Grundig TK20 reel to reel tape recorder - UK Vintage Radio Repair and Restoration Discussion Forum

Tony Gutteridge · 25th Nov 2019, 2:42 pm

I have a Grundig TK20 tape recorder which I have had since the very early 60’s. This works perfectly although the volume control needs to be at maximum to hear the recordings. Does it need a new amplifying valve and if so is it difficult to replace?

Edward Huggins · 27th Nov 2019, 1:32 pm

It is highly unlikely to be a valve replacement issue - if only it were that easy!

I suggest the playback head is dirty/worn - and/or there is a low HT supply.

What is your level of experience is servicing or fault finding on these vintage R2R machines?

Phantomrose1999 · 30th Nov 2019, 4:31 am

I would connect a PC output put to the input and test the volume. If using another input source the audio is loud, then the problem will most likely be a worn or corroded head.

If the volume is low with the PC input source, then i would check the voltage after the main filter caps, if low, most likely the old rectifiers will need to be replaced, as they can drop the output voltage over time.

If it has not worked for a while, the original motor run capacitors will surely fail.. just a question of when.

radiotechnician · 1st Dec 2019, 7:53 am

Is it possible that the tape on the spool has been wound
or creased so the shiny side faces the head ?

TIMTAPE · 1st Dec 2019, 12:42 pm

Another check along those lines is the felt pressure pad on the head (if it has one. I think some Grundigs used a taught band instead) It may have fallen off due to old adhesive or needs replacement anyway.

radiotechnician · 2nd Dec 2019, 11:38 am

I've worked on the TK20 as it was a model common in the 1960s.
I distinctly remember the condenser mike.

If the music and words on the tape can be heard distinctly under a
hum and hiss, the head is OK, and a contact or dirty valve pin might be
suspect.

With a blank take, a recording might be tries, to see if speaking
into the microphone causes the EM 84 to deflect.

Below is a peek at the description in Hickman, 3rd ed., Magnetic
Recording Handbook.

ricard · 2nd Dec 2019, 1:50 pm

One of the first things I'd check on a machine of this age would be the coupling capacitors. Grundig tended to use Wima in those days, which (among other manufacturers) are notorious for increased leakage with age, leading to incorrect valve biasing with consequent low volume, scratchy volume control, distortion, complete silence and output transformer overheating depending on how severe the problem is.

Edward Huggins · 5th Dec 2019, 12:16 pm

It's 12 days since the OP posted, but there's been Radio Silence since.
I hope we've not scared him off with all of these optional suggestions.....?!

Station X · 5th Dec 2019, 1:28 pm

The OP hasn't visited the forums since he posted. This is not uncommon I'm afraid.

There's no need to discuss this any further.

25th Nov 2019, 2:42 pm	#1
Tony Gutteridge Retired Dormant Member Join Date: Nov 2019 Location: Gillingham, Kent, UK. Posts: 1	Grundig TK20 reel to reel tape recorder I have a Grundig TK20 tape recorder which I have had since the very early 60’s. This works perfectly although the volume control needs to be at maximum to hear the recordings. Does it need a new amplifying valve and if so is it difficult to replace?

27th Nov 2019, 1:32 pm	#2
Edward Huggins Dekatron Join Date: Sep 2015 Location: Southwold, Suffolk, UK. Posts: 8,336	Re: Grundig TK20 reel to reel tape recorder It is highly unlikely to be a valve replacement issue - if only it were that easy! I suggest the playback head is dirty/worn - and/or there is a low HT supply. What is your level of experience is servicing or fault finding on these vintage R2R machines? __________________ Edward.

30th Nov 2019, 4:31 am	#3
Phantomrose1999 Hexode Join Date: Mar 2008 Location: Melbourne, Victoria, Australia Posts: 289	Re: Grundig TK20 reel to reel tape recorder I would connect a PC output put to the input and test the volume. If using another input source the audio is loud, then the problem will most likely be a worn or corroded head. If the volume is low with the PC input source, then i would check the voltage after the main filter caps, if low, most likely the old rectifiers will need to be replaced, as they can drop the output voltage over time. If it has not worked for a while, the original motor run capacitors will surely fail.. just a question of when.

1st Dec 2019, 7:53 am	#4
radiotechnician Pentode Join Date: Jan 2013 Location: Powell River, British Columbia, Canada. Posts: 217	Re: Grundig TK20 reel to reel tape recorder Is it possible that the tape on the spool has been wound or creased so the shiny side faces the head ? __________________ Steve Dow VE7ASO

1st Dec 2019, 12:42 pm	#5
TIMTAPE Octode Join Date: Jul 2006 Location: Perth, Western Australia Posts: 1,969	Re: Grundig TK20 reel to reel tape recorder Another check along those lines is the felt pressure pad on the head (if it has one. I think some Grundigs used a taught band instead) It may have fallen off due to old adhesive or needs replacement anyway.

2nd Dec 2019, 11:38 am	#6
radiotechnician Pentode Join Date: Jan 2013 Location: Powell River, British Columbia, Canada. Posts: 217	Re: Grundig TK20 reel to reel tape recorder I've worked on the TK20 as it was a model common in the 1960s. I distinctly remember the condenser mike. If the music and words on the tape can be heard distinctly under a hum and hiss, the head is OK, and a contact or dirty valve pin might be suspect. With a blank take, a recording might be tries, to see if speaking into the microphone causes the EM 84 to deflect. Below is a peek at the description in Hickman, 3rd ed., Magnetic Recording Handbook. Attached Thumbnails __________________ Steve Dow VE7ASO

2nd Dec 2019, 1:50 pm	#7
ricard Octode Join Date: Mar 2006 Location: Lund, Sweden Posts: 1,632	Re: Grundig TK20 reel to reel tape recorder One of the first things I'd check on a machine of this age would be the coupling capacitors. Grundig tended to use Wima in those days, which (among other manufacturers) are notorious for increased leakage with age, leading to incorrect valve biasing with consequent low volume, scratchy volume control, distortion, complete silence and output transformer overheating depending on how severe the problem is.

5th Dec 2019, 12:16 pm	#8
Edward Huggins Dekatron Join Date: Sep 2015 Location: Southwold, Suffolk, UK. Posts: 8,336	Re: Grundig TK20 reel to reel tape recorder It's 12 days since the OP posted, but there's been Radio Silence since. I hope we've not scared him off with all of these optional suggestions.....?! __________________ Edward.

5th Dec 2019, 1:28 pm	#9
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,289	Re: Grundig TK20 reel to reel tape recorder The OP hasn't visited the forums since he posted. This is not uncommon I'm afraid. There's no need to discuss this any further. __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.