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RE: Manual or bias info for Luxman SQ-38 sig?

rverdun, hi. It should be the classic way Luxman did their push-pull amps. SQ-38 is EL34. If no bias/balance controls are evident and/or test jacks for metering you probably have to invert the amplifier. Short the inputs and put a load on the outputs. Remove the bottom plate and look for trimmer pots underneath. Usually Lux bias is near the power transformer. This applies to both channels. Looks for 10 Ohm resistors in series with the output tubes' cathodes. You will need a volt meter accurate in the 1.0 Volt range. The bias trimmer pot raises or lowers bias negative voltage. You will want to turn these pots all the way counter clockwise. Now look for the balance trimmer pots - one for each channel. Try to center these before proceeding. These will be in the bias circuit as it feeds the output tube grids. With the amp On attach your V meter across one 10 Ohm resistor. For EL34 I think you will be safe to set the bias level to 0.4 V. You will have to measure voltage across the 10 Ohm resistors, one then the other, until each reads the same. Remember: push-pull amp biasing is like a teeter-totter. The bias sets the height of the fulcrum and the balance makes horizontal (or equal) the teeter board. I'd be happy to walk you through this via the telephone if you wish. This proceedure sounds complicated but once you have gone through it (and maybe take some notes) it should be a piece of cake from there on out, but you must have a good Volt Ohm Meter. Happy Biasing/Balancing and Happy Listening.


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