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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 28th Jan 2020, 8:02 pm   #101
DMcMahon
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Default Re: Grundig TK 819 Any Useful Info

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Originally Posted by Boulevardier View Post
Would be sensible to allow the contact cleaner a while to evaporate before giving up on it...
Yes totally agree.
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Old 28th Jan 2020, 9:19 pm   #102
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Default Re: Grundig TK 819 Any Useful Info

Found another 2 paper capacitors hiding under the heads mounting plate, so will change them to be consistent. To remove the plate, had to remove 4 securing screws, 2 of which were also securing 2 little metal twisted arms that have a tiny little coil at the end.

The end of one of the metal arms broke off when screw removed so will have to repair that later.

The parts list calls the coils "kompensationsspule" (compensation coil). On the schematic they are shown wired in series with one side of the Playback heads (combined Playback/Record heads), do not currently know what sort of compensation the coils provide.

With the heads assembly removed, it is a good opportunity to clean all around the capstan motor, which is very dirty and somewhat corroded.
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Old 28th Jan 2020, 10:20 pm   #103
Leon Crampin
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Default Re: Grundig TK 819 Any Useful Info

The coils are for hum cancellation. They can be moved around so that the hum induced in them is equal and opposite in phase to that picked up by the playback heads. There is also a humdinger pot in the 6V heater supply to the first amplifier stage.

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Old 28th Jan 2020, 10:54 pm   #104
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Default Re: Grundig TK 819 Any Useful Info

Thank you Leon, good to know that the coils are for hum cancellation, so I guess that is why they have those strange twisted arms (for adjustment).

I did know about the humdinger pot, but currently am struggling to see the pot on the 819 schematic.

David
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Old 28th Jan 2020, 11:13 pm   #105
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Default Re: Grundig TK 819 Any Useful Info

As I recall, the 6V winding emerges from the transformer as a twisted pair, running directly to the pot which is on the side of the chassis below the EFxxx valveholder. Short wires link the pot to the valve heater pins. It's shown on the TK820 diagram I have.

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Old 29th Jan 2020, 10:48 am   #106
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Not 100% certain, but at this stage I would say there is no humdinger pot on the TK 819 which would agree with the TK 819 schematic (pot not shown) and the part list (no obvious pot listed).

I thought there was previously, but the pot I was thinking about is the nearby pot behind the Magic eye valve for the Magic Eye adjustment. I had also seen it in the TK 820 schematic previously so assumed that it should be the on the TK 819.

There are 2 green wires leaving the H1 winding of the transformer so they (if no pot fitted) should go direct to the EF 804 heater filament connections but very difficult to physically follow the green wires.

There is an EF 86 valve fitted in the EF 804 position, I have yet to check out the differences/compatibility of the 2 valves.

Presently struggling quite a lot checking the wiring at the valve base (to check the filament wires) for 2 reasons, the microphone transformer covers quite a lot of it and also there is an outer quite large elliptical connection base around the inner valve base, I am not sure yet if this is all one valve base or 2 separate parts.

Last edited by DMcMahon; 29th Jan 2020 at 10:50 am. Reason: Typo
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Old 29th Jan 2020, 11:56 am   #107
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Default Re: Grundig TK 819 Any Useful Info

Now checked out the EF 804 (actually an EF 86 fitted) filament heater wiring connections fully. There is definitely no humdinger pot fitted.

The 2 green wires I was previously chasing were the wrong wires due to me getting brau and braun mixed up in my mind.

Using the TK 820 manual it shows the colours of the various windings of the mains transformer (which I assume most likely is the same transformer used in the TK 819).

The 6 volt H1 winding (which the schematic shows connecting out to the EF 804) are blue (shown as blau) wires at the transformer. But because initially I got blau and braun mixed up, I looked at the brown wires (braun) which connect to a little terminal strip where the 2 green wires connect to the 2 transformer brown wires, but this is for the 24 volt output.

Now looking at the correct blue wires they do not connect to the EF 804 but to other valve (s).

The transformer wires that connect to the EF 804 valve base are 2 white wires from the transformer, these white wires go direct (not via the terminal strip) to the valve base (first to the larger outer valve base connection then from there 2 little short wires to the inner valve base).

According to the transformer winding colours the white wires (weiß) are one of the two 6.3 volt secondary windings, so if this is correct then the EF 804 filament heater supply is 6.3 volt not 6 volt as the schematic shows.

The mains on/off switch has not recovered (not switching on) from the previous Supersolve spraying, so cannot currently switch on to measure the heater windings, to see if the white wires are 6 or 6.3 volt

Will exercise the switch more but if no sign of life will have to bite the bullet and fit a toggle on/off mains switch.

Last edited by DMcMahon; 29th Jan 2020 at 11:59 am. Reason: Typo
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Old 29th Jan 2020, 12:58 pm   #108
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Default Re: Grundig TK 819 Any Useful Info

Checked out the pin out differences between the EF 804 and the EF 86.

The G2 Screen grid and the G3 Suppressor grid are swapped over, plus the anode of the EF 86 is swapped over with one of the internal screen connections of the EF 804.

So this I assume must be why there is the large outer valve base connection ring to the inner valve base, i.e. like an adaptor to adapt the wiring to suit either valve.
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Old 29th Jan 2020, 3:16 pm   #109
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After numerous operations the mains on/off switch has now burst back into life and currently is working normally (hopefully it will stay that way).

Measured the 3 transformer secondary windings for the heater supplies:-

1. The 2 blue wires = 6.64 volts, according to TK 820 documentation this is a 6V supply.
2. The 2 black wires = 6.54 volts, according to TK 820 documentation this is a 6.3V supply.
3. The 2 white wires = 6.30 volts, according to TK 820 documentation this is a 6.3V supply.

The 2 white wires that go to the EF 804 valve are the lowest actual voltage, so this may mean that they are in fact the 6 volt winding, so not agreeing with the TK 820 documentation, but maybe of course the TK 819 transformer is not identical to the TK 820.

The EF 86 valve although getting the 6.3 volt heater supply and its filament measuring OK, it is not obviously lighting up (maybe one of those valves where it is very difficult to determine visually).

It is very slightly warming up after being on for some time, later will see if it actually operates.
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Old 29th Jan 2020, 4:55 pm   #110
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Default Re: Grundig TK 819 Any Useful Info

Glad your switch now works. For the transformer voltages, firstly check your mains voltage against the setting of the voltage selector. Are your figures loaded or unloaded?

The EF86 has a low consumption (0.2A) spiral wound heater to minimise hum. In the Grundig, it is underrun. The valve is well screened internally - Grundig also fit a can. It is quite possible therefore that in daylight, the heater glow may not be apparent.

If the valve is passing anode current, it's emitting electrons - or seriously shorted.

Leon.
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Old 29th Jan 2020, 5:02 pm   #111
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Default Re: Grundig TK 819 Any Useful Info

Thank you Leon, mains voltage setting is correctly set to 240. Metal screening can is currently off the EF 86. Results are loaded in terms of all the valves being plugged in, but valves themselves just idle.
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Old 31st Jan 2020, 6:06 pm   #112
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Found another 2 paper capacitors hiding under the heads mounting plate, so will change them to be consistent. To remove the plate, had to remove 4 securing screws, 2 of which were also securing 2 little metal twisted arms that have a tiny little coil at the end.

The end of one of the metal arms broke off when screw removed so will have to repair that later.

The parts list calls the coils "kompensationsspule" (compensation coil). On the schematic they are shown wired in series with one side of the Playback heads (combined Playback/Record heads), do not currently know what sort of compensation the coils provide.

With the heads assembly removed, it is a good opportunity to clean all around the capstan motor, which is very dirty and somewhat corroded.
Replaced the final 2 paper capacitors that were under the head mounting plate. Initially a little difficult to identify the LHS capacitor, but worked out that it is C28 a 0.1uF/500 volt. This connects between earth and G1/UIII contacts.

Had quite a job identifying the one on the RHS, it had black tape wrapped around it, when I removed the tape to read the capacitor value, all the writing on the capacitor body was no longer there/visible.

I measured its capacitance on my capacitance meter at around 220nF, by the previous (18) replaced capacitors mainly being around double their stated value, I thought that a good chance that it was a 100nF (0.1uF). For a comparison reading I checked its capacitance on my DMM and this indicated around 450nF.

Normally my 2 meters read very similar capacitance readings for the same capacitor, so strange that this particular capacitor gives 2 quite different readings.

Because the DMM indicated 450 I then wondered if the actual value should be higher than 100nF, so a little confusing.

After more detective work I deduced that this capacitor is C26 (across BII contacts) a 0.1uF (100nF/250 volt).
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Old 9th Feb 2020, 12:33 pm   #113
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Default Re: Grundig TK 819 Any Useful Info

After cleaning the transport chassis, fitted the chassis to the electrical chassis, then refitted the heads assembly to the transport chassis. Refitted complete chassis assembly back into the case, ready for first power up of complete unit (at long last).

While refitting the heads assembly looked at the little sprung loaded contacts that sit above the capstan motor shaft, on previous post had identified one of the contacts as GI, the other contact being GII. But previously had not looked further at their operational function.

Both contacts are normally made (normally closed) by the top common contact plate (which connects back to earth/ground). I could not see anyway how the contacts could be actuated to the open state, there is several mm gap between the top of the capstan motor shaft and the top contact plate and even if the shaft is manually lifted up (taking up its free play) still nowhere near making contact with the earthed contact plate.

Looking at the German schematic, GI connects the earthed top contact (in its normally closed state) through UIII contact to bottom side of "relais" (relay) C, the top side of relay C connecting to + 24 volts. So relay C will then energise (assuming GIII is in the closed state).

Note - U contacts are "Geschwindigkeits-Umschalter" (rate/speed selector/selection) for the tape speeds.

Relay C is identified as "Fliehkraft", which is centrifugal, so then the penny dropped a little. Looking more closely at the capstan motor shaft, there is a little smaller diameter piece at the top end. Using long nosed pliers I found this piece is a spring loaded plunger/shaft and can be manually lifted up against the spring by at least 5mm, enough I would say to push open the GI/GII contacts.

So I now assume that when the the motor shaft rotation speed gets to a certain level that centrifugal force will push up the sprung loaded plunger and open the G contacts. I say assume, it has got to be something very similar otherwise the contacts would never open. Looking forward to seeing the plunger lift up in operation.

Relay C has 2 sets of contacts CI and CII, both contacts controlling motor power. CII switches the 260 volt secondary transformer winding (have seen this referred to as "the over winding") through to the motor. Not 100% sure yet, but think this is used for the top tape speed.

Looks like CI contact switches the motor capacitors C38/C39, I think these are motor running as opposed to motor start capacitors but not 100% sure.

The second G contact GII, via UII and then via some other switch contacts can energise the "Ausgangsrelais" (Outputs relay) but not yet looked any further at what that actually is for.

Even though the GI/GII contacts are visually physically/mechanically made both contacts are not electrically making (determined by resistance measurement across the contacts).

So decided to strip the contacts down (rather than just try switch cleaning in-situ, both to inspect and gently clean the contacts with some very fine wet & dry/crocus paper.

Stripped the contacts down and dropped a couple of the small pieces inside the unit, which then refused to come out when unit shaken ! so had to remove the complete chassis assembly and after much shaking & looking found the dropped pieces (amazing how small items can hide).

The contacts visually do not looked damaged or pitted, just somewhat tarnished, so will now will clean them, re-test them and re-assemble the contact pieces to the removed head assembly, before putting it all back together.
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Old 9th Feb 2020, 9:59 pm   #114
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Cleaned up the contacts and measured each individual contact button face to its contact arm all OK. Re-assembled (not as easy as it sounds) but still having problem with one of the contacts (GI I think), good mechanical contact but no electrical continuity across the contact pair !!
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Old 9th Feb 2020, 10:12 pm   #115
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Sorry to be the bearer of sad tidings, but those heads look worn out - when I reluctantly retired my TK8 n years ago, the R/P head looked like that...
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Old 9th Feb 2020, 10:32 pm   #116
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Well that is not good news but will still press on and see how it performs, if I get that far.
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Old 10th Feb 2020, 9:36 am   #117
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Default Re: Grundig TK 819 Any Useful Info

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So I now assume that when the the motor shaft rotation speed gets to a certain level that centrifugal force will push up the sprung loaded plunger and open the G contacts. I say assume, it has got to be something very similar otherwise the contacts would never open. Looking forward to seeing the plunger lift up in operation.
That is correct, the idea is to supply the motor with a higher voltage while it is starting up, and then go to a lower voltage once it has reached its proper speed, I'm assuming to minimize motor power consumption and hence heat. This mechanism is only operational at the higher speed (7 1/2) however; at 3 3/4 the lower voltage is used all the time.

Can't really see in the picture, but it looks like it might be missing a little plastic top on the plunger to avoid it short circuiting the contacts to ground. It should be white-ish in color.
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Old 10th Feb 2020, 10:16 am   #118
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Thank you Ricard for your inputs. There is no plastic insulating piece fitted as per photo.

The top contact plate the shaft makes contact with, is permanently grounded so the non insulated shaft tip making contact with it, is no problem electrically.

The shaft should miss the 2 bottom contacts.

There is not much area to fit an insulated piece on the tip of the shaft but if I get the unit running I may later try and fit something.

David
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Old 10th Feb 2020, 11:57 am   #119
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As I referenced much earlier, the Supply Reel Table top spool part (called Upper Clutch Spindle in the 820 manual) has some decomposed material in a grooved ring inside of the normal felt ring. I have not yet checked the Take Up Reel Table but assume that it may well have the same issue

Reading other older posts, says that the material may have originally been cork and is for clutch friction and that people have used various to repair such as drive belts, cable outer insulation/sleeving etc.

Something I am trying work out in my mind is how much protrusion there should be of the clutch friction material, because if the clutch friction protrudes too much from its groove then it will be at a higher level than the felt ring (which is not thick) which I believe is used for back tension.

Of course the best way is to determine by experiment and operational results but would certainly be interested to hear peoples thoughts on this subject.
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Old 10th Feb 2020, 1:02 pm   #120
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Thank you Ricard for your inputs. There is no plastic insulating piece fitted as per photo.

The top contact plate the shaft makes contact with, is permanently grounded so the non insulated shaft tip making contact with it, is no problem electrically.
Reading this, I'm wondering if the plastic piece was not for insulation then, but rather as a bearing, so that the rotating plunger wouldn't over time gnaw a dent or even hole in the contact spring. Plus, in practice, adding a mm or so to the top of the plunger, which is why it's hard to adjust properly now.

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Of course the best way is to determine by experiment and operational results but would certainly be interested to hear peoples thoughts on this subject.
I think the decomposing material was not cork but some sort of plastic such as neoprene. I seem to recall the material crumbling into sticky dark green bits, and I would have thought cork would just crumble.

With the TK819 I once had and played with for a bit I remember just removing the decomposed gunk, and the friction provided by the felt discs together with the torque offered by the solenoids in the reel holders was enough to stop the machine from slipping in fast wind. On the other hand, I do remember that some of the gunk had gotten entwined with the felt, so it could be that the felt had slightly higher friction than originally intended.
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