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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 21st Jan 2020, 12:24 pm   #81
ms660
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Default Re: Grundig TK 819 Any Useful Info

It means it's wire wound resistor "druhtwiderstand"

Lawrence.
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Old 21st Jan 2020, 2:52 pm   #82
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Default Re: Grundig TK 819 Any Useful Info

Quote:
Originally Posted by DMcMahon View Post
There are 2 pairs of wires coming out of the transformer, one wire of one pair goes to the metal body of the transformer case and from there a black wire connects to earth, the other wire of that pair goes to the normally earthy side (but not earthed in this case) of the mic jack socket.

The first wire of the second pair goes to one of the 3 wires on the mic jack socket and the second wires goes to one of the 3 wires on the radio jack socket.

Bit confused why these mono jack sockets have 3 wires as well as an earth connection, the symbol in the schematic for these jack sockets does not help my confusion..
The transformer looks to be connected as isolating, could be 1:1 or step up.

The jack switches.....looking at the schematic and your photo their contacts appear to open when a jack plug is inserted, prevents the two signal sources from being connected together, isolates the radio input resistor from the polarizing voltage output when a mic jack plug is inserted and keeps DC from the polarizing circuit off the radio line when a radio jack plug is inserted.

Lawrence.

Last edited by ms660; 21st Jan 2020 at 3:17 pm. Reason: word change
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Old 21st Jan 2020, 6:44 pm   #83
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Default Re: Grundig TK 819 Any Useful Info

Quote:
Originally Posted by ms660 View Post
It means it's wire wound resistor "druhtwiderstand"
Thank you Lawrence. I knew from seeing the resistor that it looked like an enamelled wire wound and from the parts list knew it was a wire wound (after translating "druhtwiderstand" of course).

But I did not associate the square wave/pulse train symbol with being a wire wound resistor, it makes some sense though.

I thought I might have seen similar a very long time ago for temperature sensitive resistors/early thermistors etc.
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Old 21st Jan 2020, 7:08 pm   #84
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Default Re: Grundig TK 819 Any Useful Info

Quote:
Originally Posted by ms660 View Post
The transformer looks to be connected as isolating, could be 1:1 or step up.

The jack switches.....looking at the schematic and your photo their contacts appear to open when a jack plug is inserted, prevents the two signal sources from being connected together, isolates the radio input resistor from the polarizing voltage output when a mic jack plug is inserted and keeps DC from the polarizing circuit off the radio line when a radio jack plug is inserted.
Thank you for the good analysis, it makes a lot of sense now. I still later will check it out further with a Jack plug fitted for my own peace of mind.

One thing that helped to confuse me at the time was when replacing the capacitors is that C49 connects to one contact of the Platte jack socket (phono/turntable/gram), this connection had a small thin solder bridge across to an empty connection on the jack socket.

It almost looked like it was an unintentional solder splash that had bridged the 2 contacts, but I think I may be able to see the link on the schematic ?
but I wondered why that jack socket only had 2 wires (ignoring the solder bridge) whereas the others have 3 wires. I think it is because the microphone and radio have a shared input into the EF 804.
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Old 21st Jan 2020, 7:11 pm   #85
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Default Re: Grundig TK 819 Any Useful Info

In the early stages of powering up the electrical chassis. Doing it 1 fuse at a time and checking everything. Now have some valve heaters lit up, slow progress but getting there !
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Old 21st Jan 2020, 11:15 pm   #86
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Default Re: Grundig TK 819 Any Useful Info

After watching a > 2 hour recorded documentary on the Rolling Stones returned to do a little more testing. Plugged in remaining 2 valves (the EM 71 Magic Eye that had previously been removed for its own protection as was vulnerable to being knocked) and the ECC 81 (previously removed for snubber tar cleanup).

They like the other valves lit up OK, switched on and off a few times do a couple of checks, each time the valves went off when the on/off switch was switched off.

But a little later on a subsequent switch off, I noticed that the valves this time stayed lit.

Upon investigation both switch poles of the on/off are now permanently switched/made whether the switch is mechanically on or off, the switch makes a lovely solid mechanical sound when switched off/on but electrically now never switches off.

I did not believe it initially and unsoldered the switch wires to double check everything, which confirmed that the 2 mains switch poles are permanently made/shorted.

The switch had been thoroughly checked both resistance and voltage wise during the Bulgin mains plug upgrade and also rechecked all OK at the beginning of the power on tests tonight, but obviously after a short usage has now failed.

Little can do about it, the rear cover of the mains switch (integral to the volume control) is riveted on and even if I drilled the tiny rivets out, not sure if could get inside as the 4 switch contacts protrude through the body and even if could get inside probably unlikely to be repairable.

A shame, I just have to remember now to unplug the mains plug before doing any work inside (of course I would always do that anyway)
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Old 22nd Jan 2020, 1:59 pm   #87
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Default Re: Grundig TK 819 Any Useful Info

Electronics chassis all fused up and powered up, looks OK so far, no bangs, smoke or fireworks. Snubbers OK but of course no inductive motor load yet as transport chassis not fitted yet.

24 vdc supply good at 31 volts 30mV 100Hz mains ripple off load, dropping down to around 26 volts (not a regulated voltage) on relay load.

Main DC HT supply good at 262 volts with 30mV 100Hz ripple (seems very low for HT ripple).

Been checking the various DC voltages to the valves and there appears to a problem with the ECC 81 not seeing any anode voltages, am struggling to find resistor R40 (5kohm) that feeds the main HT to the second anode etc,

This is the valve that I had a lot of trouble with when replacing 2 paper capacitors due to birds nest of components/wires around the valve, so checking it out further to see if anything has been disturbed incorrectly and where R40 has got to.

Magic Eye valve EM 71 lighting up, a bit dim maybe but probably normal.
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Old 22nd Jan 2020, 6:46 pm   #88
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Default Re: Grundig TK 819 Any Useful Info

Just for my own interest, I stripped down one of the old snubbers, the one where the outer insulated case was badly cracked and basically fell apart when snubber was removed.

Unpeeled loads of paper/foil (the capacitor section) to reveal the 100 ohm resistor inside.
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Old 22nd Jan 2020, 11:46 pm   #89
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Default Re: Grundig TK 819 Any Useful Info

After some chasing my tail, found R40 and associated R19 were physically on the other side of the chassis, nowhere near the ECC 81 valve. Found missing anode 2 voltage on the ECC 81 was due to broken wire at the valve pin (this wire connects back to R19).

Wire probably got broken yesterday during very awkward capacitor replacements at the ECC 81.

Even though I have tried to thoroughly clean the snubber leakage sticky tar like material from the ECC 81 valve base socket pins, found that each time valve is removed that the valve pins come out coated with tar, so have been replacing/removing the valve several times, each time cleaning the valve pins, slowly it is improving.

Plan to drill hole in rear of chassis to fit a double pole on/off toggle mains switch and wire accordingly.

Will go quiet for a few days as going to visit family.
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Last edited by DMcMahon; 22nd Jan 2020 at 11:49 pm. Reason: Update
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Old 23rd Jan 2020, 3:17 pm   #90
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Default Re: Grundig TK 819 Any Useful Info

Drill a very small hole carefully in the mains switch phenolic body and apply Servisol whilst working the switch. Unless some part is broken, this usually works.

Leon.
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Old 23rd Jan 2020, 7:33 pm   #91
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Default Re: Grundig TK 819 Any Useful Info

Thank you Leon, sounds a very good suggestion, will certainly try it on my return. I really hope it does work as would be good to retain the functionality of the original switch.

David
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Old 24th Jan 2020, 9:45 am   #92
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Default Re: Grundig TK 819 Any Useful Info

If you want to access the chassis I believe the deck complete can be removed with a multi way plug and a few screws. I had a similar one but decided not to pursue it as the rubber bits were bad, 2 heads missing, the others worn plus all the minor component problems. I tried to give it away foc but not a glimmer of interest and I scrapped it I'm afraid, so I'd have a good think about how much effort you want to put into this. It's a fantastic machine and unbelievably well made however
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Old 24th Jan 2020, 11:11 am   #93
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Default Re: Grundig TK 819 Any Useful Info

Thank you, I already have the Transport chassis separated from the Electrical chassis, this is a really good serviceability feature of the 819 and I assume similar models 820/823/919/920.

The heads are intact and the pinch wheel rubber looks OK, so am hoping next week when I re-assemble it that I may get some playback life out of it. The pressure roller rubbers are very poor condition so they may well require some sort of inventive DIY fix.
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Old 25th Jan 2020, 6:50 pm   #94
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Default Re: Grundig TK 819 Any Useful Info

Let me know if you need a magic eye as I kept that, I have no idea if it's any good but you are welcome to it
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Old 26th Jan 2020, 10:27 am   #95
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Default Re: Grundig TK 819 Any Useful Info

Many thanks, I certainly will. Hopefully I will be checking it out early next week when I see what recording is like.
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Old 27th Jan 2020, 11:54 pm   #96
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Default Re: Grundig TK 819 Any Useful Info

Just for my own interest, tonight I did a DC voltage pass through test of all the removed/replaced paper capacitors, 16 in total (mainly Frako and a few Wilma).

Previously had measured their capacitance and nearly all were close to double their stated values, a couple were well over double. None of them measured low resistance on a DC resistance check (no resistance measurable actually).

Did a fairy low voltage test at 135 volts (tapped off a Grundig TK 5 I am in early stages of looking at) off load test.

All the capacitors passed DC voltage, best couple around 15 volts, most passed 80-120 volts and 2 I think passed the whole voltage, quite surprised how bad they were, now of course consigned to the dustbin.

Same test on new capacitors give as good as zero volts pass through.
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Old 28th Jan 2020, 9:00 am   #97
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Default Re: Grundig TK 819 Any Useful Info

In all honesty though, you're creating a voltage divider with the input resistance of the multimeter as the lower leg and the capacitor as the upper leg. Thus the actual voltage you get is very dependent on the input impedance of the multimeter in question, say 10 megaohms. Of course, it is good as a go/nogo test, and is certainly realistic in terms of what the grid impedance of a valve would be, but the actual value doesn't really say that much without knowing what the actual input impedance of the multimeter actually is.
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Old 28th Jan 2020, 10:34 am   #98
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Default Re: Grundig TK 819 Any Useful Info

Hi Ricard,

DVM used is 10 Mohms input impedance. As I said it was purely for my own interest to see how much they would pass/what sort of leakage they had. They had all been replaced with new Poly caps, so were going to be thrown away anyway, regardless of the results.

David
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Old 28th Jan 2020, 6:27 pm   #99
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Very carefully manually drilled a small hole in the back of the mains on/off switch. First double checked that the switch operation was the same as before, i.e. both switch poles permanently made and mechanical operation feeling/sounding good/normal.

Low and behold, after drilling the hole the switch then worked normally, mechanically and electrically (both resistance and voltage wise).

Tried it numerous times and it was 100% good/repeatable.

For good measure sprayed a little Supersolve Super 10 into the hole (this was the original plan anyway) and operated the switch a few times, but now the switch never switches on electrically ! and mechanically you can feel/hear that it is not now switching on when turned to the On position.

May not have been the Supersolve that killed it, maybe was just the extra on/off operations. Will keep exercising it, in case it comes back to life but pretty sure it is now dead.

I have a toggle switch ready to install, if the switch does not recover.
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Old 28th Jan 2020, 7:59 pm   #100
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Default Re: Grundig TK 819 Any Useful Info

Would be sensible to allow the contact cleaner a while to evaporate before giving up on it...
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