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Old 27th Nov 2022, 8:42 pm   #14
DMcMahon
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Join Date: Apr 2019
Location: Worthing, West Sussex, UK.
Posts: 6,587
Default Re: Revox A77 doesn't erase

Quote:
Originally Posted by mole42uk View Post

I've checked both the input channels with a suitable signal, the VU meters indicate correctly, there's a believable signal at the collector of the output transistor of the record PCB, but the only signal that gets as far as the record heads is the oscillator.
Note - that the record signal that goes to the record head is much smaller voltage amplitude compared to the record bias signal and of course the bias signal is a much higher frequency. Depending upon your scope settings and how strong the record signal is, it can be very difficult to see the record signal which is effectively modulated onto the bias signal.

You generally have to set the volts per division to a much more sensitive setting (compared to if you were monitoring the bias signal) and set the timebase accordingly for the audio record signal.

On some machines the difference can be dramatic, on some machines I have half convinced myself that the record signal is rubbish/nonexistent (because can be so difficult to see) when in fact the machines record very well.

David
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