12DW8

The 12DW8 combines a diode and two dissimilar triodes for successive functions in 12 V hybrid car radios. Philco and Tung-Sol describe a combined second detector, first audio stage and transistor driver: triode 1 is the first audio amplifier, triode 2 the driver. Operation with about 12 V anode supply is its central application feature. The triodes are not a symmetrical pair; their different parameters suit their different assigned tasks.

The heater requires 12.6 V, 0.45 A; Tung-Sol permits AC or DC. Both typical triode points use anode supply 12.6 V, grid voltage 0 V and anode dropping resistor 100 Ω. Triode 1 has transconductance 2.7 mA/V, amplification factor 9.5, anode current 1.9 mA and grid resistor 1.5 MΩ. Triode 2 has respectively 6.5 mA/V, 6.4, 7.5 mA and 1 MΩ. The quoted voltage is the supply voltage with the specified dropping resistor. The diode characteristic average current is 20 mA with 10 V applied, a table operating point separate from dissipation ratings.

Design-maximum limits for both triodes are anode voltage 16 V, maximum positive DC grid voltage 0 V, anode dissipation 0.5 W per section and grid-circuit resistance 1.5 MΩ maximum. The diode also has maximum anode dissipation 0.5 W. DC heater–cathode voltage is limited to 16 V in either polarity for all three sections. The diode characteristic current must not be treated as a universal current rating.

Capacitances are specified without a shield and with external shield number 315 connected to pin 8. Unshielded triode 1 has grid–anode 1.8 pF, input 1.6 pF, output 0.7 pF; triode 2 respectively 3.2, 4.4 and 0.7 pF. Shielded triode-1 input rises to 2.9 pF and output to 1.4 pF; triode 2 has grid–anode 3.5 pF and output 2.1 pF, with input unchanged at 4.4 pF. Maximum diode-anode to triode-1-grid coupling is 0.4 pF. Shield configuration is therefore part of the measurement conditions.

The B9A E9-1 noval base, diagram 9JC, shows from below: 1 anode, 2 grid, 3 cathode of triode 2; 4 and 5 heater; 6 anode and 7 grid of triode 1; 8 common cathode of triode 1 and diode; 9 diode anode. Any mounting position is allowed. Both makers give maximum diameter 7/8 inch (22.225 mm), maximum overall height 2 3/16 inches (55.5625 mm), maximum seated height 1 15/16 inches (49.2125 mm). Philco additionally gives 1 9/16 ±3/32 inches (39.6875 ±2.38125 mm) from the seating plane to the bulb line determined by a ring gauge of 7/16-inch internal diameter, not overall height. Documentation: Philco, 12DW8, Receiving Tube Data Sheet, Tentative, two pages, referring to JETEC release 2285, October 6, 1958; Tung-Sol, 12DW8, Tentative Data, August 1, 1959, two pages.