6DQ6A

The 6DQ6A is a beam power valve designed for television horizontal-deflection amplifiers. General Electric calls it a beam-power pentode and emphasizes high zero-bias anode current at low anode and screen voltages. The indirectly heated cathode uses a 6.3 V, 1.2 A heater; any mounting position is allowed. GE’s December 1956 sheet distinguishes the 12DQ6A and 17DQ6A: identical active systems apart from heater ratings, respectively 12.6 V/0.6 A and 16.8 V/0.45 A, with controlled 11-second warm-up for series strings. GE’s table does not assign that time to 6DQ6A.

Ratings must retain their manufacturer’s system. GE gives design-center limits: DC anode supply including boost 700 V; absolute maximum positive anode peak 6000 V; negative peak 1375 V; anode dissipation 15 W, screen 200 V and 3 W, DC cathode current 140 mA and peak 440 mA. RCA March 1961 and Tung-Sol August 1962 instead give design-maximum values: DC 770 V, positive peak 6000 V, negative peak 1500 V, anode 18 W, screen 220 V and 3.6 W, average cathode current 155 mA and peak 540 mA. These are not operating points to combine. Television conditions specify 525 lines, 30 frames per second and pulses no longer than 15% of a cycle; RCA also limits positive-peak duration to 10 µs.

Typical characteristics also differ. At anode 250 V, screen 150 V and grid −22.5 V, GE gives anode current 75 mA and screen current 2.4 mA; RCA and Tung-Sol give 55 and 1.5 mA. Both sets give transconductance 6600 µmho, or 6.6 mA/V, and approximate anode resistance 20 kΩ. High zero-grid-bias currents are pulsed or instantaneous measurements, not permission for continuous operation without checking limits. GE limits that test to two seconds. Grid-leak bias requires protection when drive disappears, such as an appropriate cathode resistor. Maximum hottest-point bulb temperature is 220 °C.

Mazda-Belvu’s January 1968 sheet documents an audio application: two valves in class B push-pull. Its example uses anodes 375 V, screens 200 V, grids −30 V and input 60 V peak-to-peak; anode-to-anode load 3800–4000 Ω gives 36 W at the voice coil. The table lists anode current 145 mA and screen current 10 mA in the two-valve example, whereas anode dissipation 10 W and screen dissipation 1 W are explicitly per valve. This is a manufacturer’s example, not a universal output rating for one 6DQ6A.

Functional connections are bottom-view octal 6AM: 2 and 7 heater, 4 screen, 5 control grid, 8 cathode and beam plates; anode on the top cap. Construction variants matter: GE marks 1 and 3 no connection and specifies a seven-contact base; RCA and Tung-Sol permit six-contact bases omitting pin 1 as well as 6. Mazda-Belvu instead reserves 1, 3 and 6 as internal connections. Those contacts must not be used as convenient wiring tie points merely from the type designation. Archived photographs also show constructions with a broad central anode flange, a visible detail that does not identify every version.

Dimensions remain manufacturer-specific. GE gives maximum overall length 4 1/4 inches, 107.95 mm; maximum bulb diameter 1 9/16 inches, 39.6875 mm; seated height 3 1/2 ±3/16 inches, 88.9 ±4.7625 mm. RCA gives the same overall length, diameter 1.438–1.562 inches, 36.5252–39.6748 mm, and the same toleranced seated height; Tung-Sol gives maximum seated height 3.688 inches, 93.6752 mm. Mazda-Belvu gives metric maxima 108 mm overall, 93.7 mm seated, diameter 39.7 mm. Documentation: GE ET-T1449, December 1956, four pages; Mazda-Belvu 6DQ6A, January 1968, three pages; Tung-Sol 6DQ6A, three pages with 1962 data and 1956 curves; RCA 6DQ6-A, March 1961, three pages. Editions, rating systems and construction differences remain distinct.