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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 7th Aug 2017, 7:10 pm   #1
richieyork
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Default Grundig TK145 DeLuxe - very quiet

Hi all
Bought an immaculate TK145 DeLuxe at my local car boot at the weekend.
It powers up and the belts seem good!!
However, the volume is incredibly low - at full volume the output from a known good tape is barely audible though seems clear sounding.The 'strip' magic eye isn't glowing at all.
I'm unfamiliar with these machines. I've lifted the lid and base and all 'seems' present and correct though no sign of a physical mains transformer though it seems HT is derived from the motor windings??
Where is the full-wave rectifier - i cant see it anywhere!!!!!
Voltage checks are next up but wondering if you guys know of any stock faults that give this symptom before i wade in deeply.
Many thanks
Richard
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Old 7th Aug 2017, 7:31 pm   #2
TonyDuell
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Default Re: Grundig TK145 DeLuxe - very quiet

The circuit diagram I have for this machine suggests that the motor is also the mains transformer. It has 4 windings, 2 primaries (series or parallel connected for different mains voltages), a 6.3V heater winding and an HT winding.

The HT rectifier, is I think, a contact-cooled selenium rectifier. It's a flat thing, thin aluminium case, screwed to the chassis with 2 tags at each end.

My guess (and it sounds like you're guessing that too) is that the HT line is low due to this rectifier having failed.
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Old 7th Aug 2017, 8:01 pm   #3
richieyork
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Default Re: Grundig TK145 DeLuxe - very quiet

Quote:
The HT rectifier, is I think, a contact-cooled selenium rectifier. It's a flat thing, thin aluminium case, screwed to the chassis with 2 tags at each end.

My guess (and it sounds like you're guessing that too) is that the HT line is low due to this rectifier having failed.
Thanks Tony, found the rectifier. It's and encapsulated oblong block mounted at the top of the chassis and it's giving 244v/248v DC on the nearby HT smoothing cap so it's not short of volts - measured on my DMM - yet it's giving all the symptoms of low HT in that there is no discernible hum on the LS and the magic eye is totally dead tho filament is lit up....

Cheers
Richard
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Old 7th Aug 2017, 8:16 pm   #4
TonyDuell
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Default Re: Grundig TK145 DeLuxe - very quiet

Argh! The diagram I have is for the TK145 De Luxe which seems to use a level meter, not a magic eye, But it may be similar in other respects. It says the HT voltage at the output of the rectifier is around 228V, so yours is a litle high. Maybe due to low HT current drain.

Does your machine have an ECL86 output valve? If so, what voltages do you get on :

Pentode anode (pin 6, 210V)
Screen (pin 3, a bit under 220V)
Pentode cathode (pin 7, 6.6V)

I have given the voltages from the diagram I have, which should be similar.
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Old 7th Aug 2017, 9:06 pm   #5
richieyork
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Default Re: Grundig TK145 DeLuxe - very quiet

Quote:
Does your machine have an ECL86 output valve? If so, what voltages do you get on :

Pentode anode (pin 6, 210V)
Screen (pin 3, a bit under 220V)
Pentode cathode (pin 7, 6.6V)
Hi Tony
OK, a little progress (given i'm unfamiliar with this machine):
The strip magic eye bursts into life when I press down on the record button, so we have HT and the eye works - it's bright, possibly suggesting a low hours machine?
Voltage on the pins of the audio output transformer are showing 233 & 248v. Cathode is giving 7.7v.
Thinking perhaps the ECL86 maybe have gone super low emission I swapped it for an unknown quality used one from my biscuit tin - that was hopeless, it seemed to turn the output amp into a low frequency audio oscillator, albeit not very loud that changed pitch as I turned the volume control!!! Put the original valve back in and we're back to very very low volume as before...

Last edited by richieyork; 7th Aug 2017 at 9:19 pm.
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Old 7th Aug 2017, 9:50 pm   #6
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Default Re: Grundig TK145 DeLuxe - very quiet

The magic eye fitted in this machine is of the later type (EM84 or EM87) and they do not usually seem to lose their brightness like the earlier EM34, EM80/81 etc. A better indication of wear is whether "flats" have appeared on the face of the heads and the general cleanliness of the sound channel (the tape path area surrounding the heads).
You have better boot sales than the ones in my area!
You may have a weak ECL86 (or one of the other signal valves: EF86, EF83 or ECC81 I believe) and/or out of spec capacitors, the machine is nearly 50 years old.
Best of luck with it.
Peter
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Old 8th Aug 2017, 11:21 am   #7
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Default Re: Grundig TK145 DeLuxe - very quiet

Hi
Odd you have a magic eye - like Tony I thought this model used a level meter.
I'd have a quick check on the speaker and socket as corrosion on the latter can cause this. There's not a lot to the output stage so I'm sure you'll soon have it sorted. I like these machines - really quiet runners and above average sound.
Glyn
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Old 8th Aug 2017, 11:57 am   #8
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Default Re: Grundig TK145 DeLuxe - very quiet

I also Have a TK145 I bought it new (pocket money from working down the chip shop) must have been the late 60's mine also has a Magic Eye.

These seem to suffer (well mine has) with damage to the pcb giving all sorts of odd faults.

I should dig it out last seen 20 years ago

Cheers

Mike T
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Old 8th Aug 2017, 5:29 pm   #9
BillDWVA
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Default Re: Grundig TK145 DeLuxe - very quiet

Just a quick thought (that may be confirmed by studying the circuit diagram); does the 'magic eye' only operate when the machine is in 'record' mode? I am sure this was the case when I last had a valve Grundig in bits...
Bill
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Old 8th Aug 2017, 6:18 pm   #10
richieyork
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Default Re: Grundig TK145 DeLuxe - very quiet

Hi Bill
Yes, I finally worked that out :<) It's glowing nicely in 'record mode' and the voltmeter and the nice little shock it gave me last night confirmed we have sufficient HT.
There's something wrong with the output stage however... think the PCB will have to come out and i'll do some component checks without risking another 'belt' off the thing!
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