Switchable Bias?

Hey All,

I have monoblocks each with a switch that allows bias at 10w or 25w class A operation.

Although the 25w setting is sonically superior, the amps run so hot that I’m forced to turn the amps off when they are not in use, and then when I do turn them on, I must deal with metal expansion noise as the amps heat up — takes a good 45 minutes for the noise to stop.

I’ve been toying with setting the amps to the 10w setting and leaving them on — the amps sound fine with this setting for listening to digital radio and Roon (background music for reading, as well as new music discovery).

Question is, am I doing any harm to the amps hot switching the bias when I want to do serious listening?

What does the manual say?

Have you contacted the manufacturer?

The manual only addresses the heat issue, suggesting the lower bias setting if there’s any ventilation restriction, which is not an issue for me.

No. Haven’t contacted the manufacturer. Only recently started contemplating this possible way of o-eating the amps.

If there is a risk of damaging the amp I would expect the manual to state this.

I think switching would be fine. There are tube amps which you can switch between triode and ultralinear operation while powered up, etc.

As an in-between, you could leave the amp in low bias, and when you want to listen power off briefly to switch to high bias.

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I echo some of what Elk says here. Unless your manual explicitly states hot bias switch is safe I wouldn’t do it. But, thermally you aren’t compromising what you are trying to do by briefly powering down your monoblocks for the couple of minutes or so necessary to switch bias. Your amps have plenty of thermal mass to stay warm while you do the switch.
My rule: always stay cautious when doing something like this. The alternative is risking blowing an amp or the speakers it is driving.