Bias settings for replacement outputs (SX-1050, SX-1250)

[supergilson]

I was recently told that bias settings for an original output transistor set are not necessarily the best settings for a replacement set.

Determining a better setting is something that goes beyond my skill level.

I have replaced the outputs in my SX-1050 and SX-1250 with the MJ21193/4 on-semi's.

In both, I adjusted to the original spec.


Does anybody on here do differently?

 

[HVHiFI]

I have always adjusted back to factory spec. Every time you do any retransistoring, you should absolutely readjust the bias it more than likely will be off. I also recheck and adjust after several hours of playing since it is possible to drift if caps and transistors are changed.

 

[supergilson]

Well yeah, but I'm asking if that bias value should be different or not for different transistors. It was suggested to me that different transistors have a different optimum bias.

Me, I have no clue! I am deferring to those who know more than I do!

 

[HVHiFI]

Sorry I will be more specific:

If you are using a similar substitute transistor due to obsolescence of the original transistors the idle current should be factory spec.

Others will argue you can raise it due to the quality and durability of newer semiconductors over the originals. As a general rule of thumb the higher you raise the bias, you will create more heat which will shorten component life. Most bias factory spec is a bit low so components last longer, therefore you could go higher but it will shorten the life of the transistor from excess heat.