RE: [Harp-L] 12au7 tubes

["John Balding" <John.Balding@xxxxxxxxx>]

James Supra wrote:
"Will it make a difference what pre amp (12AX7) I replace with one
12AU7?  Meaning, should I put the 12AU7 in the 1st, 2nd or 3rd? or does
it make a difference?"

When Fender wanted to decrease the gain of the 1959 Bassman, they
changed the 1st gain stage preamp tube. That should answer your
question. (Facing the back of the amp, this is the tube on the far
right.) 
The first two tubes are gain stages; the third tube is the phase
inverter. The first two tubes will have the most drastic effect on your
feedback and tone. If the 12AU7 doesn't quite get it done, leave it
there and try a lower-gain tube in the 2nd tube slot as well. Below is a
list of some common preamp tubes and their amplification factors:
12AX7 100
12AT7 70
12AY7 40
12AU7 17

John Balding







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