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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 31st Jul 2020, 2:13 am   #1
martin.m
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Default Grundig TK18L lack of volume

This tape recorder seems to be a cosmetically updated version of the TK18. Tapes would play with clear sound but the volume level was quite low. An attempt at recording produced no sound at all, though the old recording was being erased. The signal from the playback head is amplified by an EF86 pentode followed by an EF83 before going to a conventional ECL86 audio amp and output stage. I decided to check the pre-amp circuitry first as the auto recording level circuit works on the EF83, a variable-mu pentode. There was nothing wrong with the biasing of this valve but both anode and screen voltages were very low, below 10 volts. Same for the preceding EF86. The reason for this was very simple, a 22K resistor that supplies HT to these two valves was open circuit. The circuit reference is R23 and the resistor is roughly in the centre of the circuit board. Once a new component had been fitted the Grundig produced excellent quality sound, both recording and playing back. Not bad for a machine that is nearly 60 years old.
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Old 31st Jul 2020, 10:24 am   #2
DMcMahon
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Default Re: Grundig TK18L lack of volume

I can see R23, good fault finding Martin. Is there an option to do manual recording ? I do not think there is, as it most likely does not have the EM 84 Magic Eye valve.

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Old 1st Aug 2020, 1:15 am   #3
martin.m
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Default Re: Grundig TK18L lack of volume

There is no option to set the recording level manually. As you state correctly, there is no magic eye. However the auto record level works very well and the recording quality is excellent. There is a very good description of how the circuit works in the trader sheet for the TK18 available from this site.
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Old 2nd Aug 2020, 6:02 pm   #4
DMcMahon
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Default Re: Grundig TK18L lack of volume

Yes a good description, good to hear that the automatic recording works well, sometimes automatic recording generally does not receive good press.

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