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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 Yesterday, 11:50 am   #81
ms660
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Default Re: Grundig TK 819 Any Useful Info

Yes, there wouldn't have been a transformer fitted for the condenser mic.

R33 is an 8 Watt wire wound resistor, high power because the A relay is powered from the main HT.

Lawrence.
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Old Yesterday, 12:05 pm   #82
DMcMahon
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Default Re: Grundig TK 819 Any Useful Info

Double checked that C2, R4, R6 &, R2 are definitely not fitted/ are missing and am sure these would have been for the DC polarising supply for an old condenser microphone.

The mic transformer is mounted on an insulated board (Paxolin type) and the board is riveted to the metal chassis side panel, so looks like it could have been original build, maybe there was an option then for Condenser mic or other.

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..

Later in the day will plug in a mono jack plug and buzz out (continuity/resistance check)
the jack plug to the jack socket 3 wires then all should become clear. I will not buzz out the microphone jack connections as I have read forum posts that say microphone transformers can be damaged by resistance checks.
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Old Yesterday, 12:07 pm   #83
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Default Re: Grundig TK 819 Any Useful Info

Quote:
Originally Posted by ms660 View Post
Yes, there wouldn't have been a transformer fitted for the condenser mic.

R33 is an 8 Watt wire wound resistor, high power because the A relay is powered from the main HT.

Lawrence.
What is the square wave/thermal symbol against it on the schematic ?
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Old Yesterday, 12:24 pm   #84
ms660
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Default Re: Grundig TK 819 Any Useful Info

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Originally Posted by DMcMahon View Post
Quote:
Originally Posted by ms660 View Post
Yes, there wouldn't have been a transformer fitted for the condenser mic.

R33 is an 8 Watt wire wound resistor, high power because the A relay is powered from the main HT.

Lawrence.
What is the square wave/thermal symbol against it on the schematic ?
It means it's wire wound resistor "druhtwiderstand"

Lawrence.
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Old Yesterday, 2:52 pm   #85
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Default Re: Grundig TK 819 Any Useful Info

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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; Yesterday at 3:17 pm. Reason: word change
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Old Yesterday, 6:44 pm   #86
DMcMahon
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Default Re: Grundig TK 819 Any Useful Info

Quote:
Originally Posted by ms660 View Post
Quote:
Originally Posted by DMcMahon View Post
Quote:
Originally Posted by ms660 View Post
Yes, there wouldn't have been a transformer fitted for the condenser mic.

R33 is an 8 Watt wire wound resistor, high power because the A relay is powered from the main HT.

Lawrence.
What is the square wave/thermal symbol against it on the schematic ?
It means it's wire wound resistor "druhtwiderstand"

Lawrence.
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 Yesterday, 7:08 pm   #87
DMcMahon
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Default Re: Grundig TK 819 Any Useful Info

Quote:
Originally Posted by ms660 View Post
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.
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 Yesterday, 7:11 pm   #88
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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 Yesterday, 11:15 pm   #89
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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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