12AD5

The 12AD5 is a remote-cutoff RF pentode documented for radio-frequency and intermediate-frequency amplification. The file identifies Rogers Majestic Electronics as sponsor of JETEC release 1862, March 4, 1957; specification pages are dated October 16, 1956 and curves September 28, 1956. These separate documentary dates place the sheet without automatically establishing the valve’s introduction year. The indirect heater requires 12.6 V, 0.1 A.

The maker gives examples with sliding screen voltage through a 40 kΩ series resistor and a 325 Ω cathode resistor. With anode and supply 100 V, at grid −1.4 V anode current is 3.3 mA, screen current 1 mA and transconductance 1.9 mA/V; at −17 V transconductance falls to 19 µA/V. With supply 200 V and the same network, the −3 V point gives anode current 7.2 mA, screen current 2.1 mA, transconductance 2.3 mA/V and anode resistance 1 MΩ. At −34 V transconductance is reduced to 23 µA/V and anode resistance exceeds 10 MΩ. These points illustrate gain control by bias.

A separate table uses fixed screen voltage: anode and screen 100 V, cathode resistor 325 Ω, grid −2.5 V give anode current 6 mA, screen current 1.75 mA, transconductance 2.2 mA/V and anode resistance 0.6 MΩ. Equivalent noise resistance is 6.5 kΩ there; in the earlier 200 V example with screen fed through 40 kΩ it is 7 kΩ. These are noise parameters under specified conditions, not resistors automatically to be added to the circuit. Curves compare current, transconductance, anode resistance and equivalent noise resistance.

Design-center maximums distinguish anode 550 V without current from the normal anode limit 250 V, with dissipation 2 W. The screen permits 550 V without current, 250 V for anode current below 4 mA and 150 V at the 7.2 mA anode-current reference; maximum dissipation is 0.3 W. Maximum cathode current 10 mA, external grid–cathode resistance 3 MΩ and heater–cathode voltage 150 V complete the principal limits. Capacitances are input 5.1 pF, output 8.1 pF, grid–anode at most 0.002 pF and grid–heater at most 0.05 pF.

Noval B9A base, E9-1: 1 screen grid, 2 control grid, 3 cathode with suppressor and internal shield, 4 and 5 heater, 6 anode, 7 and 8 internal connections, 9 no connection. Preserve the distinction between internally connected and unconnected terminals. Any mounting position. Drawing maximums: overall length 2 5/8 inches, 66.675 mm, seated height 2 3/8 inches, 60.325 mm, diameter 7/8 inch, 22.225 mm; bulb height excluding tip 2 ±3/32 inches, 50.8 ±2.38125 mm. Documentation: Rogers Majestic Electronics, 12AD5 Remote Cut-Off R.F. Pentode, from JETEC release 1862, March 4, 1957, eight pages with 1956 specifications and curves.