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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 May 2020, 9:40 pm   #21
DMcMahon
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Default Re: Saba TK75. Any Thoughts?

I tried more recording tests, this time using pin 3 of the Platte (Phono) DIN input, previously I used pin 1 of the Radio DIN input. The Platte DIN is less sensitive and higher impedance and I got better recording results, but still a little distorted but am sure a resistor attenuator in DIN cable will sort that out.

I scope monitored the input/control grid of the first section of the ECC 81 valve during recording. The wiper of the Input/Recording level control connects to this grid via the record relay. I got the same results as before, but this time I could see on the scope that the Input/Recording level control has no effect on the amplitude of the record signal.

Assuming the Input/Recording level control is actually working and no broken wires/connections then the most likely explanation is that the record relay is not switching the wiper connection through to the grid, the signal can still get to the grid by another route but at a fixed level. I cannot access or even see the Input/Recording level control wiper connection, to try and monitor at the wiper itself.

Getting to the Record relay looks extremely difficult, so thought I would have a go at removing the Input/Recording level control, so I can check it all out properly. Very difficult to see, but it almost looks like there are 2 banks of connections, like a stereo ganged potentiometer which does not make any sense at the moment.

The Input/Recording level control is not keen to come out, there are some very tight cable connections to it that are difficult to see/get to/unsolder. It will be a lot of fun getting it back in and connected up !

I also want to look at the mains on/off switch part of the control, most of the time the mains switch has been permanently made, but very recently that now is getting problematic where difficult to get it switch on sometimes.
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Old 20th May 2020, 9:29 am   #22
DMcMahon
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Default Re: Saba TK75. Any Thoughts?

After a big struggle I got the Input/Recording level Control removed. It is completely shot.

The wiper is totally open circuited from its 1 Mohm track. There are 5 other connections (also an unused switch connection and 2 earth connections) these I am pretty sure are the 2 switches identified on the schematic as "Part of automatic switch". The SPST switch is working but the SPDT switch is not working.

The mains On/Off DPDT switch sometimes works, but mechanically the switch actuation (denoted by the feel/sound) occurs at different rotational angles, i.e. the on/off switch mechanism must be moving as well as not always electrically working .

Wil be impossible to find a compatible replacement. I will take it all apart but am 100% sure that it will not be fixable and will just end up with loads of broken bits.

So I have ordered a standard 1 Mohm Log potentiometer with DPDT mains switch, it will only have a 43mm long shaft so will need to cut relevant length off old shaft and somehow couple the 2 shafts together to get the required length. This then will give me an operational record level and mains on/off switch.

The 2 switches for the automatic operation are much more problematical, I will have to hardwire permanently either with automatic operation disabled or enabled. This will take quite some checking of the cabling connections back to the various relay connections to establish which wire is what, which will not be easy at all.

Big mystery now is what is the SPDT switch contacts I previously found behind the metal cover next to the shaft of the Control ?? There are only 3 switches listed in the part list and it is not any of those ?
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Old 21st May 2020, 9:19 am   #23
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Default Re: Saba TK75. Any Thoughts?

Opened up the Input/Recording level control, took some force to prise it open. The in-operative wiper contact somehow fixes to a Paxoline disk, the disk is split in two. Considered trying to superglue the disk back together but decided the whole control is past being fixable.

Useful seeing the 2 sets of SPDT switch contact as after checking which contact connects to which external connection contact, this will help a lot later when I come to hardwire the switch's wiring, probably will opt for permanent automatic operation (automatic in terms of the tape automatically reversing at end of track 1 when recording, not automatic in terms of the recording level).

Could not fully open the other end of the control but could not see any obvious signs of the mains voltage On/Off switch contacts ?

Have made a start trying to identify the mystery set of contacts, which have 3 screened cables connecting to them. One of the cables (red sleeved) connects to a small pair of contacts on an arm that the pinch roller is mounted to, this pair of contacts make/close when the pinch roller moves to the Play position.

Have not yet been able to identify these pinch roller operation contacts on the schematic, the other side of the contact connects back to a relay but cannot work out which relay it is or its contact number.

Am waiting for a German Service manual (copy) to arrive, hopefully this will help in identifying these contacts, the German schematic I downloaded the other day is not good enough quality to be of help with the contacts.
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Old 21st May 2020, 11:13 am   #24
Paulus.d
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Default Re: Saba TK75. Any Thoughts?

What an interesting machine ...
Regards Paul
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Old 21st May 2020, 11:18 am   #25
ben
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Default Re: Saba TK75. Any Thoughts?

Quote:
Originally Posted by DMcMahon View Post

Have made a start trying to identify the mystery set of contacts, which have 3 screened cables connecting to them. One of the cables (red sleeved) connects to a small pair of contacts on an arm that the pinch roller is mounted to, this pair of contacts make/close when the pinch roller moves to the Play position.
Muting the signal from the heads when not in play? If they're screened, that suggests audio signals.
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Old 21st May 2020, 1:58 pm   #26
DMcMahon
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Default Re: Saba TK75. Any Thoughts?

Thank you Ben, good input. My German Service manual (copy) has just arrived, I am hoping it will help to identify these contacts and others (this unit is absolutely full of contacts, mostly relay contacts).

The manual even though it looks good, has the schematic cut up because of their original large size and is a very busy schematic and many of the connections are in a funny shade of dark red, all in all not easy at all to locate and follow signals. Looks like there are 3 different versions of the schematic depending upon serial number of the unit.

Once I identify the relevant schematics I will scan the A4 pages and reprint as A3 which will make it a little easier to follow the connections.

David
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Old 21st May 2020, 2:03 pm   #27
DMcMahon
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Default Re: Saba TK75. Any Thoughts?

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Originally Posted by Paulus.d View Post
What an interesting machine ...
Regards Paul
Certainly is interesting and challenging.

David
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Old 26th May 2020, 2:42 pm   #28
hillmanie
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Default Re: Saba TK75 Any Thoughts

[QUOTE=DMcMahon;1224550]Several days ago unpacked the Saba that a had arrived a couple of days before.

Unfortunately it has obviously had a bad knock during shipping. The lid was off and the Take Up Reel Table top hub was lying in the box. The right hand metal spigot in the lid (spool retainer I assume) is badly bent and partially has pushed up through the lid.
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Doesn't this sort of thing make you sick? You start out with a lovely looking piece and some appropriately skilled handler does a grand job of trashing it, usually by slinging it into a truck. As tape recorders are inevitably >10kg this 'annoys' the handler - you know the rest. I've had no less than four of them in smithereens, some irredeemably others more or less heavily cosmetically. In two cases I got full compo though. Much is down to the packer. Business sellers usually best but I've also had a few privates whose packing was impeccable.
It's a lottery and I'm keeping fingers crossed for some en route as I write
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Old 26th May 2020, 2:45 pm   #29
hillmanie
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Default Re: Saba TK75. Any Thoughts?

That TK 75 is a real work of art, classy.
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Old 1st Jun 2020, 2:52 pm   #30
DMcMahon
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Default Re: Saba TK75. Any Thoughts?

Agreed !
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