6JC8

The 6JC8 combines a medium-mu triode and a sharp-cutoff pentode. General Electric primarily intends it as a triode oscillator combined with pentode mixer in VHF applications; RCA’s manual specifies television oscillator-mixer service. The sections perform different functions in one envelope: having a triode does not make it a generic twin audio amplifier.

The heater is nominally 6.3 V, 0.45 A, AC or DC, with controlled average warm-up time 11 seconds. The sheets distinguish series operation at 0.45 ± 0.03 A from parallel at 6.3 ± 0.6 V. General Electric defines warm-up as reaching 80% of rated voltage in its specified test circuit, not a guarantee that every appliance becomes fully operational after 11 seconds.

At plate 125 V and grid −1 V the typical triode point gives 12 mA, transconductance 6.5 mA/V, amplification factor 40, plate resistance approximately 6 kΩ. The pentode at plate and screen 125 V, control −1 V gives plate current 9 mA, screen current 2.2 mA, transconductance 5.5 mA/V, plate resistance approximately 300 kΩ. These are individual-section characteristics at those conditions, not automatically mixer conversion-gain specifications.

Design maxima: plate voltage 275 V for either section, plate dissipation 1.7 W triode and 2.3 W pentode. RCA specifies pentode screen dissipation 0.45 W up to 137.5 V, with voltage-dependent limit above that point referring to a chart also included by General Electric. Maximum pentode control-grid resistance: fixed bias 0.1 MΩ, cathode bias 0.5 MΩ. Capacitances depend on shielding: pentode control grid to plate maximum 0.038 pF unshielded versus 0.018 pF shielded; RCA specifies external JEDEC 315 shield connected to pin 3 for these data.

The Noval B9A E9-1 base uses arrangement 9PA. Bottom view: 1 and 7 cathode, pentode suppressor and internal shield; 2 pentode control grid, 3 pentode screen, 4 and 5 heater, 6 pentode plate, 8 triode grid, 9 triode plate. Plates and control grids remain separate, while cathode and shield connections must follow the stated arrangement.

RCA and General Electric give maximum overall length 2 3/16 inches = 55.5625 mm, maximum seated height 1 15/16 inches = 49.2125 mm, maximum diameter 22.225 mm. RCA also gives minimum diameter 19.05 mm. Body excluding tip 1 9/16 ± 3/32 inches = 39.6875 ± 2.38125 mm; bulb T-6½, any mounting position. Documentation: General Electric, 6JC8 Triode-Pentode, ET-T3028, December 1961, curves dated 25 September 1961; RCA Electron Tube Division, 6JC8 Medium-Mu Triode—Sharp-Cutoff Pentode, May 1962; RCA Receiving Tube Manual RC-30, 6JC8 entry, pages 317–318.