Switching out Amp Tubes for Fun and Volume Control
(This is a reprint of an article from an older blog of mine)
I like to tinker. So it should be no suprise that now that I have a tube amp I want to do a little testing to see what it is capable of. I emailed Crate to see about the best way to get into the amp and they provided me with the Final Assembly Schematics for the amp, which showed that removing 2 screws allowed the amp assembly to pivot down.
So what you see here is the transformer, the 4 EL84 tubes and the 3 12AX7 tubes. I borrowed a 12AU7 tube from a friend to see what that would do inserted into the V3 position (the leftmost tube in the front row of this picture). Being that the 12AU7 has a substationally lower gain than a 12AX7 it cleared up the clean channel which when it was on 0 volume had a slight low hiss, but since now the power tubes were getting a lot less power from the inverter tube, it was much quieter.I did have to turn the amp up much louder to get the same volume and it started to break up the clean channel at a lower volume then before. But there was abit of fullness that I seemed to lose. Not sure I am ready to make this change. I need to test some more first. My friend also recommended rather than a 12AU7 a 12AT7 which has a gain level somewhere in between the U and the X.
After trying the 12AT7, I was happy with the reduction in volume and increase in volume knob sensitivity. Right now that is what I’m sticking with.
