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dpackard 7th October 2020 03:00 PM

Threshold s350e/sa3.9e bias?
Great forum/site here! Owned an sa3 for awhile and loved it. Picked up a nice s350e to convert to sa3.9e. Easy wire swap on secondaries….Where do you probe for adjusting bias? The emitter resistors are obscured by the heatsinks. Any help is greatly appreciated! Drew

Nelson Pass 7th October 2020 06:46 PM

You will need to tap in somewhere to sense current or it will take forever.

Start with the existing bias and turn it up a bit. Then watch the current and
sink temperature. With the cover on, when the tops of the sinks read 50 deg C
and stay there for an hour you should be done.

dpackard 7th October 2020 07:10 PM

OK, Thanks Nelson! I have to say, I truly admire your amps. That SA3 was terrific. It's what made me want the SA3.9E. I got the manual in the purchase, so changing the secondaries on the S350E is going to be a snap.
Hopefully there is going to be an XA30.5 in my future! Regards, Drew

Nelson Pass 7th October 2020 09:27 PM

1 Attachment(s)
And here is the calibration:

dpackard 7th October 2020 11:53 PM

Thanks again Nelson! When I get to it, I'll be shooting for "Crikey Hot" I found an illustration by Zen Mod for reading bias.....It shows pulling the first red wire out of the term strip(going to the output boards/rails), on the power supp board on top of the filter caps, and inserting a .01 ohm/5 watt resister. then read across it. this way 10mv = 1 amp. Sound about right to you?? You ARE the one and only!! Drew

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