Posted by Ron on December 20, 2001 at 10:48:07:
In Reply to: Re: A question for bluzharper. posted by Cinciti on December 20, 2001 at 09:29:11:
Good for you! There is one very easy, non-destrcutive, no-brainer modification that you might want to make when you are up to it. This amp comes stock with a 12ax7 pre-amp tube. That tube works great for guitars but you can get a lot of feeback depending on the harp mic you use. You can replace that tube with at 12at7 or 12au7. These are essentially lower gain versions of the 12ax7 and are interchangeable. The 12au7 is the lowest gain of all of them. I put a 12au7 in my Champ and I can stand right next to the thing with the volume on 10 and not get any feedback.
The feedback devil is pretty much in the pre-amp so dropping pre-amp gain can reduce feedback. You can then push the output stage full blast. I have not taken any sound pressure readings (I have the equipment to do it) but I believe that I get more usable volume before feedback when I use the 12au7.
See how much fun you can have with an old-timey amp?
: Thanks Ron you were alot of help. I appreciate that you obviously spent some time on your reply. I think I'll get the amp. Thanks again
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