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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 27th Feb 2020, 2:52 pm   #201
Ted Kendall
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Default Re: Grundig TK 819 Any Useful Info

These connectors are as rare as rocking horse dropppings, having been dropped in favour of DINs after this series. One may turn up on auction sites, but then it needs the vendor to realise what it is, so reaming may be the better choice...
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Old 27th Feb 2020, 5:22 pm   #202
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Default Re: Grundig TK 819 Any Useful Info

Quote:
Originally Posted by DMcMahon View Post
Not sure if it makes any difference but pin 5 was not gounded as such, effectively it was floating, I said zero volts but there was a small slightly varying voltage on it.
The screen grid voltage can greatly affect the anode current and thus in this situation the anode voltage.

For screen grid basics see second paragraph of book page 9 here:

https://www.kevinchant.com/uploads/7...ube_manual.pdf

Lawrence.
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Old 27th Feb 2020, 6:07 pm   #203
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Default Re: Grundig TK 819 Any Useful Info

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Originally Posted by DMcMahon View Post
The TK 819 jack plug measures 0.235" / 6mm

I remember now reading several weeks ago (cannot currently find it) in an older posting (I think for one of the Grundig TK 8XX threads) of someone encountering the same issue and fixing it by drilling though the jack sockets with a 1/4" drill ! saying something to the effect that with some 1/4" jack plug manufacturers, the sleeve diameter was smaller than the standard 1/4".

Seems a bit drastic to have to drill though the jack sockets so I will hang fire on that, maybe I can find a source for the < 1/4" jack plugs.
It's good to know that it is possible to ream them, I would be worried about them getting destroyed due to the metal becoming too thin. Still I would think it would destroy the plating (I'm assuming they are nickel plated brass or somesuch) which is a pity.

I once makeshifted a plug by wrapping an long M3 or M4 screw with scotch tape so that the resulting contraption was 6mm in diameter. That at least made contact with the inner part of the socket.

An idea would be to take something like a round standoff with a 6mm outer diameter (such as this one: https://uk.rs-online.com/web/p/round-spacers/1022326/), put some sort of insulation in the bore, such as heat shrink tubing, and screw an M3 screw into the tube. It won't be pretty but could be reasonably functional and wouldn't necessitate carving up the '819.

Or indeed something like this https://uk.rs-online.com/web/p/round-spacers/1418506/ where the flange would stop it getting pushed in to far.
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Old 27th Feb 2020, 6:51 pm   #204
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Default Re: Grundig TK 819 Any Useful Info

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Originally Posted by Ted Kendall View Post
These connectors are as rare as rocking horse dropppings, having been dropped in favour of DINs after this series. One may turn up on auction sites, but then it needs the vendor to realise what it is, so reaming may be the better choice...
Yes a reamer would be more gentle/controlled than a drill, I have a couple somewhere but not sure if they will be large enough.
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Old 27th Feb 2020, 6:53 pm   #205
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Default Re: Grundig TK 819 Any Useful Info

Great book Lawrence thank you.

David
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Old 27th Feb 2020, 6:56 pm   #206
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Default Re: Grundig TK 819 Any Useful Info

I occasionally see old jack plugs/jack plug cables at car boot sales, will have to keep my eyes open and take my calipers to measure any found.
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Old 27th Feb 2020, 9:28 pm   #207
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Default Re: Grundig TK 819 Any Useful Info

Borrowed a 1.2 Mohm resistor (R2) from my TK 5 and fitted it into the TK 819 as a temporary replacement for the open circuited R9 (1.25 Mohms).

Now get more normal voltages at the EF 86 valve, namely 33 volts at pin 5 Screen Grid (G2) and 45 volts at pin 6 (Anode) and the HT voltage at top end of R9 has dropped down from previous 200 volts to 166 volts. The HT voltage the other side of R10 which feeds R9 and R8 (anode resistor) is 199 volts.

Note - TK 819 schematic shows 100 volts at top end of R8, for various reasons I think this is incorrect/not accurate.

So the Screen Grid resistor made a substantial difference to the anode voltage (thankfully).

No obvious visual change to the EF 86 brightness.
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Old 28th Feb 2020, 11:43 am   #208
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Default Re: Grundig TK 819 Any Useful Info

The removed microphone transformer.
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Old 1st Mar 2020, 6:19 pm   #209
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Default Re: Grundig TK 819 Any Useful Info

Attached are photos showing 4 standard size (1/4") jack plugs that will not fit plus the slightly smaller one that does fit.
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Old 1st Mar 2020, 7:08 pm   #210
Ted Kendall
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Default Re: Grundig TK 819 Any Useful Info

You could get some brass jack plugs skimmed, perhaps?
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Old 1st Mar 2020, 9:10 pm   #211
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Default Re: Grundig TK 819 Any Useful Info

From a separate post someone has offered to sell me some brass ones after he turns them down to 6mm.
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Old 11th Mar 2020, 4:57 pm   #212
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Default Re: Grundig TK 819 Any Useful Info

After replacing the open circuit R9 (at Post # 207) on the EF 86 valve and restoring normal anode & grid voltages, tried playing a tape again and was amazed that now get half reasonable playback sound with plenty of volume ! so this is somewhat encouraging

Now need to test recording and also try and get the clutch rubber replacement material work looked at (although may be a waste of time on the Take Up hub as no solenoid wiring).

Also need to get back to the GI/GII contact set operation for the 7.5 ips speed changeover by the centrifugal motor action, previously was struggling to get GI contacts to electrically to make.
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