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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 16th Aug 2022, 10:58 pm   #21
DMcMahon
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Default Re: Grundig TK 8/3D Check Out

The recordings above were all done at 3 3/4 ips because the TK 5 is only a single speed machine.

So I must do some recordings on the TK 8 at 7 1/2 ips and compare the results with the same music recorded at 3 3/4 ips on the TK 5.

David

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Old 17th Aug 2022, 8:27 am   #22
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Default Re: Grundig TK 8/3D Check Out

Previoulsy while checking HT voltages, found an intermittent problem with the mains ripple voltage at main HT reservoir capacitor C32 (40uF), sometimes it was normal/good and at other times the ripple would increase a lot to around 35 volts peak to peak (plus ripple frequency would increase and waveform become messy plus HT DC voltage would drop somewhat).

Replacing C32 with a new 47uF 450 volt cured the issue.

Monitoring the HT voltages during the record howl problem, they all remain clean and stable.

David
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Old 17th Aug 2022, 11:11 am   #23
Ted Kendall
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Default Re: Grundig TK 8/3D Check Out

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Originally Posted by DMcMahon View Post
Been trying to find a home for the black metal lever that is sitting on top of the Supply spool carrier in the first photo. Pretty sure it somehow must fit onto the tape speed change bracket to the lower left of the spool carrier but so far can not work out how it fits.

Did various music recordings on the TK 8 and also on TK 5. On playback the TK 5 sounds pretty good, the TK 8 sounds a little better but not dramatically better.

David
That's just a blanking plate to cover the open part of the slot not covered by the speed change knob. It clips into the top of the speed change slider. The TK5 and TK8 are to all intents and purposes identical, save for spool capacity, choice of speeds and loudspeaker arrangements. It would be well to check the state of the R/P head - it is rather prone to wear, although I know from personal experience that it can give some useful output when almost through to the windings.
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Old 17th Aug 2022, 1:14 pm   #24
DMcMahon
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Default Re: Grundig TK 8/3D Check Out

Thank you Ted, I can now see the blanking plate fitted in one of the photos in the Service manual but am struggling to get it to clip into the top of the speed change slider.

I have not yet closely looked at the heads condition (plus I am not good at interpreting head wear) but think the TK 5 heads look more worn, will post some photos.

David
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Old 18th Aug 2022, 6:04 pm   #25
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Default Re: Grundig TK 8/3D Check Out

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Checked out some of the valve electrode voltages and found there was no voltage on EM81 defection anode pin 7, this is resistor R32 (200K) connecting to HT1 voltage.

This seems strange as it had looked like the EM81 was working correctly.

David
After fixing the issue above by resoldering the R32 connection with R31, removed the wire connection to pin 7 of the EM 81 and this stopped the EM 81 display responding to the record signal, so this indicates that the R32 bad soldered connection was OK during the original recording tests.

David
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Old 18th Aug 2022, 6:12 pm   #26
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Default Re: Grundig TK 8/3D Check Out

TK 5 and TK 8 Head photos.

David
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Old 18th Aug 2022, 9:30 pm   #27
Ted Kendall
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Default Re: Grundig TK 8/3D Check Out

Erase heads seldom cause trouble. The TK8 R/P head looks pretty fair - some asymmetrical wear but the polepieces are still of full width. Something has been at the TK5 head, I'd say, whether it be a hardened pressure pad wearing it unevenly or a sharp instrument. The RH polepiece is starting to erode, too. A thorough clean would distinguish dirt from damage, and perhaps a gentle re-lap with crocus paper would help.
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Old 19th Aug 2022, 9:19 am   #28
DMcMahon
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Default Re: Grundig TK 8/3D Check Out

Thank you Ted for your head wear/condition analysis.

The felt pressure pad on the TK 5 that presses up against the PB/Record head is a little hard but no worse than the TK 8 pressure pad.

Because the playback sound on the TK 5 sounds pretty good I think at this stage I will not attempt any re-lapping.

David
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Old 19th Aug 2022, 9:36 am   #29
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Default Re: Grundig TK 8/3D Check Out

Re the TK5 head I agree with Ted, an abnormal wear pattern especially on the lower side. Hard to be sure though. The lighting may be exaggerating the extent of the wear. Regardless, it looks like a great candidate for a careful relap to at least remove the ridges.
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Old 19th Aug 2022, 10:22 pm   #30
DMcMahon
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Default Re: Grundig TK 8/3D Check Out

I have never done any head relapping work before so a bit wary of trying it, especailly when it sounds OK to my hearing, i.e. would not want to screw it up with over zealous relapping attempt.

Once I find my crocus paper I may have a go after doing another thorough head clean.

David
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