I’ve owned both the Stealth and regular 50 watt heads. I sold the stealth and kept the regular 50w. Except for the bias features the stealth didn’t really sound much different to me.
Right now my 50 watt 6L6 head is at Kaplan amp repair getting dual concentric EQ controls for the green/blue channels and bias points and trim pot added.
Exactly.
I bought a 50w 6L6 v2 head (concentric volume and gain pots) and by happenstance ended up with two new 50w Stealth heads at my studio shortly after that. I A/B/C'ed all three amps closely over several days and they really, truly are practically identical. One of the Stealths was just a bit fatter pre-distortion in the low end than the 50w 6L6, and the other was just a bit thinner, with the 50w 6L6 v2 sitting squarely in the middle of both of them. Other than that, the amps were effectively identical. Identical gain levels, identical gain characteristics, identical EQ signature, identical compression, identical everything. On all channels at almost all settings.
The ONLY real consistent difference I could find between the two amps was that on the Blue channel, when the Gain is set all the way down to between 0 and 1, the Stealth is
very slightly more compressed and the 50w 6L6 has
very slightly more extended presency treble. They are identical at all other Gain settings, and I cannot stress enough that the difference was so slight, at a setting almost nobody will probably ever actually use, that I could barely detect it even when A/B'ing in an isolated studio environment.
I am convinced that any real tonal difference between any single 50w 6L6 and 50w Stealth comes down to component manufacturing tolerances. I'd even go so far as to say that the only reason both of these amps are being made at the same time is so people who like the 100w 6L6 or 100w Stealth can be given the option of buying "the same" amp as their preferred 100w counterpart in a 50w package.
So basically, while the original 5153 100w 6L6 and 5153 100w Stealth amps are different, the 50w 6L6 v2 and 50w Stealth amps are not.