Grundig TK245 overhaul

[Panrock]

I've now fitted a new 3-core mains lead, replacing the original 2-core one. I haven't yet megger tested the mains-chassis leakage. This presumably must have been originally expected to be pretty good.

I notice there's a round-section belt sitting there under-decks. It may be OK - I don't know what it does (I'm a novice, remember) or how floppy it should feel.

I've discovered a long-forgotten bin in my stores marked 'belts'. Who knows what wonders it contains - or not.

Steve

[DMcMahon]

I think the round rubber drive belt must be the tape counter drive, often counter drive belts can stretch and be somewhat slack and still perform OK.

Looking at the 2 fibre/fabric flat belts in the Service manual they do look slack, particularly the Supply spool belt, so as Ben says they may well be OK. Cannot really see what could tension them.

[ms660]

The belt should be tensioned when the reel table moves outwards.

Lawrence.

[Techman]

Originally Posted by Reelman

If the belts are fabric one side and rubber the other then they are similar to the ones used on Telefunken recorders made more than 10 years previously, eg KL65.

Yes, that's exactly what I was thinking.

I certainly wouldn't be going to all this trouble with mains leads and belts until I'd given it full mains to prove that it was actually capable of working, although perhaps you already have. The Telefunken, which this Grundig seems very similar to, are known for the heads going o/c for no apparent reason, which if this is the case, then it's a 'no goer'! Stick an old pre-recorded tape on it and test the state of play before going any further with it. It doesn't matter if the take up and winds aren't working as you can turn the spools with your finger for a short test. If there's no audio output then do a quick test to see why - record / playback switch contacts dirty or not operating properly, open circuit head, open circuit speaker (yes, I've had that one), no HT etc. etc. I've worked on hundreds of these old tape recorders and my tests are always the same - then unpug from the mains and have a feel of the smoothing can for any signs of warming, just in case

[Welsh Anorak]

I rather like the look of that machine - like an upmarket version of the TK124 - 144 series. I assume it takes 7" spools? The sound will probably be quite good as I think I see a tweeter lurking in there. Was it rare in this country? I notive the controls are labelled in German.

[Panrock]

Yes, it takes 7-inch spools. Yes, there's a tweeter in there. The sound should be good!

There's absolutely zero hum on the resting speaker, but hum comes up when I put my fingers around the heads area, so the HT electrolytics must be good.

The 'magic eye' indicator is illuminates brilliantly, but on 'record' only. So again, the HT must be present.

Touching the rear connections to the playback head results in healthy hum. Putting an Avo across the head, in situ, reads about 1100 ohms.

After cleaning the belts and some spooling back and forth, the take-up of the tape now seems to work.

The 3¾ and 7½ i.p.s speed selector works.

Playing with the track selector control has produced some mush in the speaker. This can be varied with the volume control. But nothing off the tape. The content of the tape is unknown.

From the crackles, the various selector switches and pots could do with cleaning, or at least exercise.

I think I've just heard some odd faint shuffling noises off the tape! I next need to try on a known good tape...

Steve

[Ted Kendall]

Remember to de-gauss the head after you've AVO'd it...that's probably the cause of the shuffling noises.

[Panrock]

Wow... thanks for that. The only degausser I have is for TV tubes. Not that it will help, but at least I tried the Avo both ways round... ;-)

[Welsh Anorak]

Bit late in the day, but it's not advisable to use an Avo to chech the continuity of heads, especially Bogen manufactured ones. The current is enough to burn them out. Luckily you seem to have been lucky, though as Ted K says, you will need to degauss them.
The magic eye probably isn't meant to illuminate in play - it doesn't in the 100 series.
It seems you might not need to do too much to get this machine working again!

[Panrock]

I live and learn. Thanks.

Anyway, I tried turning the tape over. I was then greeted with classical guitar music. And not only that: I could hear every squeak and pluck of the plectrum. Even out of the cabinet, the quality of this recording (at 3¾ips) is fantastic. It sounds every bit as good to my ear as a CD player. Plenty of natural bass too.

I shall try the recording function next. First though, the reliability of the 'play' spool take-up is still a bit iffy. It looks like I shall have to remove the right 'platter' to investigate what drives it. How does this come off? Thanks.

[DMcMahon]

You are making good progress Steve, well done.

I think the complete reel tables are secured by a single e-clip/circlip on the underside.

Take careful note of the order of the reel table parts, there can be more than 1 type and thickness of clutch flat washers fitted, check the clutch felt ring for cleanliness.

[Techman]

Yes, as said, be careful measuring the continuity of the head with any sort of meter - if done at all it should be done with a high(ish) value series resistor to limit any current to an almost insignificant value.

You'll definitely need to now demagnetize the heads before playing any more tapes, as the residual magnetism will degrade the recordings on them as they're playing - and you don't want to be doing that. You can do a basic demagnetization by switching the machine on and once the valves have warmed up, with all controls, volume/mic gain etc., turned right down and without a tape fitted, set the machine to record. Once recording without any tape, pull the plug out from the wall socket without touching any of the controls on the machine. The bias oscillator gradually dying away as the HT dies and the valves cool will remove some of the magnetism from the head core - you may need to repeat this a number of times. All this is assuming that the machine is actually capable of recording and the bias oscillator is working.

[Panrock]

That's a really handy method to 'fish me out of it' - thanks!

I clearly committed a cardinal sin in applying the Avo, for which I apologise. However (assuming 1½v from the Avo on its mid-range and no DC path shunting the head) then it does seem amazing that just over 1mA through the head can burn it out. It must have incredibly fine wire.

Useful info on the reel table. I'll take a look this morning.

[Panrock]

Here's the bottom circlip holding the reel table, before - and after - my attempt to remove it.

Oh dear...

The remnant is proving hard to shift.

[Reelman]

Oh hard luck Steve, that is unfortunate! However it looks like it will still hold so if you can prise it off it may be reusable. After all since the machine can only be used horizontally it is not subject to much strain. You will notice how Grundig used circlips based purely on friction rather than snapping into a slot on the spindle. I bet they are an absolute pig to replace without the correct tool, see the recent thread on circlip pliers and the source of.

I bet somebody here may have some spares, I might be able to find one myself, I tend to pull them off with a pair of pliers.

Peter

[Panrock]

Thanks for the commiserations... really nice to know of the support out there.

I have just got the circlip off. Don't ask how. I'm not even sure myself, but sheer butchery and brute force was involved. (It's at times like these I'm glad I'm not a dentist!).

More to come...

[ben]

In my experience there's not often a need to remove the spool carrier. Most of the time poor take up is due to what is /isn't happening with the drive on the upper deck. Anything rubber is likely to need resurfacing or replacing; anything that shifts will need lubricating - so I'd start there.

[Panrock]

Here are the views, in order, as I have taken things apart. The first picture is below decks, the remainder above.

I guess 'lubricating and cleaning' comes next. I'll have a think about resurfacing...

[Panrock]

The round stationary plastic thing at the bottom, with pad inserts, seems to be OK going back either way round. The pad inserts can be put back bottom sides up, to make them completely like new again.

There seems to be no obvious way to adjust the friction, which is currently insufficient.

[Reelman]

You will note that each pad can occupy one of 3 positions, that is how the friction is adjusted.
According to Grundig asymmetrical placement (as present) is ok. As mentioned reverse them for a better surface.

Peter