Translate

Sunday, 10 July 2016

Grundig TK120 repair

Gareth (a fine chap from the motherland) walks into the workshop with a bin bag under his arm....

"My Father-in-law's dug this tape recorder out of the attic. It's got a recording of him on it, but he says there's no sound. Can you have a look?"

Yeah ... why not?

It's a Grundig TK120, in distressed condition. It looks like it's been left rather too close to the fire!















... and after removing the tape and the top cover, the immediate issue is all the rubber parts have disintegrated....










Now the belts are no real problem... but the drive idler tyre is going to be...

After some head scratching, and some looking about for suitable parts, an O-ring is super-glued to the remaining idler wheel....







Now to replace the belts. So I unscrewed the four screws with blobs of paint on, to remove the top plate. DO NOT DO THIS!

FATANG! All the spring loaded control levers fired out of their mounts.... Thankfully their positions are quite simple to work out, but very fiddly.... several hours later and the thing is back together....

Here's how it should have been done!..


Underneath the deck is a small plate, with two screws... undo those to gain access to the bottom of the capstan flywheel....


... and work the belts about the bottom of the flywheel, through the small hole. It's still fiddly, but much less agro than re-aligning the top mechanism!



















You'll need to remove the take-up reel and clutch to replace the take-up drive belt. The belt itself is straight forward. The clutch reassembly is a bit tricky...

This is the bottom of the deck, showing the new tape counter belt... Remove the little pulley and it's clip from the take up reel shaft. There's another clip underneath and an antifriction washer. Remove those.




Turn the machine up the right way, and remove the take up spool...











This will reveal the take up clutch, and it's little three pads... if they've fallen out, don't panic... they'll be there somewhere!










Fit the belt and reassemble the clutch. Some adjustment of the clip above the small pulley we removed earlier may be required to get the right amount of friction on those pads, but it's not difficult.

The motor was a little sticky on this machine. I stripped the lower bearing off and re-lubricated it. It now spins like a top....

... there's still no sound.


This is rapidly traced back to an open-circuit HT fuse, it's replaced and there's some audio briefly. The HT (and heaters) is provided from two extra windings on the motor. There's no transformer. Clever stuff. Garrard and BSR used a similar trick on their record changers in the 60's. The electronics are a simple design with just two valves, an ECC83 and an ECL86.

The main smoothing capacitor is getting warm. A sure sign that it's had it day. It's a two section 50uF+50uF 350V part. I replace it with two suitable caps.









Switching back on and there's audio again... but it rapidly fades.... A check round the other caps proves their innocence... I'm not liking the look of the getter flash on the top of the ECL86 triode-pentode valve though, it looks like it's had a hard life.... The getter flash should be sliver or black looking, and should have nice sharp edges...





This is sort of brown looking....













... and checks on the avo valve tester show the triode is very low at 0.6 mA/V (It should be 1.5 when new) and the pentode section won't read at all! When testing the pentode section, there's a blue glow inside the anode structure, a sure sign there's some gas in there. A replacement restores operation, and the dulcet tones of a young man playing the guitar once again issue forth from the speaker... recorded some 50 years ago!


Audio quality isn't fantastic. These machines were a bit of a domestic novelty really. After transcribing the contents of the tape, Gareth described the quality as "Like a walkman with flat batteries", which isn't a bad description at all...

1 comment:

  1. Thanks for your advice, I fixed my set using your instructions! Cheers. Nick

    ReplyDelete