BHK Preamp Bias

[browntrout]

What is the effect when increasing the bias in the BHK Preamp from 4 milliamperes to 5 milliamperes?
Thank you.

[browntrout]

I found the answer to my question in the tube rolling section. BHK himself gave the explanation I needed. I am surprised this information is not in the BHK preamp manual.

[Serhan]

It’s there on page 10 below the picture but no effect listed.

[browntrout]

Correct - Thank you Serhan.

[Serhan]

@BHK

The intent of the bias or tube operating switch was to allow for the use of the 12AU7 and the 6922 family of tubes. For the 6922 types, the current was set for 5 mA and for the 12AU7, 4 mA. It would be interesting to see what you think of the sound when set at 5 mA vs. what you observed when set at 4 mA, the factory setting for the 12AU7.

RIP BHK

[gaswong]

I’m currently adjust to 5ma by using 12au7 , improved the dynamic and more solid bass response

[Serhan]

This is interesting. Some people reported lower detail!
What’s the brand of your 12AU7 tubes?

Edit: tested 5mA with 12AU7. System became too harsh for my ears, especially strings. Happily went back to 4mA

[Alexandro]

@Serhan

tested 5mA with 12AU7. System became too harsh for my ears, especially strings.

@Serhan

What’s the brand of your 12AU7 tubes?