Voltage Drop (typical)Tube Voltage Drop (estimate)40V
Max C-input Filter CapacitorMax Reservoir Capacitor (C-input filter)8µF
Notes
Indirectly heated cathode — one side of the heater is internally connected to the cathode at pin 3. This provides controlled warm-up, preventing high-voltage surges on filter capacitors that occur with directly-heated rectifiers.
Base type is B4 (European 4-pin, also designated 'Eu A' or 'E'). Not to be confused with the American UX4 base which has different pin spacing.
Maximum reservoir (C-input filter) capacitor is 8 µF. The Osram MU14 datasheet specifies operation with 4 µF input capacitor — verify capacitor compatibility when substituting.
Designed to replace the earlier UU120/500. Manufactured by British Thomson-Houston Co. Ltd. under the Mazda brand.
The Mazda UU5 was one of the first British indirectly heated rectifiers alongside the GEC/Osram MU14 (1933) and Mazda UU4 (1935). The indirectly heated cathode allowed tighter cathode-to-plate spacing than directly-heated types, reducing voltage drop.
Vdrop ≈ 40V estimated from Mazda UU5 datasheet (Vtr=2×500V, Io=120mA → Vo=580V; higher peak voltage class than UU4 so slightly higher drop per pure tube physics). Source: Mazda UU4/UU5 datasheet.
Pin Layout — B4
1Anode 1
2Anode 2
3Heater and Cathode
4Heater
Socket-Compatible Tubes ⚠ Not electrically compatible