cables connects a tab with G+G from headshell, and the 3rd tab just be tonearm to ground wire to preamp?

Yes, that should avoid creating a ground loop.

[kenwood61]

I'll give that a try in the morning after coffee and breakfast, thanks 

[kenwood61]

Nope, no change. I'll look at this again tomorrow. I can tell you that if I touch parts grounded to the mains, I notice a little jump in hum ... I'm really thinking I need to remove the earth from IEC plug, top plate and motor.

[Montvason_paul]

Can anyone recommend a quality replacement rubber/silicone tire for the idler wheel? I see one on the auction site that is a translucent yellow/amber ...

Change it out for a later Lenco wheel.
This is what you will need.
3mm drill and some thin 3mm packing washers.
You drill the phosphor bronze bearing out to 3mm in the later Lenco idler to fit the early idler wheel spindle. Use the packing washers to position the new wheel correctly. There are 2 nuts on the old spindle to check the play of the wheel, tighten up just so.
I actually drilled mine with a battery hand drill but the trick is to not push and let the drill but do the work. Make sure to put some thin grease on the spindle a very small amount.
Hey presto modern idler wheel on old spindle and no noise.

[Montvason_paul]

Here's my listing of essential items that I think I need. Don't need "new", but just clean examples.

1) safety capacitor for motor ... I have this!



2) new bakelite 3-prong plug that fastens to the tonearm, and the headshell connects to

3) new idler wheel or just new rubber ... I can see nicks out of it, although I'm guessing it will run just fine as is

4) need a new power switch ... the lever on mine broke off

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Questions:

1) do I want the N7D stylus for the SHURE M7D cartridge that came with the deck, or try and find an N21D for lighter tracking force?

2) do I replace the platter mat? I can always do later ...

3) do I need one of Werner's thrust plates? since this is so light, I'm thinking not

4) can I straighten the main bearing without breaking?

5) source for good mono wiring so I can rewire tonearm ... may not need, but I like doing this

6) speed selector plate ... try to clean off rust and hope I like, or get replacement? since I hope to refinish original paint on top plate, doesn't make sense to get shiny perfect and new.


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I'm sure more questions will pop up as I get into this, including what kind of plinth will I make and out of what kind of wood. I think I'll get the table working and done, and then based off what I hear, will decide.

I will add rca chassis jacks and a grounding jack ... or I may tie ground into the right channel jack. Probably keep the original power wire since it's in good shape. I have IEC chassis jacks from Schurter as well as 3-prong power cords.

The Bakelite tone arm broken bit, believe it or not if you are very careful and you have both bits a good quality superglue will do it. After you glue clamp together gently and make sure it’s lined up correctly and walk away for a day. There should be a long silver screw that goes through the tonearm and a plate then a nut. There is also a small separate screw. The switch is easily obtainable and I’ll look tomorrow see if I have a spare. I’m buying these decks up like they are going out of fashion. Infact I drilled a top plate and put all the gubbins in so I could drop the tonearm with the guide on one of mine. Look at my post from today about Art Deco DJ decks.

[kenwood61]

Thanks for the info Paul. I do have a new idler wheel that works great and new 3-pin connector. I did not throw out the original and may glue it up just to have.

The only issue I'm having in completing this project is wiring configuration. I'm getting a hum, that includes additional rise with touching parts earthed to the mains. My current setup is a 3 plug IEC chassis jack with Live, Neutral and Earth. Earth is connected to motor and top plate.

[Montvason_paul]

Thanks for the info Paul. I do have a new idler wheel that works great and new 3-pin connector. I did not throw out the original and may glue it up just to have.

The only issue I'm having in completing this project is wiring configuration. I'm getting a hum, that includes additional rise with touching parts earthed to the mains. My current setup is a 3 plug IEC chassis jack with Live, Neutral and Earth. Earth is connected to motor and top plate.

Sounds like a ground loop hum, you may just need to remove one earth at a time and see what that does. I use shielded neutral and live wire on mine and no hum. I also have two of these decks side by side and a whole lot of other bits in the box. With mine I get a little white noise but pretty sure that’s the old vintage switch I’ve used and the valve amp is 2 x 40 watt.
Paul

[Montvason_paul]

I’m pretty sure the plate on the tone arm underneath is wrong. It’s the correct plate but it’s the support plate for the Bakelite connector. The big silver screw goes through it with nut. The other bolt goes through the hole underneath and the cut out on the side is for the tonearm wire from every B50 I’ve seen.
Paul