this is really interesting. Where does that leave the Stealth with regard to differences? Just the external bias points? Or is there a clean channel tweak, as well?
I didn't really do much testing with the clean channels but I didn't hear or feel any significant differences between them in the small amount of time I spent on them. I couldn't definitively tell you what the differences are, if there are any. However, for more info about the Green and Blue channels...
To understand the 50w versions, first we need to understand the 100w Stealth and how it compares to the original, non-Stealth 100w 5150 III.
The 100w Stealth has a pretty gained up Green channel that isn't really clean, and here's the reason why... On all versions of the 5150 III, the Green and Blue channels actually use the same circuit, but the Blue channel just increases the gain. I don't mean "they're just like each other," I mean the Green and Blue channels both route through the same exact same singular circuit in the amp. Changing from the Green to Blue channel simply switches over to a new set of EQ controls on the 100w version, and the Gain is boosted by quite a bit. Schematically speaking, it's actually a two channel amp and the "1st" channel is just given a few extra switching options (another tonestack and more Gain). However, the 100w Stealth has a Blue channel with more gain than the non-Stealth 100w 5150 III. How did they do this? They gave the 100w Stealth's Blue channel more gain by modding the amp so that the 100w Stealth's Blue channel also uses the first gain stage of the Red channel. The unfortunate consequence of this mod is that it effects the entire "1st" channel of the amp and all its switchable aspects. So, both the Blue and Green channels (the same circuit) got that extra 1st gain stage of the Red channel, so as a consequence, the Blue channel sounds a lot more gainy, and the Green really starts to break up with the Gain control turned up anywhere over about 8:30.
Now about the 50w amps... the 100w Stealth was actually created in the first place because Eddie liked the 50w's hotter Blue channel as compared to the less gainy 100w Blue channel, and the Resonance knob. So, the 100w Stealth was just really just kind of a quick and dirty hack to bring the original 100w amp up to relative parity with the 50w amp. Hotter Blue channel, and Resonance control.
So where does this leave us? Well, the standard 50w 6L6 is pretty much already a "Stealth" version of the 5150 III. There's really not much they could do to make it "more Stealth." So all they really did, all they really
could do, was add external bias points and give the amp a fancier, cooler looking all-black front panel design with two "Franky" style stripe metal face plates mounted symmetrically instead of just one like on the regular 50w and
call it a "Stealth" model. However, the 50w Stealth does still have a pure Clean sound in the Green channel, like the 50w 6L6, and not the extra gained-up Green channel of the 100w Stealth.
In my testing, I found the two amps are, tonally, effectively the same. I could literally only tell the differences between the 50w Stealth and 50w 6L6 Blue channels with the Blue channel Gain on both amps below 8:30 or 9:00, where the Stealth had ever so slightly less shimmery, Presency-treble on top. The Red channels were identical. Blue channels were identical with the gain set anywhere above 9:00 or so.