JBL 6290 Factory Mods

Just been cleaning and testing a late 80's JBL-Urei 6290 Amp. Very stable amp with lots of current. 4 ohm power is double of 8 ohms.

All the 6200's amps in my ownership seem to have their bias set at 500mV. I reduced this amps bias down to 350mV. Nice clean sinewave and no crossover distortion. DC offset on channel A was 0 and channel B it was 0.6mv. Very low. Cleaned fan and board. Fan seems much quieter with a drop of oil

Come across two mods on both sides with makes me wonder if its factory done or by a service centre somewhere in its life. See if you can spot them.

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