Tube Question

I searched in the Tube rolling thread but can’t find what I am looking for. I have switched the tubes in my BHK Pre and BHK 250. I installed 12AX7A/ECC83 in my Pre and 7308/E188CC in the BHK 250. The volume does not seem to work. As I increase the volume it hardly rises until somewhere around 25, and 52. Then a pop and a large volume increase. I obviously didn’t play around with it and shut it off. I didn’t think I needed to change any of the jumpers but maybe I am wrong?

Any help would be appreciated.

Those are two rather-different tube types that are NOT interchangeable… Not only do they use different heater Voltages but they have different pin-outs… I’m suprised either of those work at all.

Put the 'X7s back in the preamp and the 6DJ8/ECC88/7308s back in the poweramp and see if they work.

FWIW, members of the 12A*7 tube family are theoretically interchangeable, but each’s electronic performance is NOT the same so results may be audibly poor.

And I hope you didn’t fry any of your tubes.

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I took the 12AX7A/ECC83 out of the BHK Pre and that fixed the issue. I left the E188CC/7308 in the BHK250. Are you saying that’s not a good idea?

I thought the 12AU7 was interchangeable with the 12AX7

Research carefully before rolling tubes.
12AX7 generate much different gain than do 12AU7, for example.


The amplification factor (mu) of a 12AX7 is 100 while for a 12AU7 it’s 20.

While I had a 250, that was my favorite tube in it. Enjoy!

Thank you ever one for the replies and help.