ST20/C112 Koch Tone Series guitar amplifier "Studiotone" class A ST20/H Koch Tone Series guitar amplifier "Studiotone" class A ST40/C112 Koch Tone Series guitar amplifier "Studiotone XL" class A ST40/H Koch Tone Series guitar amplifier "Studiotone XL" class A CTSE12/C112 Koch Tone Series guitar amplifier "Classictone SE" CTII20/C112 Koch Tone Series guitar amplifier "Classictone II" class A CTII20/H Koch Tone Series guitar amplifier "Classictone II" class A CTII40/C112 Koch Tone Series guitar amplifier "Classictone II" class A CTII40/H Koch Tone Series guitar amplifier "Classictone II" class A CSE6/C112 Koch Tone Series guitar amplifier "Classic SE" TTIII50/H Koch Tone Series guitar amplifier "Twintone III"