Unison Research S6 (old version) auto or fixed bias?

[timpert]

Hello everyone,

I hope someone can shed some light on this. Here's the situation: my brother-in-law (who lives very far from me) has a Unison Research S6. The old version, with all the EL34 tubes in a single, curved row. As he already has this amp for a long time, and he never re-tubed it, I decided to send him a fresh set of matched output tubes as a present. So my question: is the amp auto biased, or does it need bias adjustment? The new version requires some bias adjustment which can be performed by the user using controls and a meter on the front. The old version has no such controls, which is why I think it is auto biased, but I am not sure.

I trust him with simply pulling out the old tubes and putting in the new ones, which is fine with auto-bias. But if it requires adjustment, I'm going to tell him to wait until I come along for proper bias adjustment.

Thanks for any info!

 

[azazello]

In both cases /auto or fixed/ better You can help him to try adjust bias for new, maybe better sounding, how him will like....

 

[timpert]

The amplifier will not be modified by me, the only thing I will do to it is set the bias if required. If the amp is auto biased, I can tell him to replace the tubes himself and enjoy the new sound as there is no adjustment to be made. Otherwise I need to tell him to wait with trying the new tubes until after I have had the opportunity to properly bias the amp with the new tubes.

 

[ArcticBrew]

This reviewer says it is plug and play with no manual biasing necessary.

SoundStage! Network Ultra Audio -- Archived Article

 

[timpert]

Super, that's what I was looking for!

 

[azazello]

The amplifier will not be modified by me, the only thing I will do to it is set the bias if required. If the amp is auto biased, I can tell him to replace the tubes himself and enjoy the new sound as there is no adjustment to be made. Otherwise I need to tell him to wait with trying the new tubes until after I have had the opportunity to properly bias the amp with the new tubes.

The change of 5-10 ma will give you change of quality of sound...

 

[timpert]

That's true, but the amp appears to be auto biased, so a change in bias current will require a different value cathode resistor, which is a modification. That is not part of the plan.

 

[Fruiticus]

Does anybody have a copy of the schematic for this amp, or indeed the instruction manual. I have just a second amp.Generally pleased but would like to get to grips with the design, The RF remote doesn't work either. I suspect it may need pairing but not sure how to do this either