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Tim · 16th Dec 2004, 1:23 am

Hi Leverman
The other chaps seem to have this one well covered!
If the machine still doesn't work satisfactorily after a good clean the bias may be weak, possibly caused by a low emmission oscillator valve.
Inside are two EL42 valves. One is used for the bias oscillator(supplies the erase and record bias signal) and the other is the audio output valve. If you swap them round and the erase then works the fault is probably down to a faulty valve. Much more likely however is that it is down to those horrible brown Wima capacitors(look just like toffees, and are just about as much usel!)
If you have access to a multimeter (or even better an oscilloscope) the current through the erase head can be checked in the following way:
One of the connections to the erase head is strapped to chassis. Break this link and insert a 100 ohm resistor. Measure the ac voltage across the resistor. There should be about 100 millivolts (0.1 volts). A 'scope is particularly useful here.
If you are confident with a meter and soldering iron etc. and need to delve deeper,drop me a PM with your e-mail address and I will send you a copy of the circuit diagram etc.
Good luck
Tim

16th Dec 2004, 1:23 am	#6
Tim Dekatron Join Date: Jan 2003 Location: Bradford on Avon, Wiltshire, UK. Posts: 3,310	Re: Grundig TK5 Recording Problems Hi Leverman The other chaps seem to have this one well covered! If the machine still doesn't work satisfactorily after a good clean the bias may be weak, possibly caused by a low emmission oscillator valve. Inside are two EL42 valves. One is used for the bias oscillator(supplies the erase and record bias signal) and the other is the audio output valve. If you swap them round and the erase then works the fault is probably down to a faulty valve. Much more likely however is that it is down to those horrible brown Wima capacitors(look just like toffees, and are just about as much usel!) If you have access to a multimeter (or even better an oscilloscope) the current through the erase head can be checked in the following way: One of the connections to the erase head is strapped to chassis. Break this link and insert a 100 ohm resistor. Measure the ac voltage across the resistor. There should be about 100 millivolts (0.1 volts). A 'scope is particularly useful here. If you are confident with a meter and soldering iron etc. and need to delve deeper,drop me a PM with your e-mail address and I will send you a copy of the circuit diagram etc. Good luck Tim __________________ "Nothing is as dangerous as being too modern;one is apt to grow old fashioned quite suddenly."