I suggest you call the factory service department. They’ll be happy to walk you through it.
There are two sets of jumpers; voltage and bias current for each tube.
The manual has nice color photos and instructions.
I hope this is the issue.
If the preamp has been working fine with 6 volt tubes and all he did was replace 6 volt with 6 volt then it is not likely that jumper settings are the problem. As we don’t know what tubes you took out or their hours or the provenance of the tubes you put back in then it could still be tubes or the board. The BHK is extremely fussy about what tubes you put in and their triode matching. I have had 6 and 12 volt tubes that were fine even in tube DACs and phono stages that wouldn’t work in the BHK especially the 6 volt ones. After over a dozen sets of perfectly good 6 volt tubes were too noisy for me and 93 db speakers I gave up and stick with the 12 volt tubes they were set up with. If this was a new unit from the dealer it is also possible that they fell for the early hype about the Tungsgram tubes like Kevin Deal did and substituted them in place of the Psvane’s. In this case you would hope the jumpers were changed.
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Based on this experience, it appears making certain the jumpers are set for 12V and installing a pair of 12AU7s may well solve the hiss problem.
Great info.
Elk
From reading here for the last four years and owning the BHK pre for almost that long it appears that their is not a whole lot of continuity between different units as some people claim to be able to use just about anything in the way of tubes and others have problems with almost all of tubes being noisy unless extremely tightly matched. Makes it almost critical in trying to help people with the noise problems to know the rest of their gear and it’s gain structure especially if the BHK pre is anywhere in the chain. While I still have mine I moved to the Supratek 6SN7 based preamp a year ago as my “daily driver” and have no noise problems as it has adjustable gain from 0-25 db. Depending on which of the amps I decide to use I just adjust the gain to account for the different input sensitivities.
Very helpful. I have not paid as close attention. 
(I need a blushing face.)
While there is always some unit to unit variability, my hypothesis is it is indeed the gain structure of each system which is at issue - as you suggest.
My experience with a BHK Pre is limited to stock tubes. It is very quiet.
A very frustrating issue for those who have problems. Hearing noise at the listening position is not good.
What speakers and amp are you using with it? I would think it is also possible that all of the units if tested don’t have the same gain which could also exacerbate the tube issue. I suspect that if I still had my 85 db claimed but 82 db tested by JA Vandersteen Treo CT’s noise wouldn’t be an issue at all or virtually non-existent but speakers over 90 db can have issues based on my unit. Now if I knowingly put an amp in the chain with a low (less than 1 volt) input sensitivity then I am asking for trouble.
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Brothers - Thank you for all your help with m
y topic. I genuinely appreciate it. I decided to witch the preamp back to 12v tubes to give it a listen. Of course, nothing is that simple. I watched the PS Audio video on how to change the voltage jumper from 6 to 12 - easy peasy. BUT, no. In my preamp, unlike the one in the video, there is a blue tab resting horizontally, which reduced headroom over the jumper to the point where I cannot remove the jumper to move it into the 12v position. Any suggestions? In the video that blue tab is vertical and does not create a jumper encumbrance. Continuous thanks. - Jim
I typically use a small needle-nose pliers to move jumpers.
Elk hooves are clumsy for the job without tools.
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I know what you mean about big fingers. I was going to do this job with tweezers, but then ran into the blue transistors blocking the jumpers. That is my current problem. Do I simply bend the two transistors up enough to allow me to remove the jumpers?
I would bend the jumper forward just enough to free it. Do not try to bend the blue component. The entire little board may move slightly back and allow it to clear.
Someone managed to move it as they ship with 12v tubes.