Threshold S/550e to SA/4e conversion?

[Barry1]

I'd like to try converting the S/550e class A/AB to an SA/4e class A.
My understanding is that it's easy to do. These amps are the same -- just different power supply voltages and bias settings.

I have an operating manual for the S/SA series. I know the values for the inital bias settings for the SA/4e and that's easy to do. I don't know the required secondary output voltage for the transformer or the power supply.

Could someone share:

1) Which secondary taps to use & the desired PS output voltage?
2) Confirm that the bias settings & PS voltages the only differences?

I'm using this as a subwoofer amp and don't think I need all the power I've got. Not sure what the ohm value is for the subs but I'd guess I'd still be ok power wise.

Thanks Barry

 

[Nelson Pass]

1) Which secondary taps to use & the desired PS output voltage?
2) Confirm that the bias settings & PS voltages the only differences?

You are right: the differences you will be dealing with are supply
voltages and bias.

I don't know that you have the same transformers for both, but if not,
you can do is tap the primaries for 220/240V which will take the supply
voltages down to about 1/4 the power and allow twice the bias.

Worst case, new transformer.

 

[Barry1]

Thank you Mr. Pass! You are the one and only!

Kindest Regards, Barry