Tone King Royalist Mk III
Moderators: pompeiisneaks, Colossal
Tone King Royalist Mk III
Anyone been in one? I’m curious about what they are really doing with the era switch
Re: Tone King Royalist Mk III
Gut shot of a PCB will be very difficult to reverse-engineer, at least for me. Based on the years referenced, it's hard to tell what 1967 means. 1964 would basically exclusively reference JTM45s and derivatives thereof, but by the end of 1967 the JTM45 was replaced by the 1987/1986 with transition models like the JTM50 in between. By 1970 you're firmly in JMP territory. So 1967 is a confusing reference, while 1964 and 1970 are pretty clear. If they're only switching values of components in the signal chain while remaining relatively close to the original schematics, the 1964 and 1967 settings would have essentially the same preamps, while the 1970 circuit would have the 33k/500pf tone stack. I doubt they're dipping into filtering changes, so it's possible they're switching to the lead-spec 33k/500pf tone stack on the 1967 setting and lowering the output stage coupling caps to 22nF from 100nF when switching from 1967 to 1970. I'd imagine they'd also be changing the cathode bypass capacitor's value on V1 between the 1967 and 1970 settings, since most amps from 1967 used shared cathodes which would translate to ~1.5k for Rk and would be fully bypassed. Switching from 1967 to 1970 in other words may switch either or both the output section coupling cap values and/or reduce V1's coupling cap value from fully bypassed to the later spec 680nF.
This confusion gets worse if they're changing the filtering of the amp to correspond since Marshalls trended to become bigger and louder over the 60s with power supplies often struggling to keep up. By the end of the 60s, though, Marshalls got tighter again in particular as they increased the sizes for the reservoir and screens filter caps (see: 100w "Black Flag" era amps with effectively 32uF at the reservoir and 16uF at the screens node vs the 1970 Unicord schematic showing 50uf at both the reservoir and screens node). I built an amp that can switch between different filter values at those same 2 nodes and it makes a big difference in how the amp feels, but using it while the amp is powered up is likely pretty hard on the switch viz high voltage DC switching and resultant arcing. I tried to ameliorate this by making the switch short a high resistance voltage reference between the halves of the reservoir and screens caps. But nevertheless, it's still likely not the easiest on the switch. Tone King may have gotten around the issue by using optocouplers and optocouplers would also keep switch noise low. If they are changing the filtering, my understanding is that most Marshalls through 1967 retained the early AKA bass-spec tone stack values of 56k/250pF, so 1967 may just make the amp squishier.
This confusion gets worse if they're changing the filtering of the amp to correspond since Marshalls trended to become bigger and louder over the 60s with power supplies often struggling to keep up. By the end of the 60s, though, Marshalls got tighter again in particular as they increased the sizes for the reservoir and screens filter caps (see: 100w "Black Flag" era amps with effectively 32uF at the reservoir and 16uF at the screens node vs the 1970 Unicord schematic showing 50uf at both the reservoir and screens node). I built an amp that can switch between different filter values at those same 2 nodes and it makes a big difference in how the amp feels, but using it while the amp is powered up is likely pretty hard on the switch viz high voltage DC switching and resultant arcing. I tried to ameliorate this by making the switch short a high resistance voltage reference between the halves of the reservoir and screens caps. But nevertheless, it's still likely not the easiest on the switch. Tone King may have gotten around the issue by using optocouplers and optocouplers would also keep switch noise low. If they are changing the filtering, my understanding is that most Marshalls through 1967 retained the early AKA bass-spec tone stack values of 56k/250pF, so 1967 may just make the amp squishier.