PS Audio BHK preamp owners


Hi

This question is aimed at PS Audio BHK preamp owners regarding the tube bias. I understand that the bias is user adjustable by just moving an internal jumper pin (pretty brilliant). The unit ships with 12au7 tubes set at 4 milliamperes. When the jumper pin is moved the bias is increased to 5 milliamperes. I would like to know if anyone has tried this and if so did you like it? Thank you.

Scot
scothurwitz
I played with this jumper setting on some Amperex 7308 tubes and I liked 4ma better than 5ma.  YMMV.  It's an option to try with the 6922 variants, but I believe you need 5 ma for the 12AU7's.  Pretty good preamp, especially for the $$$!
I also believe the change in bias is so that one can use either 12AU7s or the 6DJ8 family of tubes.  I've switched between those two but never tried different settings for the same tube type.

PS Audio has its own forums and you may find more discussion of this there.
Jbrrp

actually, it’s the other way around, PSAudio suggests 4 miiliamps for the 12au7’s that they ship the BHK pre with and 5 milliamperes when you change to the 6 volt tubes. 

My question is, and I wasn’t clear about it when I first posted the question, has anyone tried a 12au7 and increased the bias to 5 milliamperes? I don’t want to just try it if it’s possibly going to hurt the preamp. A gentleman on the PS Audio forum tried a Tungram 7dj8 which is supposedly Bascom’s (the designer and the B in BHK) favorite tube and he set the bias first to 4 milliamperes and then tried the 5 milliamperes setting and stated, and I quote, “I was amazed at how such a small increase of just 1 milliamperes can make such a big improvement”. Now I’m curious but I don’t want to blow the damn thing up to fing out. Thanks.

Scot
I think you should just call PS Audio.  They are happy to answer questions and they've probably gotten this one before.  
Tomcy6

good advice, I wii give them a call on Monday. Thanks. Do you know if they stopped their own forum? I can’t find any recent posts. 

Scot
Scot,  I think their forums are active, but not very active.  Since their amps and preamps have been around a while now there's not a lot of people asking and commenting on them.

I know when they switched over to their new forum format they deleted posts in the old format and deleted a bunch of posts with a lot of information.  I don't know why they did that.
Their forum is extremely active you just have to go to the right place.

https://forum.psaudio.com/
This has been discussed on the BHK preamp thread at PSAudio. I’m quite sure that you are supposed to only use the bias setting that matches the tube type: 12au7 gets 4ma; 6922 family, which also includes the 7 volt types, 5ma. I believe Bascom himself mentioned this.