Oiling a Grundig TK20 and capacitor choices

[DMcMahon]

Note that some of the modern all singing all dancing component test meters may give higher capacitance reading result if the capacitor ESR is high, i.e. higher than the capacitance actually is, an analogue bridge type instrument will be less effected by the high ESR and give a more accurate capacitance reading.

If the fitted motor capacitor is in good physical condition and measures OK then it may well last for a lot longer.

David

[DMcMahon]

For general oil lubrication I use Singer Super Oil, which is a good quality light oil for sewing machines.

Was not aware of the Singer grease, will get some of that to try out.

David

[JonSnell]

THe motor run capacitor need not be exact in capacitance value. It plays no part in the motor speed just points the motor in the right direction, by introducing phase shift. If too low a value the motor will lose torque, too high and it may run hot.

[JonSnell]

Originally Posted by DMcMahon

For general oil lubrication I use Singer Super Oil, which is a good quality light oil for sewing machines.

Was not aware of the Singer grease, will get some of that to try out.

David

I am sure I have never replaced the motor capacitor on any Grundig. I ran a large Grundig Regional Service Centre for many years, supplying parts and replacement panels when Willow Vale stopped. I had one in stock that I still have somewhere.
If you use oil on a motor bearing, the oil will leech out of the bearing, spraying a fine mist that may attract dust. Eventhough it is cintered, not sure why they stiil call them 'Oilite Bearings'. Perhaps they don't.
Most Singer sewing machine service manuals state that point.
Hope that helps.

[JohnM73]

Interesting to learn all this. My TK20 is in very good condition (I’m pretty sure it was barely used in fact) so keen to take my time and use the right parts and lubricants etc. Have used Mobil DTE Medium for the main motor, just a few added drops, and it’s spinning very freely indeed. I’ll go for the Singer grease for the capstan/flywheel, assuming the picture I posted on the previous page is the correct item? I also spotted this that might also be suitable:

https://www.the-littlest-thistle.com...ewing-machines

[JohnM73]

Originally Posted by JonSnell

THe motor run capacitor need not be exact in capacitance value. It plays no part in the motor speed just points the motor in the right direction, by introducing phase shift. If too low a value the motor will lose torque, too high and it may run hot.

So given the choice between 1uF and 1,5uF, is 1 likely to be the safer bet? Sorry for the ‘newbie’ type questions.

[JohnM73]

Just measured the caps again out of circuit, and the two 16uF/350V caps are 19.45 and 19.13uF, so will go for the 22uf 450V PEG124 types. The original 40uF measures 47uF, so will go for that value. Should get me into the correct ballpark in each case.

The motor run cap measures 1.32uF, so will probably go for the 1uF Kemet C87 type with a suitable 200nF cap to get it to around the specified 1.2uF. Would the trim cap need to be a motor run type too? I guess as this deck was barely used I might be able to get away with running the original motor run cap still, but as I'm in there I might as well refresh those too just to be thorough and 'future proof' it a little further.

Word is the modern Singer Lubricant is not as good, so will likely go for the one linked a couple posts above, for the capstan/flywheel lubricant.

[JohnM73]

“Word is the modern Singer Lubricant is not as good as their older formulation”, that should have said. Whether this is true or not I don’t know, but (and yes, likely going into this in WAY to much detail now!) read the following:

https://archaicarcane.com/a-search-f...e-replacement/

[JonSnell]

If you think you will need the extra torque, a 220nF Class X or Y 250v AC capacitor will be best. If they fail, they fail open circuit.
Belt and braces.

I must agree, Vaseline will do nicely.

[JohnM73]

Originally Posted by JonSnell

If you think you will need the extra torque, a 220nF Class X or Y 250v AC capacitor will be best. If they fail, they fail open circuit.
Belt and braces.

I must agree, Vaseline will do nicely.

Cheers for confirming that, have now gone and ordered all remaining caps needed (already got Panasonic polyester replacements for those pesky 'toffee' WIMAs). Hopefully I'll be able to get stuck into it again in the coming week, energy permitting.

One question you might know the answer too, I'm usually very good at taking more than enough photos so that I can usually get myself out of any 'now where does that go again' scrapes. But there's one cap which I'm unsure about and my photo is obscuring the leg on the side in question. It's labelled EROID, type K1084, and is 0,01uF, 250V. I think it's C13, a film cap filled with a clear amber potting. Looking at the removed cap, it appears to have the remnants of a third leg (!). Wondering if it had a shielding connecting outer layer to earth for some reason... Does this ring any bells at all? If not I have a spare TK20 somewhere in Loftsville so will have to take that apart and check. Checking the circuit diagram it seems to suggest something about an outer coating, so perhaps shielding?

[JonSnell]

Originally Posted by JohnM73

Cheers for confirming that, have now gone and ordered all remaining caps needed (already got Panasonic polyester replacements for those pesky 'toffee' WIMAs). Hopefully I'll be able to get stuck into it again in the coming week, energy permitting.

One question you might know the answer too, I'm usually very good at taking more than enough photos so that I can usually get myself out of any 'now where does that go again' scrapes. But there's one cap which I'm unsure about and my photo is obscuring the leg on the side in question. It's labelled EROID, type K1084, and is 0,01uF, 250V. I think it's C13, a film cap filled with a clear amber potting. Looking at the removed cap, it appears to have the remnants of a third leg (!). Wondering if it had a shielding connecting outer layer to earth for some reason... Does this ring any bells at all? If not I have a spare TK20 somewhere in Loftsville so will have to take that apart and check. Checking the circuit diagram it seems to suggest something about an outer coating, so perhaps shielding?

Quite possibly b ut a standard 10nF poly cap should suffice I would think.
Some did have a screen around them connected sometimes to ground. That was to reduce RF interference from the bias oscillator etc but in this case I would think it is the foil coming away perhaps.

[JohnM73]

Have just been looking at pics from a TK28 restoration, and saw the picture below, so it seems it is one of those same caps with shielding. Looking at the removed cap in front of me, there's very definitely remnants of the end of a third wire there too on the outer winding. Was very stupid of me not to take a picture closer in to see exactly what went where. Do you think with a replacement it might be an idea to wrap copper tape around it once, and get a wire in there to replicate the shielding? I noticed on my TK20 there is a nub of wire there where black wires meet, so must be an earth point.

[DMcMahon]

Have often seen the outer screening foil indication symbol on the Grundig (and maybe others) schematics, but normally when I have previously replaced said capacitors they are standard 2 leg capacitors. I wonder if this is a German trait because UK Grundig schematics often do not show the outer foil symbol.

Checking my first TK 20, it has the same 3 leg C13 as yours.

The screening foil connection leg is the one on the bottom left of the photo, the leg is on the outside edge of the capacitor as opposed to the normal 2 legs which are centralised.

The foil leg connects to the first terminal of the terminal strip where a black wire also connects up to earth/metalwork connection at valve base. The screen of the screened cable (that connects to the input of C13) also connects to the left hand terminal of the terminal strip.

My C13 measures 27nF & 22 Ohms ESR, so I will replace it with a standard Polypropylene, there is no direct connection to DC voltage so it may well be OK but as it is one of the easiest to replace might as well replace.

David

[JohnM73]

Thanks for taking the trouble to take a look on your TK20 David, that’s great to have that confirmed, and exact location of the shielding wire. I’m wondering how to replace it - would a standard 0,01 cap, with copper foil wrapped around it and a wire (somehow) attached be worth doing? Grundig evidently made the effort to fit a shielded cap here, for whatever reason, and I assume I should replicate that somehow.

[DMcMahon]

Capacitor technology has improved dramatically since these were fitted over 60 years ago.

I would just try a standard capacitor, I very much doubt there will be an issue.

Sometimes online the 3 legged foil capacitors are sold as well as very expensive audio grade capacitors, some of which may extend into Audiophoolery.

David

[emeritus]

The lubricants specified in the official service manual for my 1970's Philips cassette recorder are ordinary 20W50 engine oil and ordinary automotive lithium bearing grease. Ordinary grease consists of a mixture of oil and a soap which makes the oil stay put. Hardened grease is just the soap that is left behind after the oil has evaporated.

[DMcMahon]

Originally Posted by DMcMahon

My C13 measures 27nF & 22 Ohms ESR, so I will replace it with a standard Polypropylene, there is no direct connection to DC voltage so it may well be OK but as it is one of the easiest to replace might as well replace.

David

As an interesting test I will leave my original C13 in place until I get the unit up and running and then replace it to see if any detectable difference, I very much doubt there will be any difference in performance either by listening tests or measurements.

David

[JohnM73]

Originally Posted by DMcMahon

As an interesting test I will leave my original C13 in place until I get the unit up and running and then replace it to see if any detectable difference, I very much doubt there will be any difference in performance either by listening tests or measurements.

David

That’ll be interesting to see if there’s any difference at all. I’m really just replacing it as I’ve noticed from photos on other decks that these can crack from heat/old age and the capacitance can then alter, so as the deck is being given a full recap I thought I’d replace it too. I’ve ordered a Vishay 1813 type polyester to replace it with, just to keep close to the original look/size. I think just to keep as close to stock as possible, I will solder a wire to some copper tape, then wrap a single layer around the cap, and finish it off with some clear heatshrink so it doesn’t short to anything. As you say though, highly likely that shielding offers little to no difference especially with a modern cap.

[JohnM73]

Originally Posted by emeritus

The lubricants specified in the official service manual for my 1970's Philips cassette recorder are ordinary 20W50 engine oil and ordinary automotive lithium bearing grease. Ordinary grease consists of a mixture of oil and a soap which makes the oil stay put. Hardened grease is just the soap that is left behind after the oil has evaporated.

Thanks for that - always good to know what was originally used back when. I’ve used a few drops of Mobil DTE Medium for the main motor, and (following the discussions here) will simply be using a little Petrolium Jelly to lube the capstan/flywheel bearing and shaft once cleaned of the old hardened lubricant.

[emeritus]

Although petroleum jelly (Vaseline) superficially resembles lubricating grease, its mechanical properties are very different. You would never dream of putting ordinary grease on the contacts of plug and sockets or switches: grease would affect the contact resistance as it is designed to stay put under pressure and prevent adjacent surfaces from coming into physical contact. On the other hand, the Vaseline that is applied to the lugs, including the mating surfaces, of car batteries to protect them from corrosion, does not affect the contact resistance at all because it readily flows under pressure, allowing the adjacent surfaces to come into intimate contact. It is therefore unlikely to provide effective long-term lubrication.