6AB8

The 6AB8 is a common-cathode triode-pentode, covered by Brimar and Mazda-Belvu together with ECL80. Designed for television scanning, Brimar proposes the triode as frame blocking oscillator and pentode as frame output, also the triode for line timebase or audio voltage amplification and pentode for sync separation or audio output. Performance therefore depends on which section and circuit are considered.

The heater is rated 6.3 V, 0.3 A, with indirect heating. Philips permits AC or DC and the sheets allow any mounting position. Both sections share the cathode, without independent cathode returns. Specimen photographs show the small triode above the pentode; collected descriptions also identify differing supports and connections, not grounds to apply one specimen’s measured dimensions to every production.

Philips, 18 January 1950, specifies pentode audio operation at plate/screen 170 V, grid −6.7 V, suppressor zero. Plate current 15 mA, screen 2.8 mA, plate load 11 kΩ give 1 W output at 10% total harmonic distortion. At plate/screen 200 V: 1.4 W at 10%, plate 17.5 mA, screen 3.3 mA. Mazda-Belvu adds 250 V plate, 17.5 kΩ load, screen fed through 4.7 kΩ, giving 1.55 W at 10%. Power depends on voltage, load and distortion.

For triode audio voltage amplification, Philips specifies 170 V plate supply, 220 kΩ plate resistor, following valve’s grid resistance 680 kΩ: gain 11.5, output 20 V RMS at 5% distortion; at 200 V supply output 24 V RMS. These are loaded-circuit results, distinct from intrinsic amplification factor. Its characteristic table at 100 V plate, −2 V grid gives 4 mA, transconductance 1.35 mA/V, factor 18.

Limits differ by document. Philips registration gives pentode plate 250 V, plate dissipation 3.5 W, screen 0.75 W; Mazda-Belvu and Brimar give plate 400 V, 3.5 W, but screen dissipation 0.75 W Mazda-Belvu, 1.2 W Brimar. Triode limits are 200 V, 1 W. The 550 V zero-current rating is distinct from working limits. Pulse limits also have conditions: Brimar at most 10% of a cycle and 2 ms; Philips associates its values with 15% and 50 µs. Pulse current is not continuous current.

B9A connections: triode plate/grid 1/2, common cathode/internal shield 3, heater 4/5, pentode plate 6, suppressor 7, screen 8, control grid 9. Both sections have maximum 150 V heater-cathode and maximum external resistive connection 20 kΩ between them. The separate suppressor terminal is not a second cathode or spare contact.

Mazda-Belvu gives maximum diameter 22.2 mm, seated height 60.3 mm, pin length separately 7.14 mm. Philips gives maximum diameter 7/8 inch, seated height 2 3/8, overall 2 5/8, bulb length excluding tip 2 ± 3/32 inches. Observations remain distinct by manufacturer and document. Documentation: Philips Data for RMA Registration ECL80, four sheets dated 18 January 1950 collected under 6AB8; Brimar ECL80/6AB8 Replacement Type, pages 178–179; Mazda-Belvu ECL80/6AB8 Triode Pentode, January 1968, seven pages.