Grundig TK 35 Drive Belt Replacement

[DMcMahon]

After a few diagnostic tests proved beyond doubt that the hum issue on Playback was coming from the EF86/ECC83 pre-amp area and fixed it by refitting the L shaped metal screening cover that fits over those 2 valves. Had removed the cover for replacing the various capacitors.

Of course made no difference to the very weak recording on playback.

Checked the erase and record signals, they were good, 350 volts p-p 76kHz erase signal at the erase head and 540 volts p-p 76kHz at the record head (combined record/play).

Signals were clean and stable frequency wise, but there was some voltage amplitude instability at times. Replaced paper capacitors C3 and C5 at the Bias Oscillator (both leaky) this fixed the voltage instability.

Still no change to the very weak recording.

Monitored the record signal going to the record head, as always difficult to clearly see the signal modulated onto the much larger HF record bias. I killed the bias (removed the
EL95) and then could see a good record signal exiting R26 going to the record head.

Next will try cleaning the heads again and try another tape to see if can get a better recording, either way I think then I will park this machine to be able to get on with many other outstanding jobs.

[hillmanie]

Yes, Old Robinson will, like the poor, 'be always with us'. Hubbel was successful Yank sparks it seems and his stuff went worldwide. Where I worked he was king. i note that the plugs and sockets are widely available and if bigger than the Grundig originals are at least better than our otherwise admirable 3-pin fused
TT

[DMcMahon]

Recleaning the heads made no difference to the very quiet recordings. But trying another tape made a huge difference, got very good results, tried a couple of other tapes to make sure not just a fluke and also got good results with them.

So the original tape appears no good, so heading for the bin. It was just a random old tape that I picked out of many to try on the TK 35.

I have a very large number of tapes and this experience re-enforces what I have been saying to myself for some time, that I should make time to make some reference tapes with music recorded, at various speeds, mono/stereo, 2 /4 track etc and catalogue them so that when I am testing, I have an appropriate tape that I know is good both for playback and recording.

[David001]

Well done getting it going!

[hillmanie]

Re tape quality, this is not news to the majority here but I note that new unused tapes, some professional some domestic appear on eBay. Being a bit wary of 'new old stock' 30yr old old new stock, I enquired off one seller and no, they were not of recent manufacture.
T

[DMcMahon]

Yes I think the NOS (New Old Stock) term is very erroneous, often the item/s can be vintage age so very old, some items of this age may be fine but for tapes, capacitors, rubber components etc they potentially may have degraded, so may be far from new condition, I have always said a more honest term would be UOS (Unused Old Stock) but of course the "New" in NOS is what attracts people.

The tape in question was probably very old and very used and of unknown make/origin.