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Old 21st May 2022, 2:28 pm   #1
moss999
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Default Grundig TK24 belts location

Hi all , I have been asked to take a look at a family members TK 24 which is not playing , I have got the top cover off and found the remains of a couple belts , a 3mm diameter one which seems obvious where that one locates and a smaller around 1.5 mm diameter , this one I cannot see where it went .
Is there any "how to" links or any advice would be appreciated , also I wanted to take the bottom cover off to get at the caps etc , I see 4 screws in the feet but none of these seem to unscrew they just turn ? ..
Thanks .
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Old 21st May 2022, 10:21 pm   #2
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Default Re: Grundig TK24 belts location

Hello and welcome to the Forum.

There are 3 drive belts on the TK 24.

1. Flywheel to motor coupling 112 x 3
2. Flywheel to take up reel table 90 x 2
3. Supply reel table to tape counter 80 x 1.5

All the belt dimensions are nominal mm, ID x thickness/CSA

Normally the bottom cover screws just fully unscrew and are easily removable, do not think there is anything different with the TK 24, will double check my one tomorrow.

David
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Old 22nd May 2022, 11:09 am   #3
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Default Re: Grundig TK24 belts location

Thanks for the reply David. I have seen a belt set on eBay, I will get a set ordered.
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Old 22nd May 2022, 11:17 am   #4
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Default Re: Grundig TK24 belts location

Correction to above, unlike some other TKs the bottom cover of the TK 24 is not removable with the chassis in position.

To work on the underside of the chassis you have to remove the complete chassis from the case by removing the top fixing nuts and lifting out the chassis from the top. Also have to disconnect the loudspeaker wires and pull mains cable out to enable the chassis to be lifted out.

With the chassis out you can access the nuts that secure the feet securing screws which then may enable the bottom cover to be removed but there is no need to remove the bottom cover.

David
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Old 22nd May 2022, 6:16 pm   #5
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Default Re: Grundig TK24 belts location

Photo showing the belts.

David
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Old 23rd May 2022, 9:27 am   #6
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Default Re: Grundig TK24 belts location

Quote:
Originally Posted by DMcMahon View Post
. Also have to disconnect the loudspeaker wires.

David
By unsoldering from 2 way terminal posts.

David
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Old 23rd May 2022, 5:06 pm   #7
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Default Re: Grundig TK24 belts location

Opening the mains cable stowage compartment door on my TK 24 this beastie tumbled out.

Even though it was dead it really made me jump.

David
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Old 19th Jun 2022, 1:34 pm   #8
moss999
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Default Re: Grundig TK24 belts location

Quote:
Originally Posted by DMcMahon View Post
Opening the mains cable stowage compartment door on my TK 24 this beastie tumbled out.

Even though it was dead it really made me jump.

David
WOW !! that is a beast ,,
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Old 19th Jun 2022, 1:41 pm   #9
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Default Re: Grundig TK24 belts location

I have finally got some time to have a look at this ,am I correct in thinking to get at the belts I need to remove these 3 screws (see pic) and the whole plate lifts off , anything to be wary of ?
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Old 21st Jun 2022, 10:16 pm   #10
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Default Re: Grundig TK24 belts location

Apologies for slow response, I have only just seen the update.

Yes you have to remove those 3 screws and lift up the head assembly plate enough to be able to get the drive belts over the top of the upper capstan shaft and then onto the flywheel, the lower (smaller diameter part of the flywheel) is the belt to the take up spool table.

Assuming you have not done it already there are a few things to watch out for:-

There is a taut control wire on the right hand side going to the 3 input switch selection assembly. If you decide to remove the flywheel for cleaning and relubrication the lower capstan shaft bearing assembly (if this is done, watch out for ball bearing at bottom end of capstan shaft) the wire has to be disconnected by removing the wire ferrule from the switch assembly. This is impossible in the Stop position of the selector switch, you have switch the selector switch to another position which makes the wire a little less taut, then you move the little arm that the ferrule fits into, a few mm to the left by pushing over with finger, this gives more slack on the wire and makes it easy to remove the wire/ferrule.

When the heads assembly plate is lifted up it can be quite tight due the heads connecting wires and the EOT sensor wire (End Of Tape), the head wires are a little delicate so treat it with care.

You have to remove one end of the tension spring for the Pinch Roller Actuating Arm Assembly. At this stage with heads assembly lifted it is a good opportunity to clean and relubricate the selector switch assembly and its cams.

Also seen in your photo is the coiled spring arm that connects to the Supply spool actuating arm and connects across horizontally (via a link arm) to the Take Up spool actuating arm. When lifting up the heads assembly it is quite easy to disturb (may come disconnected) the spring so note first its connection positions.

Before disturbing anything take photos of relevant parts and take note of how it all works mechanically. It is a little fiddly but all doable.

The tape counter belt of course can easily be replaced at any time.

David

Last edited by DMcMahon; 21st Jun 2022 at 10:22 pm.
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Old 22nd Jun 2022, 10:07 am   #11
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Default Re: Grundig TK24 belts location

Better photo than Post 5, showing the 2 main drive belts.

David
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Old 22nd Jun 2022, 6:17 pm   #12
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Default Re: Grundig TK24 belts location

Thanks for that info , I had already taken a chance and got them fitted , fiddly not an understatement .. belts all seem to be doing their job ok although I seem to have a very noisy volume pot and very low volume at all positions ,,

I read on another post the dull side of the tape touches the head so that is correct , can the volume pot be cleaned as any other with contact cleaner and working it many times ?
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Old 23rd Jun 2022, 2:58 pm   #13
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Default Re: Grundig TK24 belts location

Good progress.

Yes a spray of contact cleaner into the pot body near contacts/wiper end (normally a small hole/gap somewhere) will normally fix noise/crackling, may not fix low volume though.

David
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Old 9th Jul 2022, 1:30 pm   #14
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Default Re: Grundig TK24 belts location

Hi , I cleaned the volume pot , much better though but as you said , did not help with the low volume , I read in another post you said to lightly touch the head wires and should hear a hum which I did not .
I measured some voltages around the tubes which I think are the audio , I am used to tinkering with modern stuff but this old school stuff is all new to me ,,,
See photo for voltages I measured all other pins are 0 volts ,

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That capacitor is looking a bit funky too
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Old 9th Jul 2022, 1:36 pm   #15
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Default Re: Grundig TK24 belts location

Hi , I cleaned the volume pot , much better though but as you said , did not help with the low volume , I read in another post you said to lightly touch the head wires and should hear a hum which I did not .
I measured some voltages around the tubes which I think are the audio , I am used to tinkering with modern stuff but this old school stuff is all new to me ,,,
See photo for voltages I measured all other pins are 0 volts ,

Attachment 260644
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Old 9th Jul 2022, 1:37 pm   #16
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Default Re: Grundig TK24 belts location

That capacitor is looking a bit funky too !
Also a link for higher res photo

https://www.dropbox.com/s/54i6t6mrdzh2wbm/tk24.JPG?dl=0
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Old 9th Jul 2022, 10:33 pm   #17
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Default Re: Grundig TK24 belts location

Yes the first 2 audio valves, the EF 86 and the ECC 81.

From your photo cannot easily see what pins equate to each voltage reading, can you identify the pin numbers. From voltage values shown on the schematic some of your readings may be suspicious.

It also would be worthwhile getting the voltage readings from the EL 95 output valve , the valve under those two in bottom corner by the output transformer.

The funky capacitor (I assume you mean the crazed one) and the 0.022uF next to it are the somewhat infamous brown/black Wima paper capacitors (commonly called "Toffee sweets") which have quite a bad reputation for going electrically leaky when old.

These type of capacitors often need to be replaced.

Are the valve heaters/filaments lighting up ?

Is the EM 84 Magic Eye valve illuminating with its green display ?

David

Last edited by Cobaltblue; 18th Jul 2022 at 9:18 am. Reason: corrected "Toffee sweets" as per OP post
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Old 23rd Jul 2022, 3:42 pm   #18
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Default Re: Grundig TK24 belts location

Sorry for the delay in replies , I don't seem to get much spare time lately . yes crazed , much better description , all the valves I can see are lit up as is the green eye tube , Here is a pic to clarify the voltage readings ..

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Old 23rd Jul 2022, 7:40 pm   #19
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Default Re: Grundig TK24 belts location

First small thing is that 2 of your valves are incorrectly identified on your drawing.

The "BC81" should read "ECC 81" and "BC86" should read "EF 86".

Comparing your voltage results with the schematic there are several that are not correct and need further investigation.

First I would strongly recommend you check out your DC +HT supplies, namely main +HT at reservoir capacitor C31 (shown as 255V), +HT1 at filter/smoothing capacitor C21 (shown as 240V), +HT2 at filter/smoothing Capacitor C19 (shown as 230V) and +HT3 at filter/smoothing Capacitor C15 (shown as 190V).

All the DC HT voltages are positive and the meter negative lead should be connected to ground/0V/chassis/earth.

Due to ageing components your HT voltages will probably be somewhat lower than the values shown on the schematic but they should be somewhere reasonably close. If any abnormally low then would suspect the associated capacitors (or less likely extreme load somewhere pulling the voltages down). If all the HT voltages are very low then also could suspect the metal bridge rectifier.

ECC 81 - The first anode voltage on pin 6 of 15V is very low, 140V shown on schematic, would initially suspect the anode dropper/load resistor R26 (200k) has gone very high or the +HT2 voltage of 230V (at top end of R26) is very low.

Note - pin 1 of the valves is the first pin on the left when viewing the valve base from its underside.

EF 86 - The anode voltage on pin 6 is well low at 56V, schematic shows 150V, would initially suspect anode dropper/load resistor R21 (200k) has gone high resistance or the +HT3 voltage of 190V is low.

EF 86 - The G2 grid voltage on pin 1 of 12.5V is somewhat low, schematic shows 42V. Could be high resistance R22, G2 decoupler C16 being leaky (very possible if a Wima Toffee sweet) or low +HT3.

ECC 81 - The G1 grid voltage on pin 7 of 3.6V should be closer to 0V, not sure at the moment if pin 7 is first stage G1 or the second stage, if first stage then the voltage may change/increase as the volume control is adjusted, then would suspect leaky C17 and C18, if second stage then would suspect leaky C20.

EL 95 - Your voltages appear to be totally wrong (wrong pins ?) I need to study it more to better understand.

David

Last edited by DMcMahon; 23rd Jul 2022 at 8:03 pm. Reason: Update
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Old 23rd Jul 2022, 8:10 pm   #20
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Default Re: Grundig TK24 belts location

I assume that your valve base drawing in Post 18 is the underside view of the valve bases.

David
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