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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 17th Feb 2020, 9:16 pm   #181
Boulevardier
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Default Re: Grundig TK 819 Any Useful Info

OK, fine. I just wondered if, without tape, the end-of-tape switching would come into play and disconnect the motor and the signal. But obviously not if the hubs were turning.

Mike
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Old 17th Feb 2020, 9:45 pm   #182
DMcMahon
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Default Re: Grundig TK 819 Any Useful Info

Good point Mike, I have not yet looked at EOT operation on the TK 819, I assume it has got EOT (it must have). During my said tests the capstan & spools were running.

David
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Old 17th Feb 2020, 11:44 pm   #183
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Default Re: Grundig TK 819 Any Useful Info

Repeated tape head demagnetiser hum test with tape loaded and running, same results as no tape loaded, i.e. loud hum from relevant PB head, e.g. right head for reverse playback.

Note - with/without tape the resultant hum is louder from the right hand head.

Did the same tests with the head connectors removed from the head assembly to see if could induce hum into the cables without the heads being connected, got zero hum, still get hum of course if head wiring touched at the pins of the connectors.

Probably stated it before but only get hum (during the hum induced tests) when Playback AND Track 1 (Forward Play) / Track 2 (Reverse Play) push buttons are selected, which is correct.

Tested EOT by momentarily (and longer when it did not work) grounding out the appropriate EOT sensor post, the right hand one worked reliably for RWD & Reverse Play, switching off the motor and drive and all tape transport push buttons reset with a loud clunk (ones that were selected).

The left hand EOT sensor post did not work at all, so another thing to add to list of things not working.
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Old 18th Feb 2020, 8:12 pm   #184
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Default Re: Grundig TK 819 Any Useful Info

The first time I saw the fairly large stop solenoid physically pull the stop button down at EOT I was quite startled!
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Old 18th Feb 2020, 9:32 pm   #185
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Default Re: Grundig TK 819 Any Useful Info

Yes it certainly gets ones attention when it occurs
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Old 21st Feb 2020, 7:25 pm   #186
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Default Re: Grundig TK 819 Any Useful Info

Tried checking continuity again from the PB heads to the input of the EF804 Valve (AKA EF86) at C1 capacitor but no joy. With tape playing scope probed C1 and also for good measure the anode output of the valve at C4 but no signal seen.

Also scope probed the heads wiring at the connectors on the heads assembly but nothing seen with tape playing.

Its looking more and more like there is no signal from the PB heads. Will wait until my spare PB/Record head arrives and fit that and try again.

Noticed that the EF804 anode DC voltage seemed high at 200 volts, schematic valve base info indicates 50 volts, this possibly may indicate the valve is not conducting.
Will look at this further once I get a signal at the control grid (C1 input).
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