As I said earlier, I'll be building this more or less to Stealth specs, with a few changes, well what does that even mean?
Here is a side by side comparison of the Stealth (top) 3rd channel and the regular 5150/6505 (bottom). The key differences have been highlighted and numbered:
1) The stealth has some extra tone shaping in the input stage as part of the first stage plate load. I'd need to sim this in LTSpice to know exactly what is happening, but it looks like a partial plate bypass, which will roll some of the top end of right at the input.
2) The stealth has an additional 1M resistor between the wiper and ground of the gain pot, changing the taper
3) The OG fiddy has a much larger gridstopper. This acts with the Miller capacitance to form an RC lowpass filter. Larger R values push the corner frequency of the filter down to roll off more top end.
4) The Stealth has a smaller coupling cap, rolling off more bass to tighten the amp. I'll be ignoring this
5) The Stealth doesn't use the famous 39k cold clipper found in the SLO, OG fiddy and rectos. It uses 5k, which is still a cold bias, but not super cold clipper. This eliminates some of the buzzy/harsh 5150 tone by not clipping like an absolute bitch.
6) The Stealth uses a bypassed plate resistor to trim some high end. The OG bypasses R16 to a similar effect. They work in different ways, but do the same thing.
7) The Stealth has a larger bass cap in the tonestack for more lows. The Stealth also has a cathode follower before the tonestack, the OG doesn't. It wont' make much difference as the cathode follower isn't being hugely overdriven like in a Marshall circuit.
Many of these things are there to achieve the same goal but in different ways.
The biggest tonal impact by far will be #5.
#1 Probably helps with ice picky tones by scrubbing the very harshest top out of the signal before it propagates into horrible intermodulation distortion hash, so I will certainly try tacking that in once it's built and debugged.
#3 may be the same as #1 in the grand scheme of things. If I keep #1 from the stealth I should also keep it's #3 or it may wind up muffled.
I'll keep #7 and ignore #4 because I'm a slut for low end.
#6 probably doesn't matter either way.
Good space to work in and the pads will take a little bit of abuse while I try a few mods out.
