Here is some info Steve Fryette sent me regarding some questions I had about the differences Between the two amps and what to expect when comparing them head to head. "The CLX and Ultralead have the same preamps, different power amp designs, not just different tubes.
It's going to come down to personal taste.
Check the serial numbers when auditioning the two amps. Comparison testing these two models can be tricky if there are more then a couple of years between manufacturing dates".
Serial code is as follows:
ULD4D2A0999
UL= Ultralead (will start with CL for the CLX)
D = Month (April)
4 = 2004
D = 117V (E = 230/240V, A = 100V)
2 = EQ option, 1 = No Option ( CLX only: 3 = Reverb, 4 = Reverb+EQ)
A = Ignore
0999 = production number

If they don't have this type of serial code format, they are over 7 years old and not at all representative of current sound.