BHK Preamp… and tube biasing?

Have been entertaining the idea of trying a different flavor of tubes in my BHK preamp (and BHK 250 amp)… but I’m less-than-clear about tube ‘bias-ing’.

Tube retailers highlight that this is an important step, and I see from some YouTube videos that other vendors have bias adjustment routines built into their units to step you through the process. The BHK manual doesn’t cover this topic.

If simply trying a different flavor of the same tube type (e.g. a 12AU7 from a different manufacturer) is this even an issue for the BHKs?

When does biasing apply, and how do I do it?


In the BHK Pre there’s a jumper and only two settings. Try both and see what works for you. Bias here is not what is usually referred to in tube bias settings. In a BHK Pre it’s just a choice between two bias settings. Normally with tubes that don’t have auto bias, you have to adjust to a defined output parameter for new or aging tubes.

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The BHK 250 only accepts 6 or 7 volt tubes and automatically adjust the bias. The BHK preamp has straps for voltage and current that allows you to use 6,7 or 12 volt tubes. According to the manual the 4ma strap is for 12 volt tubes and the 5ma strap is used with the 6,7 volt tubes. Of course you have to select the appropriate voltage strap too. Beyond that it automatically fine tunes for tube changes of the same type.