I recently built a 5E3 tweed Deluxe clone. In the preamp slots, I put in (2) Tung Sol RI 12AX7s. This amp will start to break up around 3 on the volume knobs. While I like the early breakup from the amp, the breakup itself sounds kinda spikey and brittle. Not overly brittle, but it could still use some smoothing out. Any suggestions for tube substitutions in the preamp slots to help the amp's natural overdrive sound more pleasing?