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Old 21st Aug 2013, 9:14 pm   #14
ukcol
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Join Date: May 2003
Location: Harlaxton, Lincolnshire, UK.
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Default Re: Roberts R200- Distorted Output

Those voltages look normal and healthy Josh and the fact that you get no distortion at 4mA suggests there is nothing drastically wrong with the output stage. It may be that this circuit is a bit marginal in its design and tolerances have pushed it over the edge.

You could leave a silicon diode in and set it up for 4mA and then monitor it for a good while, but I suspect the silicon diode will not be conducting.

Another approach may be to add an 8.2k resistor between the battery negative rail and the cathode of the germanium diode; this would give an extra 1mA thought the R21/X3 combination which may be enough to get the output stage current into range.

Colin M
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