McCullough 400
AC Det/Amp Triode
1925

The McCullough tube was the first US indirectly heated triode. Since the 5 pin base had not yet been introduced, the heater connections were brought to the special cap on the top of the tube. A bakelite UV base was used, but an earlier version of this tube had a brass UV base. The tube cartons were marked Type 400, but the tubes themselves were marked McCullough AC.