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Vintage Tape (Audio), Cassette, Wire and Magnetic Disc Recorders and Players Open-reel tape recorders, cassette recorders, 8-track players etc.

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Old 13th Oct 2021, 10:15 pm   #1
DMcMahon
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Default Grundig TK 146 Reel to Reel Check Out

Brought this around 2 years ago but never found/made time to check it out properly, other than a little work in this Thread :-

https://www.vintage-radio.net/forum/...d.php?t=169920

Checking it out properly now as want to sell it.

Circa 1970 solid state, single speed 4 track, mono recorder, very similar to the TK 141 with the addition of EOT (End Of tape) sensor, switchable manual/auto recording & Trick (superimpose) recording.

Loaded a 5 3/4" tape (max spool size) and tested the tape transport operation. Fast wind in both directions works very well from end to end of the tape, EOT operation works well but no Play as no drive to the Take Up table.

Found the drive belt from the flywheel to the Take Up table was broken.

Apart from the single break the belt from a distance looked OK but close inspection showed that it had serious cracks completely around the whole belt, very obvious when the belt is stretched.

Belt (round profile) measured around 2.3mm x 90mm ID, replaced it with closent I had, a new Sony 377 2mm x 90mm belt.

The tape counter belt also is very badly cracked, it does work but I will replace it.

Playback, pause etc now work well. Playback sound works OK but a big problem with the volume, the sound volume dramatically changes when tape is playing, any very light touch or disturbance of the board with the 3 slider controls can make the sound come and go.

Not sure yet if it is a slider problem, will try contact cleaner on them and check the soldered connections on the back of the board.

David
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Old 14th Oct 2021, 9:30 am   #2
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Default Re: Grundig TK 146 Reel to Reel Check Out

While testing fast winding there was an intermittent clicking noise which turned out to be the tape counter where one or more of the counter segments were sticking, will clean/lubricate the counter as required.

David
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Old 14th Oct 2021, 3:19 pm   #3
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Default Re: Grundig TK 146 Reel to Reel Check Out

Visually checked the soldering and cable connections to the slider board and nothing obvious bad. Tried contact cleaner on the volume and tone sliders both of which are very sensitive to affect the volume, but no change.

Some time later found now there is zero sound, wondered if I may have shorted something (do not think I did) when working live and touching/disturbing the connections on the board, so checked the 3 fuses on the rear panel.

The 100mA fuse had a loose end cap and measured various readings so replaced, still no sound.

So need to do some monitoring on the main board which looks awkward.

David
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Old 14th Oct 2021, 8:26 pm   #4
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Default Re: Grundig TK 146 Reel to Reel Check Out

Found there was a fourth fuse Si 4 (630mA) on the main board fusing the +17 volt to the output amplifier but this and all the DC supplies checked out OK.

Using scope proved that the audio signal was getting to the slider board but not leaving the slider board. While trying to see why, the audio started working again to the speaker
but kept coming and going intermittently. Could not conclusively see what was happening, but it looked like the volume control slider was intermittently going open circuit.

Trying to measure the slider in-situ gave inconsistent results so removed it to retest further. Had quite a struggle getting it out, it was soldered in by its 9 legs and my solder sucker really struggled and the legs were a tight fit in the holes.

4 of the legs are just the metal case fixings, 3 of the legs are the 100k log slider and the other 2 legs measure as 35k and their resistance varies wrt the wiper of the 100k slider with zero being around the middle position of the slider and either side of the middle the resistance increases up to the 35k when slider moved in that direction, these 2 extra slider legs are shown on the schematic but I do not really understand their function.

Measuring the resistance of the main 100k slider using AVO I could not fault its operation and no obvious sign of it going open circuit during operation, same for the 35k operation.

It does feel stiff and graunchy in operation so for that reason I am going to replace it, taking the part from my TK 141 (#2, # 1 sold) which is basically a spares machine, the TK 141 volume slider works well (in the TK 141) and feels very smooth in comparison.

David
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Old 14th Oct 2021, 8:42 pm   #5
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Default Re: Grundig TK 146 Reel to Reel Check Out

I believe that the tapped volume control provides the “loudness” function of boosting bass and to a lesser extent treble at low volumes. One of the reasons why this range of Grundigs provides such a pleasant sound. The TK146 was my first Grundig back in 1971.

While you have the case off David have a think about replacing the roller on the main mechanical switch which provides the dedents. After lasting for 50 years they are now giving up the ghost! When the roller goes the mechanical switch will stick in the rewind position. Any TK of this period described as “not working” on eBay will usually have this problem and easy to see in a photograph.

Peter
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Old 14th Oct 2021, 8:49 pm   #6
DMcMahon
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Default Re: Grundig TK 146 Reel to Reel Check Out

Peter, thank you that makes sense now.

In Post 6 of the linked Thread at Post 1 of this Thread I reference having to replace the roller cam making one from wooden dowelling.

David
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Old 14th Oct 2021, 8:55 pm   #7
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Default Re: Grundig TK 146 Reel to Reel Check Out

I thought that you might already be aware of the roller problem, it is very common.

The ones I see advertised now seem expensive for what they are, I have previously published the name of a guy who supplies these at a good price…. His name escapes me at present.

Peter
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Old 15th Oct 2021, 9:43 pm   #8
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Default Re: Grundig TK 146 Reel to Reel Check Out

Transplanted the volume control slider from the TK 141 to the TK 146.

Now the TK 146 volume is working very well, cannot get it to go bad, looks like it is fixed, time will tell

Did quick microphone recording test, worked well. With the case removed from the chassis in order to do microphone recording, you have to manually pull back and hold the microphone selector slider switch near rear of the main board.

With the case fitted, to access the microphone DIN socket there is a spring loaded cover plate over the socket that has to be pulled back to insert the microphone connector, this also pulls back the microphone selector switch.

David
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Old 16th Oct 2021, 1:30 pm   #9
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Default Re: Grundig TK 146 Reel to Reel Check Out

Started checking out line recording into the Diode DIN socket.

First checked automatic recording which works very well, the VU meter typical reading during recording is around 50 peaking to around 70 on very loud music. For manual recording it says to adjust the record level slider to get a reading of 70, maximum on the VU meter being 90. Playback of the automatic recordings is good.

On manual recording the VU meter goes hard over even with the record level slider at minimum as if the record level slider is not working but a quick resistance check indicates that the slider is working. For the slider wiper to be in circuit contact au 1 has to be closed when switched to manual or trick recording, so next will check the 3 contacts of the auto/manual/trick recording switch. Also will check the wiring connections to the record slider, because the slider board was worked on yesterday for the volume slider replacement.

David

Last edited by DMcMahon; 16th Oct 2021 at 1:37 pm. Reason: Typo correction
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Old 17th Oct 2021, 11:46 am   #10
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Default Re: Grundig TK 146 Reel to Reel Check Out

Record level slider and connections all checked out all OK.

Checked the 3 contacts actuated by the Record switch 3 positions, found the manual record contact au 1 was making good mechanical contact when record button pressed down (and manual or trick recording selected) but had very poor electrical contact (very high resistance). Cleaned up the contact and now all good.

Line recording (tape out from Hi-Fi amp) with a straight connected cable was too strong and resulted in distorted recordings either with low record level setting in manual recording or automatic recording.

Using a 220k resistor attenuated cable gives very good manual recordings, with a typical record level around 2.5, similar with 470k. Had previously used the 220k cable when good automatic results obtained.

Replaced the badly cracked tape counter drive belt. Original round section belt was around 1.8mm x 80mm ID which was fairly slack, used a square section 1.7mm x 70mm which is working well.

After a bit of cleaning and lubrication have re-assembled it but struggling to locate the lid and carrying handle, found about 8 other carrying handles and at least 15 other lids.

David
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Old 18th Oct 2021, 12:46 pm   #11
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Default Re: Grundig TK 146 Reel to Reel Check Out

Tested the external speaker output all OK and also tested the output signal at the Diode DIN out to external amplifier.

After much searching located the carrying handle and a lid, I think this lid is from the TK 141 because it is somewhat tatty, will keep searching for the better condition TK 146 lid.

David
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Old 18th Oct 2021, 2:07 pm   #12
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Default Re: Grundig TK 146 Reel to Reel Check Out

Replaced the badly cracked tape counter drive belt. Original round section belt was around 1.8mm x 80mm ID which was fairly slack, used a square section 1.7mm x 70mm which is working well.
David[/QUOTE]

I had the same problem with mine, using the 2mm 83mm replacement belt from a pack of three bought online, the counter belt was too loose.

I tried a few other belts I had and discovered that the machine is quite sensitive to counter belt tension, if it is too tight the RH spool does not move left enough during FF. Eventually found a suitable belt that worked albeit smaller cross section. There is little drive load on this belt so it should be durable enough

Best Regards
Chris
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Old 18th Oct 2021, 4:03 pm   #13
DMcMahon
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Default Re: Grundig TK 146 Reel to Reel Check Out

Yes I had first tried I think a 1.8 x 70mm round section belt which worked fine for the counter but now and again Play and FFD struggled due to the counter belt being a little over tight and making the Take Up clutch slip.

David
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Old 21st Oct 2021, 6:42 pm   #14
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Default Re: Grundig TK 146 Reel to Reel Check Out

Replaced my homemade wooden cam roller for the Function switch selector by the homemade nickel plated brass spacer covered with silicone tubing cam roller that unitelex provided, looks much more professional (and works well) than my wooden effort.

David
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Old Yesterday, 4:45 pm   #15
DMcMahon
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Default Re: Grundig TK 146 Reel to Reel Check Out

After more fruitless searching for the lid, I eventually realised that the lid was missing when I originally purchased it (so memory of it being in good condition was erroneous), so have cleaned up the TK 141 lid to go with it.

Found the original microphone that came with the TK 146, a Grundig GDM 314 but when tested found the microphone is completely dead, all connections at the DIN connector and the microphone are intact. Looks like the microphone transformer is in the DIN connector but it only has 3 wires ?

I will use the Grundig GDM 18 microphone tested earlier to go with the unit.

This leads onto a question I have often wondered about. There are 2 outputs on most of the various microphones, on pins 1 and 3, with the output on pin 3 being around 1/10th of the output on pin 1. You can see this on the attached microphone drawing.

On the Grundig recorders microphone DIN connector pin 1 is the live pin normally used. On older recorders that use the old condenser microphones pin 3 is used as the live. But have never understood why there is the second lower output signal on pin 3 for the Grundig dynamic microphone, I am sure someone will know.

David
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