biasing for 4 ohm speakers

Thanks for the feedback. I'm new to tube amps and your feedback is very helpful.

The bias point on any tube is a DC value.

The DC voltage drop across the output transformer is not going to change significantly even if the 4 ohm load is on the 8 ohm tap which it isn't in this case. The short answer:

'No.'

Not that my concurrence of anything Al says matters all that much since Al is a EE and undisputed A'gon techie. By contrast, I am not a techie, just a techie "wanna-be." But what Al says is consistent with my anecdotal experiences. I own an ARC tube amp with output trannies, and as Al said, the output tranny matches the speaker load impedance to optimally load the back impedance presented to the power tubes.

Of course, the moving target variable is that speaker impedance usually varies as a function of frequency response ... and some speaker impedances vary quite a bit. The practical result is that most folks just use the tap that subjectively sounds the best.

If you want to learn more about matching traditional tube amps with speakers, there's a number of threads that delve more deeply into the topic. I personally find it very interesting.

As to your specific question about biasing the tubes, I would be surprised that Jolida would instruct you to change tube bias to compensate for speaker load. At least that is my experience with my ARC amp. But ... as I said, I am not a techie. Call Jolida to be certain.

I'm not familiar with the specific amp, but I would assume that the answer is "no." Presumably the output transformer is designed such that the output tubes see essentially the same load when a 4 ohm speaker is connected to the 4 ohm tap as when an 8 ohm speaker is connected to the 8 ohm tap. Also, the bias current is DC, which won't be affected by what is on the secondary (output) side of the transformer since transformers can't pass DC between their two windings.

Regards,
-- Al