Posted by Ron on October 30, 2001 at 09:52:51:
I use a Blackface Fender Champ amplifier with an Astatic JT-30VC (volume control) mic. The Champ, like most guitar amps, comes with a 12AX7 pre-amp tube.
I just read a tip that said if you are using a bullet type mic, you should get better results from the tube amp if you replace the 12AX7 pre-amp tube with a 12AU7 pre-amp tube. I'm no amp tech-weenie but the basics are that the 12AU7 produces less gain and cuts higher frequencies. It therefore produces less feedback and you can push the amp harder for more grit.
I had an old 12AU7 kicking around in an organ amp that I am not using so I put it in the Champ and fired it up. Prior to the tube switch, I could turn the amp up to about 5 or 6 (with the mic volume all the way up) before I got feedback - depending on where this was all set up. After the replacement I could stand next to my Champ, set the volume on 10, turn the mic volume all the way up, and PRESTO - very little to no feedback and AWSOME gritty sound. Take a few steps away and NO feedback!
The amp is not as loud with the 12AU7 but it actually has more usable volume because the feedback is gone. Plus I think it has a better, more gritty sound.
Since I am no amp-weenie, maybe somebody can elaborate on this further. Maybe I have it all screwed up. At any rate, I think the 12AU7 works better for me.
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