Grundig TK20

[GerryE582]

Hi,

I have recently purchased a Grundig TK20 to allow me to play some old family reel to reel tapes. The player I purchased had no drive belts with it so I purchased a set of 3 from eBay and would like to fit them. Having looked I cannot be sure of the correct locations for the belts and am hoping someone on here may be able to advise how to go about replacing these.

Regards

Gerry

[DMcMahon]

Hello Gerry and welcome to the Forum.

The attachments should help somewhat. Once you have done it once it is fairly straight forward compared to some recorders.

The small thin tape counter belt is very simple.

The other 2 thicker belts both go around the capstan flywheel, the top wider section of the flywheel belt goes to the motor pulley, the lower smaller diametert section of the flywheel goes to the RHS Take Up Spool Table, you can see this belt at lower groove in clutch section in attachment 2.

To fit the 2 belts to the flywheel you first have to remove the securing screws of the head plate that the heads etc sit on, then lift the plate up enough so that clears the top of the capstan shaft and gently rest it down out of the way, watching out not to stress the head cabling.

If I remember correctly you first have to disconnect the Pinch Wheel lever arm assembly to get it away from the head plate.

You may be able to push the belts down between the tight gaps for the idler and the motor pulley, if not you just take apart the top section of each spool table.

Before you disturb anything take photos of how it is now and take many photos/notes whenever you remove/disturb anything.

One thing to watch out for is the capstan flywheel vertical movement/play. Before you do anything grab hold of the capstan shaft and pull it up until it will not lift any higher, it will be a few mm max. Note the amount of movement. When re-assembled recheck the amount of movement, it should be the same. If it has increased by 2 or 3mm then that would mean that the ball bearing that sits inside the lower bearing assembly at the base of the capstan shaft has come adrift.

The ballbearing is normally stuck to the bottom of the shaft by grease but due to age the grease may well have turned to dust, so try not to lift the flywheel up too much when fitting the belts.

David

[ben]

Weren't there a couple of wax caps in this model that always go leaky?

[DMcMahon]

Not as far as I know. From my experience the only waxy (wax covered) capacitors in the TK 20 and similar late 1950's Grundig R2Rs are a few waxy silvered mica which as you know are generally very reliable.

However the numerous coupling/decoupling etc capacitors in these machines are typcically paper (di-electric) such as the brown/black Wima (commonly called Toffee/Lozence sweets because of their shape) and these often will have become electrically leaky. Not so common in these machines but there can also be Hunts Moldseals and similar ones by ERO/EROS etc., which can also go leaky.

Gerry, Ben raises an important point about capacitor reliability, this can also lead onto the thorny subject of "recapping".

Do you have any electrical/electronic experierence, do you have any test equipment such a DMM to measure DC voltage, are you confident/competant to work inside the machine when it is live to measure voltages ?

Apart from general reliability concerns there is one fairly major concern with one coupling capacitor that couples the audio signal to the output valve to drive the loudspeaker via the output transformer. If the capacitor has gone very electrically leaky it can cause the output valve to overdrive, potentially worst case damaging the valve and output transformer. Not a common event but can occur.

Have you already powered the recorder up ?

David

[DMcMahon]

Checking the TK20 schematic there are 2 capacitors connected in series coupling the anode (pin 1) output of the ECC81 valve to the control grid (pin 1 & 7) input of the EL95 Pentode output vave.

Namely C22 (0.1uF) and C26 (0.047uF), so this is good as it reduces the risk of +ve DC voltage getting through to the EL95 valve input.

David

[GerryE582]

Thanks David and Ben for getting back to me. I have powered up the machine and all appears to work but until I have the belts on that is not guaranteed to be correct. I will put the belts on and let you know how that goes and fingers crossed the speaker etc will work. As I said this is to see if there is anything of note on some old family tapes - if there is then I will need to dig deeper to repair it properly.

Again many thanks for your help so far.

Gerry

[DMcMahon]

After you fit the belts, leave the top panel off before you power up and watch out for any whisps of smoke and check for any overherating smells (watch out for live voltages on the EM84 Magic Eye valve base).

David

[ben]

Test with a junk tape, not one of your home recordings, for all you know the thing could erase whatever you play on it. Ebay or the wanteds on here might provide one if you don't have one.

[GerryE582]

Hi Folks,
Thanks for all the responses so far.
It has been a while before I could get back to the drive belts. I fitted them yesterday as per the diagrams and they appear to work correctly however when the machine is set to play it will go for about 2-3 minutes before it slows down and stops - moving to any other position FF or rev for example have no effect. If I then turn it off and back on I can repeat the same process. Also there was no sound at all coming from the onboard speaker.
As my electronics knowledge is very little is this a task too much for me?
Regards
Gerry

[Edward Huggins]

This all suggests a lack of torque within the drive mech and playback issues. If you feel you may need help, there are Members in your area and you can post a request in the "Help Needed" section on this Site.

[DMcMahon]

With the volume turned upto maximum there should at least be a little hum heard and some hiss (if tape loaded) during playback.

If no sound at all then make sure the loudspeaker is not switched off, i.e. the tone/record level control is not pulled up, push it down to make sure the loudspeaker is switched in. The difference between the down position and the up position is very small.

David

[DMcMahon]

Originally Posted by GerryE582

when the machine is set to play it will go for about 2-3 minutes before it slows down and stops - moving to any other position FF or rev for example have no effect. If I then turn it off and back on I can repeat the same process.
Regards
Gerry

What happens to the motor/motor pulley. With the machine powered up the motor pulley will rotate all the time at bascially the same speed both for play and fast wind. Likewise the flywheel/capstan shaft should rotate all the time as long as its drive belt is not slipping.

David