Grundig TK120 tape recorder - UK Vintage Radio Repair and Restoration Discussion Forum

SteveCG · 24th Jul 2019, 11:48 am

I've just acquired this late 1960s, 1/2 track mono, valve tape recorder.

I've got service info on it and shall examine it shortly - yes, be careful not to unscrew the 4 sealed fastenings!

My question is simply this: Is this a model where I'll have to change paper capacitors?

Welsh Anorak · 24th Jul 2019, 1:04 pm

I'd say not - they used a simple two-valve circuit with pretty good capacitors. There's an odd low-value fuse on the back panel (80mA?) that blows for no obvious reason and can fool you. Low sound and a hum is due to a 150k resistor in the first preamplifier stage.
Other than the belt cracking and the odd little wheel on the function switch detent (yours is an early version so should be OK - if not an old pinchroller and some ingenuity will do) there's not much mechanical to worry you. Sometimes the motor can be a bit reluctant to spin, but a bit of persuasion does the trick.
My first tape recorder when I was very young was a TK124 and was miles better than the Ferguson I replaced it with. That's the posh version with the proper level meter and lots of Sixties chrome!

SteveCG · 24th Jul 2019, 2:20 pm

Thanks for that Glyn. The first tape recorder I was able to use was my father's - a Grundig TK35. It seemed to get through drive belts, but it introduced me to 'magic eye' level indicators - rather like that of this TK120.

SteveCG · 25th Jul 2019, 12:30 pm

An update:

I've removed the top and bottom covers. The belts are all intact. The 'paper' capacitors are WIMA brand with the exception of a replacement grey RS one which is not mounted very well at all - for no apparent reason; I'll replace it.

Apart from some rust - and a rather clagged up capstan, it looks hopeful. My next goal is to work out what function that RS capacitor has and then to clean the tape recorder up sufficiently to see if the head is intact by playing a tape.

This will be another tape recorder I've met from the mid to late 60s where the belts are still intact - unlike those from the 70s where goo is the name of the game.

I tried it very, very briefly when I first got it and whilst the spool holders turned (I could not see the capstan - it is rather buried in the head cover design) there was a sound rather like a concrete mixer, so I'm expecting to find that the bottom capstan bearing needs greasing. My only concern is whether this is a 'critical alignment' situation.

SteveCG · 26th Jul 2019, 11:01 am

A further update:

Finally got the pcb swung out. A 0.01uF, 400V Wkg WIMA capacitor shown on the circuit diagram connects the anode of the first half of the ECC83 to the grid of the second half of the ECC83. It had been replaced with a 0.01 uF, 600V RS one.

Also I found that the bias oscillator coil was hanging just by its leads. I pushed it back into its mounting hole on the pcb and have applied some UHU glue to lock it in place.

Welsh Anorak · 26th Jul 2019, 1:54 pm

Bear in mind that the machine does sound like a concrete mixer if it's not horizontal. It's OK to remove the lower bearing to grease it. WIMA capacitors do fail as you have found, and it might be a idea to do some checking and replacing. Also the RS capacitor would probably be in need of replacement, even if it was the correct value!

SteveCG · 26th Jul 2019, 2:17 pm

Glyn, the machine was horizontal... The concrete mixer analogy I was thinking of is when there is a brick in it to clean it out... Clump ….. clump, etc.

As for the capacitors - yes, I'm replacing that RS one and will be checking the voltages on the valve pins - I have the 1968/69 Radio and TV Servicing book info. I'm intending to check the RS and its replacement for leakage with about 400V applied in series with an analogue voltmeter.

Top Cap · 26th Jul 2019, 5:14 pm

For £1.99 it is worth getting the Trader sheet as available at top of page..
https://www.service-data.com/product...80/3461/e12580
Not only a much clearer circuit diagram but setting up of deck mechanics and electrical test procedures too.

SteveCG · 27th Jul 2019, 10:07 am

Thanks for the advice Top_Cap, however I already have the full service manual - but in German. I agree though that it gives more detail than the RTVS entry.

For interest, the RS 0.01 uF, 600 V Wkg capacitor had a leak current of about 0.5 uA with 320 Volts across it. I replaced with a 630 Volt non-paper one which was to hand whose leakage current was unmeasurable to me at 320 Volts.

The lower capstan bearing has been re-greased - even though I reckon there was still grease present.

Next steps are to reassemble, finish cleaning the capstan - it still has gunk on it, and then after a demagnetization, switch on bringing the mains voltage up slowly using a variac.

A question about the pressure pad - should it have some foam rubber behind the surface that is in contact with the tape?

SteveCG · 29th Jul 2019, 10:20 am

Right,
The tape recorder plays back. I've not attempted 'record' yet. A brief check of the HT voltages puts them about right - but I shall check in more detail.

Progress.

Uncle Bulgaria · 29th Jul 2019, 10:27 am

If you're on the lookout for the little fuses, I get 80mA 250V slow-blow types from RS.

SteveCG · 29th Jul 2019, 10:30 am

Uncle_Bulgaria - thanks for the fuse source advice.

SteveCG · 2nd Aug 2019, 12:01 pm

Tried recording using a 5 3/4 inch spool of Standard Play EMI tape. That worked and it erased the previous recording. The bias oscillator frequency was 58.3 kc/s - I only had to hold my meter probe near the wires to the heads to get a reliable signal !

The only issue I have is that its rewind is lacking in power, probably due to the small rubber tyre on the motor spindle being shiny - I don't think it is a 'sticky-shed' issue. Fast forward is fine. A clean with IPA - or will I have to roughen the surface of the tyre?

Tractorfan · 6th Aug 2019, 12:44 pm

Hi,
Dad bought a TK120 back in 1967. And it has given us many years of fun and memories. I have now 'inherited' it, and it still works well. I only had to replace the EM84 and the ECL86 many years ago. I think it's even still on its original belt!
The rewind always was mediocre at best, and it was down to the rubber wheel having insufficient traction against the L.H. plastic turntable. I used to ease the spindle slightly to the right with my finger nail to improve matters.
More recently, I found a flat rubber belt (I know not from where) that fitted snugly around said turntable. The rewind function is now much more brisk!
Cheers, Pete.

SteveCG · 6th Aug 2019, 12:54 pm

Pete, a thin flat rubber band eh - what good, lateral thinking! I'll look out for one.

SteveCG · 16th Aug 2019, 11:21 am

Pete (Tractorfan),

I came across some discarded rubber bands - 'standard issue' Royal Mail I believe. These are nearly the right dimensions, so I tried out your suggestion.

The rewind was certainly a lot better, however the tension of the band on the reel holder was not quite enough to hold it on for long. So as part of experimentation I'm thinking that I could cut out about 10% of the band and glue it together again. I have read on the forum of superglue being successfully used on drive belts, but since I have found that superglue containers once opened tend to ooze - no matter what you try doing to stop it - I am proposing trying UHU glue, which I already have.

Tractorfan · 18th Aug 2019, 9:27 am

Hi,
Glad my suggestion bore fruit for you.

I can't remember whether the band I fitted was snug enough to grip the turntable, or whether I used a bit of glue.
The rewind was sluggish, even from new, and it would be interesting to know if other machines of that range were the same.
Anyone?
Cheers, Pete.

SteveCG · 19th Aug 2019, 10:30 am

Yes, thanks Pete. I've yet to try the gluing experiment, its on the round-tuit pile. However I was thinking of using a Bib tape splicer, with its two pads, as a way of holding the band in place while the glue sets.

I'll update the results.

A question Pete: - does your machine use any foam rubber in the tape pressure pad? Mine does not, but I'm not sure that Grundig ever used it.

Tractorfan · 21st Aug 2019, 7:43 pm

Hi Steve,
Not foam rubber. I think it's a felt pad on a springy brass strip. I can't be 100% certain, but I'll whip the cover off and have a shufty next time I get a minute.
Cheers, Pete.

SteveCG · 22nd Aug 2019, 12:41 pm

Thanks Pete.

I tried the splicing experiment. It all worked nicely - except that UHU is just not strong enough. So I'll try superglue - when I have something else that needs it (read post no. 16 for why).

BTW: The Bib splicer is actually a cassette tape splicer and I used a cut-off section of the polythene wrapper from a Radio Times as an outer sandwich to keep the glue off the actual splicer.

24th Jul 2019, 11:48 am	#1
SteveCG Nonode Join Date: Jun 2009 Location: Herefordshire, UK. Posts: 2,495	Grundig TK120 tape recorder I've just acquired this late 1960s, 1/2 track mono, valve tape recorder. I've got service info on it and shall examine it shortly - yes, be careful not to unscrew the 4 sealed fastenings! My question is simply this: Is this a model where I'll have to change paper capacitors?

24th Jul 2019, 1:04 pm	#2
Welsh Anorak Dekatron Join Date: Apr 2005 Location: North Wales, UK. Posts: 6,916	Re: Grundig TK120 tape recorder I'd say not - they used a simple two-valve circuit with pretty good capacitors. There's an odd low-value fuse on the back panel (80mA?) that blows for no obvious reason and can fool you. Low sound and a hum is due to a 150k resistor in the first preamplifier stage. Other than the belt cracking and the odd little wheel on the function switch detent (yours is an early version so should be OK - if not an old pinchroller and some ingenuity will do) there's not much mechanical to worry you. Sometimes the motor can be a bit reluctant to spin, but a bit of persuasion does the trick. My first tape recorder when I was very young was a TK124 and was miles better than the Ferguson I replaced it with. That's the posh version with the proper level meter and lots of Sixties chrome! __________________ Glyn www.gdelectronics.wales

24th Jul 2019, 2:20 pm	#3
SteveCG Nonode Join Date: Jun 2009 Location: Herefordshire, UK. Posts: 2,495	Re: Grundig TK120 tape recorder Thanks for that Glyn. The first tape recorder I was able to use was my father's - a Grundig TK35. It seemed to get through drive belts, but it introduced me to 'magic eye' level indicators - rather like that of this TK120.

25th Jul 2019, 12:30 pm	#4
SteveCG Nonode Join Date: Jun 2009 Location: Herefordshire, UK. Posts: 2,495	Re: Grundig TK120 tape recorder An update: I've removed the top and bottom covers. The belts are all intact. The 'paper' capacitors are WIMA brand with the exception of a replacement grey RS one which is not mounted very well at all - for no apparent reason; I'll replace it. Apart from some rust - and a rather clagged up capstan, it looks hopeful. My next goal is to work out what function that RS capacitor has and then to clean the tape recorder up sufficiently to see if the head is intact by playing a tape. This will be another tape recorder I've met from the mid to late 60s where the belts are still intact - unlike those from the 70s where goo is the name of the game. I tried it very, very briefly when I first got it and whilst the spool holders turned (I could not see the capstan - it is rather buried in the head cover design) there was a sound rather like a concrete mixer, so I'm expecting to find that the bottom capstan bearing needs greasing. My only concern is whether this is a 'critical alignment' situation.

26th Jul 2019, 11:01 am	#5
SteveCG Nonode Join Date: Jun 2009 Location: Herefordshire, UK. Posts: 2,495	Re: Grundig TK120 tape recorder A further update: Finally got the pcb swung out. A 0.01uF, 400V Wkg WIMA capacitor shown on the circuit diagram connects the anode of the first half of the ECC83 to the grid of the second half of the ECC83. It had been replaced with a 0.01 uF, 600V RS one. Also I found that the bias oscillator coil was hanging just by its leads. I pushed it back into its mounting hole on the pcb and have applied some UHU glue to lock it in place.

26th Jul 2019, 1:54 pm	#6
Welsh Anorak Dekatron Join Date: Apr 2005 Location: North Wales, UK. Posts: 6,916	Re: Grundig TK120 tape recorder Bear in mind that the machine does sound like a concrete mixer if it's not horizontal. It's OK to remove the lower bearing to grease it. WIMA capacitors do fail as you have found, and it might be a idea to do some checking and replacing. Also the RS capacitor would probably be in need of replacement, even if it was the correct value! __________________ Glyn www.gdelectronics.wales

26th Jul 2019, 2:17 pm	#7
SteveCG Nonode Join Date: Jun 2009 Location: Herefordshire, UK. Posts: 2,495	Re: Grundig TK120 tape recorder Glyn, the machine was horizontal... The concrete mixer analogy I was thinking of is when there is a brick in it to clean it out... Clump ….. clump, etc. As for the capacitors - yes, I'm replacing that RS one and will be checking the voltages on the valve pins - I have the 1968/69 Radio and TV Servicing book info. I'm intending to check the RS and its replacement for leakage with about 400V applied in series with an analogue voltmeter.

26th Jul 2019, 5:14 pm	#8
Top Cap Octode Join Date: Mar 2006 Location: Watford, Hertfordshire, UK. Posts: 1,270	Re: Grundig TK120 tape recorder For £1.99 it is worth getting the Trader sheet as available at top of page.. https://www.service-data.com/product...80/3461/e12580 Not only a much clearer circuit diagram but setting up of deck mechanics and electrical test procedures too. __________________ Whether the Top Cap is Grid or Anode - touching it will give you a buzz either way!

27th Jul 2019, 10:07 am	#9
SteveCG Nonode Join Date: Jun 2009 Location: Herefordshire, UK. Posts: 2,495	Re: Grundig TK120 tape recorder Thanks for the advice Top_Cap, however I already have the full service manual - but in German. I agree though that it gives more detail than the RTVS entry. For interest, the RS 0.01 uF, 600 V Wkg capacitor had a leak current of about 0.5 uA with 320 Volts across it. I replaced with a 630 Volt non-paper one which was to hand whose leakage current was unmeasurable to me at 320 Volts. The lower capstan bearing has been re-greased - even though I reckon there was still grease present. Next steps are to reassemble, finish cleaning the capstan - it still has gunk on it, and then after a demagnetization, switch on bringing the mains voltage up slowly using a variac. A question about the pressure pad - should it have some foam rubber behind the surface that is in contact with the tape?

29th Jul 2019, 10:20 am	#10
SteveCG Nonode Join Date: Jun 2009 Location: Herefordshire, UK. Posts: 2,495	Re: Grundig TK120 tape recorder Right, The tape recorder plays back. I've not attempted 'record' yet. A brief check of the HT voltages puts them about right - but I shall check in more detail. Progress.

29th Jul 2019, 10:27 am	#11
Uncle Bulgaria Nonode Join Date: May 2016 Location: Cornwall, UK. Posts: 2,330	Re: Grundig TK120 tape recorder If you're on the lookout for the little fuses, I get 80mA 250V slow-blow types from RS.

29th Jul 2019, 10:30 am	#12
SteveCG Nonode Join Date: Jun 2009 Location: Herefordshire, UK. Posts: 2,495	Re: Grundig TK120 tape recorder Uncle_Bulgaria - thanks for the fuse source advice.

2nd Aug 2019, 12:01 pm	#13
SteveCG Nonode Join Date: Jun 2009 Location: Herefordshire, UK. Posts: 2,495	Re: Grundig TK120 tape recorder Tried recording using a 5 3/4 inch spool of Standard Play EMI tape. That worked and it erased the previous recording. The bias oscillator frequency was 58.3 kc/s - I only had to hold my meter probe near the wires to the heads to get a reliable signal ! The only issue I have is that its rewind is lacking in power, probably due to the small rubber tyre on the motor spindle being shiny - I don't think it is a 'sticky-shed' issue. Fast forward is fine. A clean with IPA - or will I have to roughen the surface of the tyre?

6th Aug 2019, 12:44 pm	#14
Tractorfan Dekatron Join Date: Mar 2008 Location: St. Frajou, l'Isle en Dodon, Haute Garonne, France.(Previously: Ellesmere Port, Cheshire, UK.) Posts: 3,182	Re: Grundig TK120 tape recorder Hi, Dad bought a TK120 back in 1967. And it has given us many years of fun and memories. I have now 'inherited' it, and it still works well. I only had to replace the EM84 and the ECL86 many years ago. I think it's even still on its original belt! The rewind always was mediocre at best, and it was down to the rubber wheel having insufficient traction against the L.H. plastic turntable. I used to ease the spindle slightly to the right with my finger nail to improve matters. More recently, I found a flat rubber belt (I know not from where) that fitted snugly around said turntable. The rewind function is now much more brisk! Cheers, Pete. Attached Thumbnails __________________ "Hello?, Yes, I'm on the train, I might lose the signal soon as we're just going into a tunn..."

6th Aug 2019, 12:54 pm	#15
SteveCG Nonode Join Date: Jun 2009 Location: Herefordshire, UK. Posts: 2,495	Re: Grundig TK120 tape recorder Pete, a thin flat rubber band eh - what good, lateral thinking! I'll look out for one.

16th Aug 2019, 11:21 am	#16
SteveCG Nonode Join Date: Jun 2009 Location: Herefordshire, UK. Posts: 2,495	Re: Grundig TK120 tape recorder Pete (Tractorfan), I came across some discarded rubber bands - 'standard issue' Royal Mail I believe. These are nearly the right dimensions, so I tried out your suggestion. The rewind was certainly a lot better, however the tension of the band on the reel holder was not quite enough to hold it on for long. So as part of experimentation I'm thinking that I could cut out about 10% of the band and glue it together again. I have read on the forum of superglue being successfully used on drive belts, but since I have found that superglue containers once opened tend to ooze - no matter what you try doing to stop it - I am proposing trying UHU glue, which I already have.

18th Aug 2019, 9:27 am	#17
Tractorfan Dekatron Join Date: Mar 2008 Location: St. Frajou, l'Isle en Dodon, Haute Garonne, France.(Previously: Ellesmere Port, Cheshire, UK.) Posts: 3,182	Re: Grundig TK120 tape recorder Hi, Glad my suggestion bore fruit for you. I can't remember whether the band I fitted was snug enough to grip the turntable, or whether I used a bit of glue. The rewind was sluggish, even from new, and it would be interesting to know if other machines of that range were the same. Anyone? Cheers, Pete. __________________ "Hello?, Yes, I'm on the train, I might lose the signal soon as we're just going into a tunn..."

19th Aug 2019, 10:30 am	#18
SteveCG Nonode Join Date: Jun 2009 Location: Herefordshire, UK. Posts: 2,495	Re: Grundig TK120 tape recorder Yes, thanks Pete. I've yet to try the gluing experiment, its on the round-tuit pile. However I was thinking of using a Bib tape splicer, with its two pads, as a way of holding the band in place while the glue sets. I'll update the results. A question Pete: - does your machine use any foam rubber in the tape pressure pad? Mine does not, but I'm not sure that Grundig ever used it.

21st Aug 2019, 7:43 pm	#19
Tractorfan Dekatron Join Date: Mar 2008 Location: St. Frajou, l'Isle en Dodon, Haute Garonne, France.(Previously: Ellesmere Port, Cheshire, UK.) Posts: 3,182	Re: Grundig TK120 tape recorder Hi Steve, Not foam rubber. I think it's a felt pad on a springy brass strip. I can't be 100% certain, but I'll whip the cover off and have a shufty next time I get a minute. Cheers, Pete. __________________ "Hello?, Yes, I'm on the train, I might lose the signal soon as we're just going into a tunn..."

22nd Aug 2019, 12:41 pm	#20
SteveCG Nonode Join Date: Jun 2009 Location: Herefordshire, UK. Posts: 2,495	Re: Grundig TK120 tape recorder Thanks Pete. I tried the splicing experiment. It all worked nicely - except that UHU is just not strong enough. So I'll try superglue - when I have something else that needs it (read post no. 16 for why). BTW: The Bib splicer is actually a cassette tape splicer and I used a cut-off section of the polythene wrapper from a Radio Times as an outer sandwich to keep the glue off the actual splicer.