Hammond B-3/C-3 Tube Set Complete set of tubes for the Hammond AO-28 preamplifier. Used in B-3, C-3, RT-3, A-100 series and D-100 series organs. Set contains 6X4, 12BH7, 12AX7, 12AU7, (2) 6AU6, (2) 6C4 Easy to install.