Mazda triode valve, UU5; a classic Mazda indirectly-heated HT rectifier with a characteristic envelope shape. One side of the heater is connected to the cathode. The anode cavities are each made from two black pressed plates. This rectifier is designed to work into a maximum reservoir capacitor of 8 µF.
The UU4 (350V) and UU5 (500V) were used in larger radios from the mid-1930s and remained in the lists until the 1960s. (National Valve Museum website)
Mazda pentode valve, AC/PEN from the National Valve Museum:
The Mazda AC/Pen, introduced in 1930 on the B5 base, was the first technically successful indirectly-heated power pentode capable of enough output to drive a moving-coil loudspeaker at good volume. The envelope contains a bright cylindrical anode with clearly visible grids. The electrodes are held in, or clamped to, a glass pinch, from which wires will run to the spring base pins. The Mazda AC/Pen...
Mazda triode valve. HL2 from National Valve museum: The HL2 is a general purpose triode but the Mazda advert for this metalised valve suggests that it is well suited for use as a leaky grid detector of first audio voltage amplifier.
Mazda pentode valve SP 41 from National Valve Museum
Mazda pentode valve SP 41 from National Valve Museum: The SP41 is an amplifier pentode with external metalisation as shielding. The original design was from Mazda, and other manufacturers copied this successful design after it had become established. The demand for efficient video pentodes for TV came a year or two earlier in Britain than elsewhere and the SP41 was Mazda's solution. Shorter leads ...