Continuing with the ‘Music City’ badged Laney 100w tube head. Google information led me to believe that this amp was a re-badged Laney Supergroup head. Acquiring a schematic for a 1969 Supergroup 100 mk1 it does in fact look to be correct.
The Supergroup schematic shows the output tubes to be EL34s as opposed to the reported KT77s supposedly originally installed in the Music City.
This is a fixed grid bias system & is measuring – 44.80vdc as opposed to the – 54v stated on the schematic for the EL34s. At the moment the tubes are biased way too hot.
The56k resistor r3 sets this voltage from the bias max negative voltage measured at – 63vdc.
To make this amp easier to setup in future I will implement adjustable bias.
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