Grundig SO 151 US - Cleaning and Turntable Question

Rob_Feature

Rob Feature
My mom picked up this beautiful condition Grundig console this week from an estate sale and gifted it to me. She said the radio was playing while she was there, but she didn't think the turntable worked. Nice of her to get it, but now I'm diving into a new project to see what I can do, or whether I need to just take it in for repair.

First, since she said the radio was playing I felt like the amp/tubes/tuner were probably OK. Getting it home (after they transported it) I find that the radio 'sorta works'. I can tun in barely any stations and the volume/right/left goes kinda crazy when tuning across the dial or turning the balance/volume knobs.

This seems to me like either a reception issue (its got a built in FM antenna, but I need to probably figure out how to hook up a better one and see if reception is part of the problem), but also like it really needs to be cleaned. I think these knobs need a good detoxit.

But I need some advice on how I get behind the dials to clean this thing. I've got the back off so I can see the amp/tuner unit, but I hesitate to pull it out and clean it since I don't really know how it disconnects cleanly. Advice on that?

Second, the turntable doesn't turn on. In the pic you can see the knob labeled 1/2/3, and the 2 position is the 'manual' run position. But the knob is FIRMLY stuck in 3 (stop) position.

I haven't owned a turntable this old before...is there something I need to do to 'release' this knob (ie have something in a certain position) or is it just jammed? The whole turntable unit was pretty gooped up inside from lack of use...I gently manipulated the arm to loosen it up a little, but that told me it needs a good de-gunking.

So my 2 questions boil down to:

1. How do I clean the tuner knobs, etc (ie. how to safely remove the amp section for cleaning, disconnecting it from the front display)
2. Is there any magic ju-ju to get the turntable knob to turn to 'play' or is it just jammed? (ie. am I ignorant of how this works, or is it busted?)

Thanks in advance!
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The knobs have set screws in their edges. They need to be removed, then the chassis is screwed into the mounting board from below it. When free it will slide out backwards. Take many many pictures of how everything is connected. You’ll be able to deoxit from this stage.

The record changer’s grease has hardened. You will need to get a solvent into that switch mechanism, best done by removing the changer and flipping it over. The retaining screws will be visible underneath.

It will likely also need a retreaded idler wheel, which can be had from Voice of Music Audio Enthusiasts.
 
Thanks for all the info! I was thinking I might take a crack at this, but I've never worked on anything this vintage and I'm afraid I might do more harm than good. I think I may just bite the bullet and take it into my local audio guru shop tomorrow...the price hurts, but I know it'll be done right.

This info helps me know what might be involved, though...I'm afraid what a rehab might cost, but the thing is beautiful...I can't bear to leave it in the state its in. Thank you!
 
Oh, and does anyone have info on approximate year of manufacture for this? I wasn't able to find much, with my best guess being 1959/60 or somewhere around then?
 
Well....so much for that. I called a local shop here in metro detroit that I always take stuff to...they're hesitant to work on it, and it sounds like it'll cost a fortune. I guess I'll be trying to fix it myself afterall :)
 
The knobs have set screws in their edges.
Found the 'outer knob' set screw and took that one off...but can't figure how the secondary knob behind the outer knob (for 'balance') comes off. It kinda looks like there's a 'sleeve' with a pin thru it on the post that might come off, but can't figure out how.

Any tips?
 
The knobs do keep the dial glass in place but if you remove the chassis mounting screws (that are vertically oriented and come from below it), you might be able to gently back the chassis out of the console with glass as is.

I like to remove the glass while working on the radio just to keep it safe but there are certain things you can do with the glass in place, but the chassis out. Among them is deOxing the volume and tone controls.

Other things that typically get done while the chassis is out:
DeOxing the contacts of the function keys as well as the pivot points of the switch mechanism
Lubing the bearing of the tuning shaft
Cleaning with alcohol the dial string /wire including where it wraps around the tuning shaft
DeOxing the tube pins and the tube sockets

Electronics.......not for the faint of heart but here is what it will need, if not now, then for longevity:
Rectifier changed from selenium to a silicon full bridge rectifier with 100 ohm dropping resistor following the DC output
New filter caps - usually two 50uF or 100uF caps, 450V
New coupling caps to the power tube grids. Ideally you would replace all of the paper "Eros" caps that you can get to, but if you only do two of them, these are the ones to replace
New cathode bypass capacitors for the power tubes.

All of the above is very doable if you take your time and ask questions if you are stumped. We can help you. The underbelly can look pretty daunting. I broke my first Grundig at age 11 and have been treating them with a little more care in the 50 years that have followed, with good results. It can be a very rewarding thing to listen to a piece that you have brought back to life!
 
The knobs do keep the dial glass in place but if you remove the chassis mounting screws (that are vertically oriented and come from below it), you might be able to gently back the chassis out of the console with glass as is.

Ah ha, thank you! I assumed you'd need to take the knobs completely off to remove the unit. I see you can just disconnect and slide it out. Step one complete!

And yeah, I get the impression these grundigs are daunting to work on. I will most certainly be asking for some help as I move thru it, but maybe I'll just make it a winter long project. I'll post other specific forum posts here when I move onto part swapping. For now I'm going to get it pulled out, clean it, and see where I'm at.

Thanks for your willingness to help!!!
 
Old changers like this one are usually afllicted by the same disease - simply the rubber parts dry up and harden, and the grease congeals and becomes more like a glue.

The solution is a bit painful but is obvious. Take it apart, flush out all the old grease, and lubricate is carefully with new grease and oil. The rubber parts need to be replaced. Typically this means a rebuilt idler wheel and new motor mounts.

The controls can be cleaned, I suggest Caig deoxit on the switches, and faderlube on the controls. Test the tubes, and change paper and electrolytic capacitors.

I suggest to buy a small table radio, and restore it first, so you can cut your teeth on something simple. The grundig is complex, it's better to learn basic repair skills on an old chevy before attempting to fix a vintage Mercedes. Lots of forums can help. This one, and antiqueradios.com are both great sources of advice.
 
Old changers like this one are usually afllicted by the same disease - simply the rubber parts dry up and harden, and the grease congeals and becomes more like a glue.

At this point, my aim is going to be to clean it as best I can and see what that does for me. I'm certain there's other work that needs to be done (a constant hum tells me caps need replacing), but I'll think about that part later once the status is more clear after a cleaning.

Can I get a general guide on when to use which cleaners/lube products? When to use detoxit, when to use which lube, when to use alcohol etc? I want to be sure I don't use the wrong product on the wrong part and make the situation worse :)

PS: I'm fine at changing caps, which will get me down the road a little further..but wow...the bottom of this thing is daunting to look at!! Not sure I'll even be able to find what needs replacing!!
 
At this point, my aim is going to be to clean it as best I can and see what that does for me. I'm certain there's other work that needs to be done (a constant hum tells me caps need replacing), but I'll think about that part later once the status is more clear after a cleaning.

Can I get a general guide on when to use which cleaners/lube products? When to use detoxit, when to use which lube, when to use alcohol etc? I want to be sure I don't use the wrong product on the wrong part and make the situation worse :)

PS: I'm fine at changing caps, which will get me down the road a little further..but wow...the bottom of this thing is daunting to look at!! Not sure I'll even be able to find what needs replacing!!

Sure

Changer

Alcohol - use 99% not 70% from pharmacy. Use it to clean out all the old grease in the changer. Anything that slides against each other is going to have old grease. Once you get into it, it's going to be very obvious where it is. May need some disassembly to get all of it. Also, use it to clean the surface of the idler wheel, and the inside of the platter rim from any rubber residue. Expect to use lots and lots of Q-tips. I like to set up a changer upside down on blocks, on my desk, and get comfortable - this isn't a quick job.

Grease. - replace all the grease you cleaned out with alcohol. Also, grease the platter bearing. I use white lithium grease from an auto parts store. Any light grease will work here. Wheel bearing grease will do in a pinch. Be very sparing in application, don't get it anywhere which needs friction to work, or anywhere that didn't have grease from factory. The change cycle gear especially needs to be greased well.

Oil - Motor bearings, and a drop on the platter bearing. Nowhere else. use pure oil, not 3 in one which contains wax. "electric motor oil" from home depot is ideal.

Rubber Renew - an excellent product from MG chemicals, can be used to restore idler wheels which are hard but in otherwise good shape. If it has a flat spot it's too far gone.

Radio

Deoxit - Selector switches of all sorts, and first cleaning of potentiometers. Spray them and then operate them repeatedly.

Faderlube - Potentiometers - Get the spray inside them through holes or opening above terminals. Some pots need to be taken apart to clean properly. Once it's saturated, work it back and forth lots of times. Repeat as necessary.

Oil - one small drop on the shaft of potentiometers. Let it soak into the plain bearing and then wipe off excess. Work it in by operating control.

Grease - sometimes switch mechanisms can benefit from a bit of grease - and I mean a little bit. Can use a toothpick to apply it. use your judgement here.

General cleaning - Compressed air and a paint brush first, then spray windex or similar onto a microfiber cloth, and just clean the chassis gently. If you have no compressor, can vacuum it but be careful. Be especially careful around coils and anything delicate.

Recap - replace coupling capacitors to output tubes, and electrolytic filter capacitors as a rule. Others depend on how much voltage is across capacitor. Don't do anything with small capacitors in FM or IF section or expect non-working radio.

Another note - on the changer, one thing you have to understand is how the velocity trip works. This part of the mechanism can easily malfunction, and it's better to study in detail how it's supposed to work, and then service it from a position of understanding, than to apply grease and then wonder why it isn't working. Shotgun repair approach can ruin changers fast.
 
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PERFECT post here, thanks maxhifi! Going to get going on this during the Christmas break and we'll see where we land.

Once I get past that...I have a hard time reading the schematic I have (first, I dont read them well to begin with due to my lack of knowledge, but also because it's really small/blurry writing). Am I best to just identify all the paper caps, try to read them, and make a list? Then, ask about any other caps I have questions about? Just looking ahead to building a cap list, which seems a little daunting.
 
The big trick with most German radios is they are assembled in layers. Half the stuff you need to change will be up close to the chassis, and often there are other parts between you and it. The large switch mechanism in the middle of the chassis eats a lot of room too. Patience and a delicate touch are necessary on these. Be extra carefu around the piano keys. They tend to have some fragile coils attached to them and breaking them will kill the tuner. Some have pot metal parts in the tuning mechanism that will make it mechanically inoperable too. Not all of the parts need to be changed in these, but some of the parts that don't need to be changed don't like heat, so if you bump them with a soldering iron they will die. The clear caps are on that list. They are usually polystyrene, which is reliable but heat sensitive.
 
Be extra carefu around the piano keys. They tend to have some fragile coils attached to them and breaking them will kill the tuner
When you say 'kill the tuner', will it go dead completely? I ask because one of the issues I'm having is really weak signal to the tuner (which I'm hoping improves with caps/cleaning)..but if what you say is a common problem, I'm wondering if they could be the culprit.
 
PERFECT post here, thanks maxhifi! Going to get going on this during the Christmas break and we'll see where we land.

Once I get past that...I have a hard time reading the schematic I have (first, I dont read them well to begin with due to my lack of knowledge, but also because it's really small/blurry writing). Am I best to just identify all the paper caps, try to read them, and make a list? Then, ask about any other caps I have questions about? Just looking ahead to building a cap list, which seems a little daunting.

Mouser, etc have almost too much choice. For a beginner I suggest to order caps from https://www.justradios.com/
Just get all 630V yellow axial capacitors, same values as the old paper ones. For the electrolytics, you need to get creative. I suggest also go axial, and mount them on a terminal strip. Be very careful about grounding in the same spot as the old cans, so you don't introduce hum.

Best to troubleshoot and fix problems before beginning recap. If radio is dead now, don't change any parts en masse until it works, unless something is obviously very bad, like say a coupling cap red-plating an output tube.

Oh I almost forgot - also use deoxit on tube sockets. Spray them, then work a tube in and out. May also need to tighten the sockets, can do with a tiny screwdriver (don't forget that some pins may have high voltage on them, so use a plastic handle screwdriver and bleed off filter caps first)
 
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The knobs do keep the dial glass in place but if you remove the chassis mounting screws (that are vertically oriented and come from below it), you might be able to gently back the chassis out of the console with glass as is.

I like to remove the glass while working on the radio just to keep it safe but there are certain things you can do with the glass in place, but the chassis out. Among them is deOxing the volume and tone controls.

Other things that typically get done while the chassis is out:
DeOxing the contacts of the function keys as well as the pivot points of the switch mechanism
Lubing the bearing of the tuning shaft
Cleaning with alcohol the dial string /wire including where it wraps around the tuning shaft
DeOxing the tube pins and the tube sockets

Electronics.......not for the faint of heart but here is what it will need, if not now, then for longevity:
Rectifier changed from selenium to a silicon full bridge rectifier with 100 ohm dropping resistor following the DC output
New filter caps - usually two 50uF or 100uF caps, 450V
New coupling caps to the power tube grids. Ideally you would replace all of the paper "Eros" caps that you can get to, but if you only do two of them, these are the ones to replace
New cathode bypass capacitors for the power tubes.

All of the above is very doable if you take your time and ask questions if you are stumped. We can help you. The underbelly can look pretty daunting. I broke my first Grundig at age 11 and have been treating them with a little more care in the 50 years that have followed, with good results. It can be a very rewarding thing to listen to a piece that you have brought back to life!

I know this is an old thread, but it's exactly what I'm working on also. I have been buying consoles for the last 2 years with plans to refurbish them. I have not really gotten far because I am completly clueless. This thread really helped me a lot. I am trying to get an SO 112 PX model ready for my daughter's house warming party in December. Everything functions, it just doesn't sound very good (I know that it's not ever gong to sound THAT great).

Using the info in this thead, I was able to get the chassis out. Now I'm looking at something that looks like it could have been used on a WWII airfraft carrier! I want to complete the basic things listed below from this thread:

deOxing the volume and tone controls
DeOxing the contacts of the function keys as well as the pivot points of the switch mechanism
Lubing the bearing of the tuning shaft
Cleaning with alcohol the dial string /wire including where it wraps around the tuning shaft
DeOxing the tube pins and the tube sockets (May also need to tighten the sockets, can do with a tiny screwdriver)

Are there any videos which might give me some basic instructions on how to do these things? I have the chasis out and I have deoxit. Just need to know what's next.

Also, I was trying to get the AM/SB tuning mechanism cleaned up because it was hanging. The string portion that wraps around the tuner shaft pullie was completely black. It just slipped when I turned the knob. I tried to clean it the best I could, but wasn't successful. So, I decided to take it off and clean it. Big mistake. I doubt I'll ever get it back on! It's not a big deal because my daughter will never use the radio, much less AM, but of course, I'd rather it be 100% working. Any advice on this? BTW - the FM tuning string works fine.

Thanks in advance for any help.
 
Thought I'd post some pics if it helps. Not the 2 newer looking blue pieces on the underside. I originally took this too a shop and mistakenly asked them to "get it working". I think they did the minimum to get it working. I really meant for them to recap it, and do the steps you guys mentioned. I should have been more specific.
 

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