he suggested a different tube because my choice was too much bottom and the wrong kind of bottom (muddy)
I actually have two of his Voodoo V-plex 50 watt MV amps. On the one that I was having modded, Trace had been working with a well known guitar player who wanted the amp tweaked for a little less high's. When he did this, it added a touch more gain, and low end. I was looking for the same thing, so thats where we started.
On my first Voodoo amp, I was getting this by using certain pre amp tubes, and power tubes. Once he did the mod on the second V-plex, my tube selection was too much, causing the low end to get too loose.
What I did like about the new power tubes is, they had a better high end. So I was able to get the thump I wanted by using the TungSol EL34B power tubes, instead of using EL34-LS tubes and this gave me better top end. Win win for me. Got the exact sound I was after, new power tubes are cheaper, and are more reliable, plus the change gave me a touch more gain.