SP62

The Mazda SP62 is a screened high-frequency pentode intended by its manufacturer for the video output stage of mains-powered televisions. Ediswan Sheet 19/1 describes a small metallized bulb, British Octal base and control grid on the top cap. The heater requires precisely 6.3 V and 0.6 A. The document links operating-point selection to how video and sync signals are handled: maximum voltages alone therefore do not describe the tube's full operation.

Maximum plate and screen voltages are both 200 V. Transconductance of 9 mA/V refers to a specific point: 200 V plate, 100 V screen and zero control-grid voltage. Application examples instead use negative grid bias. One setup at about 115 V screen-to-cathode, −1.25 V bias and 2600 Ω plate load gives idle currents of 20 mA plate and 5 mA screen, with 50 Ω total cathode resistance. The table also includes setups with 1000 or 2000 Ω cathode resistance and different currents; these are complete configurations to read by column.

For common DC-restoring circuits, Mazda recommends 115 V screen and plate load around 3000 Ω. It then considers a sync separator fed from a resistor in the video-output cathode, with the CRT shield DC-connected to its plate. In that arrangement the SP62 screen goes directly to the 115 V stabilizer. Supplying the timebase from the same stabilizer makes synchronization independent of mains-voltage variations as described by the manufacturer. This illustrates how supply distribution affects television stability.

Instructions for that circuit include initial bias −1 to −1.25 V, plate load around 4000 Ω and total cathode resistance around 1000 Ω. Under certain conditions greater sync output can be obtained by raising the latter to 2000 Ω, obtaining extra screen voltage through a resistor in series with the stabilizer. Average curves show plate current and transconductance against grid voltage for different screen voltages at 200 V plate. Listed capacitances are 7 pF plate-to-earth, 10 pF grid-to-earth and 0.004 pF plate-to-grid; earth means the other low-potential electrodes and metallizing joined to cathode.

Viewed from the free end of the base: heater on 1 and 8, cathode 2, plate 3, screen grid 4, suppressor 5 and metallizing 6. Pin 7 is omitted; the top cap is the control grid. The external coating therefore has its own terminal, distinct from the cathode connection. Mazda maxima are overall length 95 mm and diameter 32 mm. These are document limits, not dimensions inferred from specimen photographs or transferred to other family designations.

Documentation consulted: Mazda SP62 A.C. Mains H.F. Pentode, Ediswan Radio, Sheet 19/1, data, typical operation, application notes, dimensions, connections and average curves; no edition date visible in the scan.