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04-06-2026, 10:29 AM
Hi Guys
Regarding the TUT3 Custom Special build questions of post-1:
1. The zener in the bias supply has it cathode at ground. The schematic only shows this generically, where the layout shows the specific ground node. No difference.
2. V2 Rk value: Once Rk is below a certain value there is not much change to the gain, but there will be a change to the current through the tube and its harmonic distortion. A wide range of values are useful. The presence of Ck assures that gain is maximised.
1k5 is a much more common value, so it was written on the layout that way out of habit
3. EQ wiring for Bass and Mid controls is a bit different between the schematic and layout, again because the layout wiring is much more common. They are functionally the same, especially considering the EQ is cathode-driven, which tends to make it less effective.
The overall circuit is just one of the many forms of the Fender Bassman head, copied by Marshall, Traynor et al. Whether fitted with "guitar" values or "bass" values for coupling caps or EQ caps, there is a massive amount of bass response, so changing the cap values are more of a nuance to tone and feel. Nuances are important. How they change depends on many other factors, including the instrument used, how the player plays, how hard the amp is driven, the choice of speakers, the music style.
Have fun
Regarding the TUT3 Custom Special build questions of post-1:
1. The zener in the bias supply has it cathode at ground. The schematic only shows this generically, where the layout shows the specific ground node. No difference.
2. V2 Rk value: Once Rk is below a certain value there is not much change to the gain, but there will be a change to the current through the tube and its harmonic distortion. A wide range of values are useful. The presence of Ck assures that gain is maximised.
1k5 is a much more common value, so it was written on the layout that way out of habit
3. EQ wiring for Bass and Mid controls is a bit different between the schematic and layout, again because the layout wiring is much more common. They are functionally the same, especially considering the EQ is cathode-driven, which tends to make it less effective.
The overall circuit is just one of the many forms of the Fender Bassman head, copied by Marshall, Traynor et al. Whether fitted with "guitar" values or "bass" values for coupling caps or EQ caps, there is a massive amount of bass response, so changing the cap values are more of a nuance to tone and feel. Nuances are important. How they change depends on many other factors, including the instrument used, how the player plays, how hard the amp is driven, the choice of speakers, the music style.
Have fun
