6AN4

The 6AN4 is a high-mu miniature triode intended by Sylvania and Tung-Sol for grounded-grid amplification or mixing in UHF television applications. It has an indirectly heated cathode, T-5½ envelope and seven-contact miniature base. Its documented role is therefore in high-frequency stages: the 4 W maximum plate dissipation is not an audio output rating. The consulted sources do not specify a universal maximum frequency for the type.

The nominal heater requires 6.3 V and 0.225 A, AC or DC. For class A1, Sylvania and Tung-Sol give plate voltage 200 V, cathode-bias resistor 100 Ω, plate current 13 mA, transconductance 10 mA/V and amplification factor 70. The approximate −7 V grid voltage instead applies when plate current is reduced to 20 µA; it is not the bias of the 13 mA operating point. Curves show plate current, transconductance and amplification factor varying with grid and plate voltages.

For mixer service the same sheets give plate voltage 125 V, cathode resistor 270 Ω, plate current 7 mA and oscillator injection 1.4 V RMS. Stated conversion transconductance is 2.9 mA/V. This must not be confused with the amplifier point’s 10 mA/V: operation and conditions differ. Grid-to-plate capacitance is 1.7 pF; input and output capacitances depend on connection and external shielding. For grounded-grid operation Sylvania distinguishes shielded and unshielded values and specifies grounding conditions in its notes.

Design-center limits include plate voltage 300 V, plate dissipation 4 W and cathode current 30 mA. Maximum grid-circuit resistance is 0.1 MΩ fixed bias, 0.5 MΩ cathode bias. Heater-cathode ratings distinguish total DC and peak 200 V, with an additional 100 V limit on the DC component when the heater is positive relative to the cathode. RCA’s two June 1957 sheets are marked tentative: they confirm these limits and principal characteristics without establishing an introduction or manufacture date for every specimen.

Bottom-view basing 7DK notably duplicates the plate and grid terminals: plate pins 1 and 7, grid 2 and 6, heater 3 and 4, cathode 5. It remains one triode, not two independent sections. Tung-Sol and RCA give maximum diameter 3/4 inch, overall length 1 3/4 inches and seated length 1 1/2 inches: converted values 19.05, 44.45 and 38.10 mm. Any mounting position is permitted. Documentation: Sylvania, Type 6AN4 UHF Triode, three pages; Tung-Sol, 6AN4, August and September 1953 sheets, three pages; RCA, 6AN4 High-Mu Triode, June 1957, two tentative pages preserved in two copies.