TO tone stack specialists !

[hebaton]

I just picked up a 67 Traynor YBA-3 that looks all original except that it has a 3 sprung cable and the AC output inlet was disconnected.
My hope is to make this a decent, clean, Fender showman like guitar amp. I am assuming something close could be done working on the input and tone stack.
so I would appreciate suggestions as to what to mod what parts and values to use...

I include the schematic I could find. AS far as I can tell the unit corresponds to V2 version.
AS a side show, IF someone would take a moment to briefly explain how Bass and treble expander circuits work and what they achieve at center position...


Thanks !

[mhuss]

The expander circuits are just twin-T bandpass filters between the plate and grid of their respective stages. Because it's a form of negative feedback, they work backwards from a normal 'T', i.e., increasing the expander control resistance to ground creates more of a mild notch at the T frequencies and vice-versa

[hebaton]

The expander circuits are just twin-T bandpass filters between the plate and grid of their respective stages. Because it's a form of negative feedback, they work backwards from a normal 'T', i.e., increasing the expander control resistance to ground creates more of a mild notch at the T frequencies and vice-versa

SO when wide open, it's as they are bypassed ?

[mhuss]

When the control wiper is at ground, the effect is minimized. There is always some fraction of NFB happening at even that setting, but it's no longer a band pass/band reject filter.