Date: Mon, 29 Jan 2001 14:45:44 -0600 From: "Steve Gilliland" Subject: Bassman - What happened to my volume? (NHC)
***NO HARP CONTENT***
At our gig Saturday night, I noticed towards the end of the second set that I could no longer hear my harp in the mix. I thought it was because the volume of our guitars was creeping up (as is normal). Fearing feedback problems, I shut down my Bassman RI and switched over to my vocal mic. I just played through the PA the rest of the night.
Yesterday, I discovered that when I plugged in to Normal 1 and used either my JT30 or GB, I could turn the volume up to 12 without any feedback. Prior to this weekend, having swapped out the pre-amp tubes to 12AU7, 12AX7, 12AX7 (right to left from rear), 6.5 to 7 was the limit. Since I still had the original tube that I had swapped out, I took out the 12AU7 and put the 12AX7 back in. With three 12AX7's in place, the upper "feedback-free volume limit" returned to 7. I then re-inserted the SS rectifier which I had replaced with a 5U4GB tube. This didn't seem to change the volume or feedback limit, so I went back to the tube -- better tone. Finally, I pulled out the two power tubes (Fender 5881's) and replaced them with a pair of spare matched 6L6's. Not knowing how to rebias -- or if the power tubes are even an issue -- I just powered up and tried the amp again. The upper feedback-free limit remained at about 7 with seemingly the same volume. I went back to the original power tubes.
The amp seems to be working fine. The tone is as good as ever. I am concerned, however, because when I first got the amp it was in the same configuration that I've now reverted back to and I could barely turn the volume to 2 without massive feedback. Does anyone have an explanation for what's happened? Are my power tubes dying (although my crude testing would seem to countra-indicate that)? Is what I'm describing symptomatic of some fast-approaching catastrophic failure?
I plan to get the amp to a tech within the next couple of weeks, but the closest one that I could find is 2-1/2 hours away and has a major backlog right now. Any input, advice, or similar experience that you can share will be much appreciated. I have a gig this weekend and I'm wondering if I should just leave the Bassman home.
p.s.
Does anyone know a qualified tube amp tech in the southeastern Wisconsin area -- Milwaukee or Chicago perhaps? Someone that is willing to talk face-to-face and does the work themselves? Thanks again for any help. _________________________________________________________________ Get your FREE download of MSN Explorer at http://explorer.msn.com
