Hello Mates -
Recently I bought a BHK Pre and BHK 250 combo. Now want to roll the tubes of pre and found a NOS GE 12BH7 in my local old tube shop.
The person told me, I can use 12BH7 instead of 12AU7 in my BHK pre. Now, I need your expert suggestion should I use it? Any one as any previous experience?
Thanks in Advance!
Theoretically it should work if the BHK is capable of handling the additional heater current draw. I feel pretty certain that back when BHK was actively participating in the forum he answered this same question so you probably need to do a search. But you might also take into consideration that his personal unit while using the same circuit design may have been built with different tolerance parts than the production units as that’s how things go when the “bean counters” get involved. Another consideration is that if that pair of “found” tubes don’t have almost perfectly matched triodes for the pair you are going to get increased noise especially when changing volume levels. I have owned many tube preamplifiers over the years and the BHK was the most picky about the quaility of tubes of any I ever encountered. So even if the tubes work in general they may not “work” for you in actual use. Plus if the increased heater draw is at the limit for the unit it may work for a while and then cause you to have to buy a replacement board. Bottom line try it at your own risk.
Additional to the above, you may discuss your query with PSA staff.
Thanks dawkinsj and Job_Jalink for sharing your thoughts.
@Paul or any expert from PSAudio - Please suggest.
I don’t know that tube per se (preferring to stick with the stock tube) but it will work.
BHK preamp has the ability to switch heater currents via a jumper inside the preamp. You can go from the standard of 4ma to 5ma. If you can find out the appropriate current the tube wants, use this jumper to set it. From the little reading I did it looks to be the same.
You can also change from a 12v heater based tube to a 6v heater based tube via jumpers too when you’re rolling but the tube you mentioned is a 12v heater. In the end, you’re not going to damage anything if your tube wants more current it just won’t work as well. Go for it!
I have attached the owner’s manual for you,
BHK-Preamplifier-Owners-Manual-Rev-A-V1.pdf (3.8 MB)
Thanks a lot @Paul! You are a life saver.
I’ll try and update the forum.
I would suggest you read through this thread starting at post #277
No link.
FYI.
Here you go.
I have successfully able to use GE 12BH7A tubes in my BHK pre after following @Paul suggestions. It working in both 4mA and 5mA jumber positions. But sound is more engaging when pur the jumper at 5mA. My experience with 12bh7a is wonderful. It turns my BHK pre to a new unit in better way.