Originally Posted by tunghaichuan
Reply With Quote
Update:!:!
So I finally got around to swapping out the tubes in my Peavey Ultra 112 on the weekend so I thought I should post back and answer the question I posed some time ago.
Question: Power Tubes... Can they cause volume (power) loss as they age?
Answer: Absolutely!
I've been pretty busy of late, so I didn't really adopt the scientific approach of swapping each preamp tube individually to see what happened, I just ripped out six old tubes and put in six new ones. I haven't even made up a bias probe yet so I can't actually tell you how 'hot' the new power tubes are running (This amp has fixed bias, and was designed for the tubes I just put in it, but I'll eventually measure the bias and decide if I need to mod the amp for variable bias)
But enough of my excuses...
What came out. 4 12AX7's. Three with no markings, and one with a small sticker that says "China". Two Sovtek 5881's pretending to be 6L6's (see previous discussion in this thread)
What went in. 4 Tung Sol reissue 12AX7's and 2 SED Winged C 6L6GC's (all from TheTubeStore.com)
What happened when I turned it on.....
Leaving all levels as they were when I last played at comfortable volume in my room, the first thing I noticed was how much louder the amp was. Not just "h'mm I think that's a little bit louder than it was last time" louder, more like "Holy Crapdogs, where's that Master volume at!" louder.
The second thing I noticed was an obvious improvement in tone in all three channels. The clean, whilst always "good", now feels more powerful with a definite extension in bass frequencies and even with the dirty old strings on the guitar I was using, it was noticeably more "chimey".
The Crunch channel is where it all happens on the Ultra, and the breakup now sounds more complex and it also gained some additional high and low frequency range. I'm loving this channel!
The Ultra channel is still a massive gain monster and I've only briefly messed with it with the new tubes, but my first impressions were that there is noticeably more bottom end, and when the gain cranked, it's a lot less "fizzy".
I am really pumped to try it out in a rehearsal space so I can crank it up, but at apartment levels it sounds like a whole new amp. In this case phrases like "It sounded like a blanket was lifted from the speakers" really do apply.
The only negative is it seems I've picked up some hum with the new tubes. It's quite low in volume and is independent of input. In fact as soon as you play a note it's inaudible. It gets louder with Master volume, not preamp volume. I'm thinking power tube related? I bought a matched set which I'd assumed would prevent hum from a mismatched pair, but I suppose it could be a PI with mismatched halves too. I think I should try swapping preamp tubes around and see what happens, but I'd love to hear your thoughts. It's totally something I can live with, and it may have even been like this originally, but if I can fix it, I'll try. I've been using weaksauce tubes for so long.......
