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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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10th Jun 2020, 5:25 pm | #41 |
Dekatron
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Re: Grundig TK 27L de luxe Mystery Cable
Thank you Lawrence & Boulevardier, I have heard of this before but had not latched on to the fact that this Bias Choke was the dummy head.
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10th Jun 2020, 5:35 pm | #42 |
Octode
Join Date: Sep 2017
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Re: Grundig TK 27L de luxe Mystery Cable
Actually, I made a gobslip there - so to be self-pedantic, it's the bias (not the erase) signal that would get back into the recording output stage (thus the name "bias trap"). Still enough to badly upset conditions.
Mike |
10th Jun 2020, 5:50 pm | #43 | |
Dekatron
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Re: Grundig TK 27L de luxe Mystery Cable
Quote:
Lawrence. |
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10th Jun 2020, 6:30 pm | #44 | |
Dekatron
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Re: Grundig TK 27L de luxe Mystery Cable
Quote:
Lawrence. |
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10th Jun 2020, 7:56 pm | #45 | |
Hexode
Join Date: Jul 2009
Location: Mablethorpe, Lincolnshire, UK.
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Re: Grundig TK 27L de luxe Mystery Cable
Quote:
However, there is more confusion. I thought one head wire was always white, but a passage from the (later) TK145 service sheet states different combinations of wire colours (red-red, red-white, white-white etc.) This may have changed in the later machines. I've just had a look at my TK46 (3-head) and the record head is green-white, while playback is yellow-white. So I think you may want to set the bias according to the "red" specification. |
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10th Jun 2020, 8:57 pm | #46 |
Dekatron
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Re: Grundig TK 27L de luxe Mystery Cable
Sorry, my confusion, hadn't seen a photo until now.
Lawrence. |
10th Jun 2020, 9:05 pm | #47 | ||
Dekatron
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Re: Grundig TK 27L de luxe Mystery Cable
Quote:
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10th Jun 2020, 9:09 pm | #48 | ||
Dekatron
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Re: Grundig TK 27L de luxe Mystery Cable
Quote:
I have been meaning to get a VTVM probe for a long time. David |
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10th Jun 2020, 9:10 pm | #49 | |||
Dekatron
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Re: Grundig TK 27L de luxe Mystery Cable
Quote:
Lawrence. |
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10th Jun 2020, 9:12 pm | #50 | ||
Dekatron
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Re: Grundig TK 27L de luxe Mystery Cable
Quote:
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10th Jun 2020, 9:22 pm | #51 |
Dekatron
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Re: Grundig TK 27L de luxe Mystery Cable
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10th Jun 2020, 9:36 pm | #52 |
Dekatron
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Re: Grundig TK 27L de luxe Mystery Cable
Cheers Lawrence, you did well to find the VST 24 probe, loads of interesting information in there to read.
David |
11th Jun 2020, 10:41 pm | #53 |
Dekatron
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Re: Grundig TK 27L de luxe Mystery Cable
Have done various mono line recordings using the Radio/Diode and Phono/Platte DIN inputs and get very good playback results through the internal mono amp with plenty of volume, I used unattenuated DIN cable, the Radio input is the more sensitive.
Next to do some stereo recordings and playback into Hi-Fi amp. Have not worked out yet, if stereo recording played back though the mono internal amp is there any way to combine the stereo recordings into the single channel. |
11th Jun 2020, 11:05 pm | #54 | |
Hexode
Join Date: Jul 2009
Location: Mablethorpe, Lincolnshire, UK.
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Re: Grundig TK 27L de luxe Mystery Cable
Quote:
By the way, forgot to say thanks for posting the translation of the bias set-up procedure. Most useful. |
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11th Jun 2020, 11:11 pm | #55 |
Dekatron
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Re: Grundig TK 27L de luxe Mystery Cable
Many thanks for that.
I had read that 'D' was for playback of synchronous mono recordings (as I said before I assume this is Duoplay mode) but did not realise that it also combined the 2 stereo channels, I will try it and also try the synchronous mono playback, to better understand what Duoplay is. David |
4th Nov 2021, 8:12 pm | #56 |
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Re: Grundig TK 27L de luxe Mystery Cable
Thread reopened as requested.
Cheers Mike T
__________________
Invisible airwaves crackle with life or at least they used to Mike T BVWS member. www.cossor.co.uk |
4th Nov 2021, 9:57 pm | #57 |
Dekatron
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Re: Grundig TK 27L de luxe Mystery Cable
Have been meaning to do more tests on this for a long time, but got it out to do some monitoring tests to support the TK 27 Low Audio Thread.
https://www.vintage-radio.net/forum/...d.php?t=185423. During the tests found that fast rewinding is no longer working, it works a fraction if most of the tape is on the Take Up spool, strange as it was working very well the last time it was checked. Two first observations are that the Supply spool brake in the stationary state is not working at all (nothing to do with the fast rewind issue), very similar to the TK 23 https://www.vintage-radio.net/forum/...d.php?t=181533 and secondly that the Supply spool table clutch is very weak. Took apart the Supply Reel table and found that the Lower Clutch Half was not fitted correctly, it has a peg on the underside that should fit into a hole in the chassis to stop it rotating, the peg was not in the hole. Refitted it correctly but it made no difference at all to the rewind issue. With no spool fitted could see that the rubber drive idler wheel was driving the supply spool carrier OK and not that easy to stop it rotating by grabbing hold of the spool carrier, so not a frictions issue between the idler wheel and spool carrier that some similar models can suffer with. Also with a spool full of tape loaded on the supply spool carrier there was no problem in rewind, so looked like a problem is due to extra load/friction when tape taken through the tape path to the take up spool. So inline with the Worn Tape Guide Thread https://www.vintage-radio.net/forum/...d.php?t=184892 I found that the brass Tape Guide on the exit from the heads to the Take Up spool was quite worn where the tape makes contact, so rotated the brass spacer and then was very pleasantly surprised that it made a huge difference to the fast rewind performance with rewinding now working pretty well end to end. More thorough checks still to be done. A second new issue is that the motor makes a loud whine when powered, which goes away during Play or fast winding, also pressing down on the motor shaft makes the whine go away, maybe oiling is required. David |
5th Nov 2021, 12:52 am | #58 |
Dekatron
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Re: Grundig TK 27L de luxe Mystery Cable
While testing Playback found that often there is a loud hum when the tape is Paused, the hum is definitely not on the tape.
When present the hum can be made worse or made to go away by touching various parts of the recorder particularly if both hands touch different areas. Seems strange but must be a logical explanation. David |
5th Nov 2021, 5:51 pm | #59 |
Dekatron
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Re: Grundig TK 27L de luxe Mystery Cable
Found that even when the hum did not appear to be present, i.e. not audible, that the hum would be recorded to tape every time a recording was done (with no record signal present).
Traced the problem to not having refitting the metal screening panel that sits below the PCB, had previously removed the panel to be able to hinge down the PCB for some measurements and forgot to refit it when the PCB was hinged back up. After refitting the panel now all is good. The motor whine has got worse in that it now is present during Play but still goes away in FFD/RWD. David |
5th Nov 2021, 11:28 pm | #60 |
Dekatron
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Re: Grundig TK 27L de luxe Mystery Cable
Added a drop of oil to the top of the motor shaft trying to get oil into the top bearing, made no difference to to the whine. Was going to do the same to lower bearing but more awkward so decided to remove the lower bearing to be able to lubricate it more easily.
Thought the securing screws for the bearing end plate were screwed into the motor metalwork but when I undid the screws a nut fell out, then realised that the screws screwed into free nuts that are located in a recessed slot on the motor metalwork . Trying to get the nut back in place so that can refit the securing screw is nearly impossible due to the location. Only practical way would be to completely remove the motor assembly, but this is extremely difficult. To remove the motor the motor pulley has first to be removed, this is locked to the motor shaft with a torsion spring, difficult to remove the spring and really difficult to refit it. So will try and somehow get the nut back in place rather than trying to remove the motor. |