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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 19th Jan 2020, 11:30 pm   #61
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Default Re: Grundig TK 819 Any Useful Info

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Originally Posted by ms660 View Post
C27, the capacitor connected between the push button contacts 1,1 and 2,1 on the switch wiring diagram and the schematic ?
Thank you Lawrence, but it is not C27, the one in question is on the other side, I cannot easily see it on the components layout drawing..

David
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Old 19th Jan 2020, 11:40 pm   #62
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Default Re: Grundig TK 819 Any Useful Info

Looking physically at the switch it is the "Recording" switch (Aufnahme).
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Old 20th Jan 2020, 12:49 am   #63
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Default Re: Grundig TK 819 Any Useful Info

After some struggling managed to fit the new capacitor, but got a bit confused whether it went on the bottom connection on the switch or the one above, I fitted it to the one above (I think second connection from the bottom).

Slightly concerned that I may have got it wrong !
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Old 20th Jan 2020, 12:58 am   #64
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Default Re: Grundig TK 819 Any Useful Info

Just wondering now if the unidentified capacitor is the previously missing C24 that has gone walk about from where the drawing physically shows it, in the underneath section, will check that possibility out tomorrow.
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Old 20th Jan 2020, 10:53 am   #65
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Default Re: Grundig TK 819 Any Useful Info

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Originally Posted by barretter View Post
I would be a bit wary of those Rifa snubbers - they have a bit of a reputation for spontaneous combustion accompanied by a pervasive pong. I have experienced this a couple of times, granted they were quite old and yours look new. You could make your own with a polypropylene cap of the right value and a much higher voltage and a 100ohm resistor connected in series.
Have been reading loads on Rifa on the forum, there are so many references (old and more recent) that impractical to properly read & digest all of them fully.

Many give bad press but some others good press. I think quite a lot of the bad press are for old (vintage parts) but also there are also reports of more modern parts failing. Much of the bad press is aimed at the X2 Safety capacitors but RC Snubbers are not immune.

Even though obviously there have been issues historically and there may still be some issues, I consider some of the statements are like "Chinese whispers", where someone hears that Rifa are bad and then promulgate that Rifa are bad without little experience of the issues themselves.

I purchased the parts new from RS, I chose RS rather than private sellers as I thought with RS (or similar component distributors) that would get an OEM part with traceable quality standard, rather than risk worse case a cloned inferior part from elsewhere.

When I ordered the parts I did not realise they were Rifa, they are advertised as Kemet. I did not realise at the time that Kemet brought out Evox Rifa many years ago. At the time of ordering if I had realised that they are branded Rifa then I may have decided to look at other options.

I now see on the Kemet datasheet for the part, that the image of the part clearly shows Rifa on one side of the part, I had looked at the data sheet on the RS website at the time but missed that bit of information !

Hopefully I have not made an inadvertent decision, only time will tell.
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Old 20th Jan 2020, 12:04 pm   #66
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Default Re: Grundig TK 819 Any Useful Info

Well, if nothing else, despite their tendency to fail, lots of Rifas have been put into service in a lot of equipment over the years so you'd be in good company.
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Old 20th Jan 2020, 12:29 pm   #67
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Default Re: Grundig TK 819 Any Useful Info

From continuity measurement from the junction of C11/C10 back to one side of the unidentified capacitor at a relay, it does appear that the unidentified capacitor is the missing C24.

So C24 is not physically where the documentation shows it to be but it is electrically correct.

Difficult to follow back the 2 screened cables that connect to the capacitor to be 100% sure but at the moment I am happy that it is C24.

Quote:
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Well, if nothing else, despite their tendency to fail, lots of Rifas have been put into service in a lot of equipment over the years so you'd be in good company.
Hopefully good company with no blown snubbers
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Old 20th Jan 2020, 12:41 pm   #68
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Default Re: Grundig TK 819 Any Useful Info

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Originally Posted by ms660 View Post
Regarding the schematic, the relay contacts that switch the heads are the K relay contacts, but the contacts to the left of C24 (1.12, 2.12 & 3.12) are in the main switch block...12th row...contacts 1, 2 & 3 in the switch layout diagram, contacts 1 & 2 (12th row) connect the output from the rec/playback amplifier to the head when in record and contacts 2 & 3 in the same row connect the output from the rec/playback amplifier to the audio output stage when in playback, pins 5 & 2 on the remote connect the output from the rec/playback amplifier to ground if they are connected together.
Pin 2 at the Remote Control connector was ground (before Remote Connector removed for Bulgin mains connector upgrade) so 5 switching to 2 grounds the same connection point as the AI/AII contact we were discussing, interesting are things come together.
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Old 20th Jan 2020, 12:58 pm   #69
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Default Re: Grundig TK 819 Any Useful Info

Quote:
Originally Posted by DMcMahon View Post
After some struggling managed to fit the new capacitor, but got a bit confused whether it went on the bottom connection on the switch or the one above, I fitted it to the one above (I think second connection from the bottom).

Slightly concerned that I may have got it wrong !
Looks ok so far as I can make out the second one up in the photo is circuit ref 2,12 which would tally up.

Lawrence.
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Old 20th Jan 2020, 1:54 pm   #70
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Default Re: Grundig TK 819 Any Useful Info

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Originally Posted by DMcMahon View Post
Pin 2 at the Remote Control connector was ground (before Remote Connector removed for Bulgin mains connector upgrade) so 5 switching to 2 grounds the same connection point as the AI/AII contact we were discussing, interesting are things come together.
"interesting are things come together" should have read "interesting how things come together".

I am sure there is a Gremlin in my keyboard !
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Old 20th Jan 2020, 1:55 pm   #71
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Default Re: Grundig TK 819 Any Useful Info

Quote:
Originally Posted by ms660 View Post
Looks ok so far as I can make out the second one up in the photo is circuit ref 2,12 which would tally up.
Thank you for checking Lawrence.
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Old 20th Jan 2020, 5:30 pm   #72
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Default Re: Grundig TK 819 Any Useful Info

4 new fuse holders have been fitted.
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Old 20th Jan 2020, 7:31 pm   #73
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Default Re: Grundig TK 819 Any Useful Info

You're doing well now.

Keep at it.

Lawrence.
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Old 20th Jan 2020, 7:42 pm   #74
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Default Re: Grundig TK 819 Any Useful Info

Does anybody recognise the round metal component, it has 2 pairs of small wires coming out of it. I cannot easily see it on the components layout or the electrical schematic.

It looks a little familiar but I cannot drag out of my memory what it might be ?
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Old 20th Jan 2020, 9:54 pm   #75
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Default Re: Grundig TK 819 Any Useful Info

Can't see any connection from the mic jack to a polarizing voltage supply, so could it be a small microphone transformer ?

Lawrence.
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Old 20th Jan 2020, 11:35 pm   #76
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Default Re: Grundig TK 819 Any Useful Info

Hi Lawrence,

I think you may have hit it on the head, I was coming to similar but from a slightly different direction.

I have now completed replacing all the old paper (mainly Frako) capacitors, 7 in total tonight. 2 of them that connected to the ECC 81 were really difficult due to many components going to the valve and surrounding it.

It was proving to be so difficult that I was considering leaving the last 2, but thought better of it and eventually got them replaced, I was pleased I did because one of the two in particular was in a very poor condition, basically falling apart when I disturbed it.

But there was one capacitor I could not locate (I think it is not fitted anywhere) namely C2 a large paper 0.25uF, shown in the components drawing sitting between the microphone and the radio jack sockets.

On the schematic it connects to potential divider R4/R6/R2, I am struggling to locate these also (note that R2 is shown fitted where the transformer is now fitted).

On the schematic they connect back to the 100 volt anode supply of the EF 804, so I assumed that they drop the voltage down to a lower level for an old condenser mic polarising voltage, they finally do connect to the mic jack on the schematic.

So in conclusion it looks like to me that the condenser mic polarising voltage supply components have been removed (will check further in case any of them are hiding) and replaced by the microphone transformer, I have not yet checked where all the wires on the transformer connect to, one does go to the microphone jack.

I know very little about microphone transformers, I must have a read up on them, I assume they are not used with old condenser mics ?

Getting quite close now to powering up, still a little cleaning and tidying up to do, need to refit the Supply Reel table and connect up its electro-magnetic clutch wires etc.

I think I will do the initial power up with just the electrical chassis to make sure nothing obviously untoward.

David
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Old 20th Jan 2020, 11:44 pm   #77
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Default Re: Grundig TK 819 Any Useful Info

Found a small typo in the Service manual. The components drawing that shows the top of the electrical chassis, shows 2 fairly large resistors in the middle behind the motor connector, the left resistor is identified as C33.

C33 is one of the two 40 uF electrolytics, also shown on the drawing close by. The resistor is R33 a 15kohm, looks like some sort of thermal resistor.
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Old 21st Jan 2020, 11:50 am   #78
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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 21st Jan 2020, 12:05 pm   #79
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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 21st Jan 2020, 12:07 pm   #80
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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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