6DC6

The 6DC6 is a miniature variable-mu pentode described by RCA, Sylvania and Tung-Sol as semi-remote-cutoff. It is intended chiefly for gain-controlled picture IF stages in colour and monochrome television receivers and for RF amplification in their tuners. Changing control-grid bias changes transconductance and thus permits gain control. It is a signal amplifier, not a power-output tube.

Indirect heating requires 6.3 V at 0.3 A, AC or DC; any mounting position is allowed. The seven-contact miniature B7G base uses diagram 7CM: 1 control grid, 2 cathode, 3 and 4 heater, 5 plate, 6 screen grid, 7 suppressor and internal shield. Typical data require the suppressor to be connected to the cathode at the socket. This external connection is part of the specified conditions, not an internal connection to be assumed.

The typical class-A1 point specifies a 200 V plate supply, 150 V screen voltage and 180 Ω cathode resistor. Plate current is 9 mA, screen current 3 mA, approximate plate resistance 0.5 MΩ and transconductance 5.5 mA/V. Approximately −12.5 V grid voltage instead refers to transconductance reduced to 50 µA/V, not bias at the 9 mA operating point. Transfer curves show how currents and transconductance change with grid control and screen voltage.

Design-center limits include 300 V plate voltage and 2 W plate dissipation. Screen supply may reach 300 V, but that does not freely permit 300 V directly on the screen: allowable screen voltage and dissipation follow the derating curve. RCA RC-30 specifies 0.5 W through 150 V screen voltage and refers to the curve above that value. Control and suppressor grids must not have positive bias. Maximum control-grid circuit resistance is 0.25 MΩ with fixed bias and 1 MΩ with cathode bias. With the heater positive relative to the cathode, RCA and Sylvania distinguish 200 V total peak and 100 V DC component; with the heater negative they specify 200 V.

Without an external shield, grid-to-plate capacitance is at most 0.02 pF, input capacitance 6.5 pF and output capacitance 2 pF. Construction uses a T-5½ bulb and JEDEC E7-1 button base. RCA and Tung-Sol give maximum diameter 3/4 inch, overall height 2⅛ inches and seated height 1⅞ inches: 19.05, 53.975 and 47.625 mm. RCA gives base seat to bulb top excluding the tip as 1½ ±3/32 inches, or 38.1 ±2.38125 mm. Dimensions with and without the tip, and those including pins, remain distinct.

A documentary peculiarity is the sharp-cutoff heading in RCA RC-30, whereas the dedicated sheets from all three manufacturers agree on semi-remote-cutoff. This discrepancy must not be turned into an undocumented second version. Documentation: RCA 6DC6, tentative data dated June 14, 1954 and curves; Tung-Sol 6DC6, July 1, 1954, plates 3843–3844; Sylvania Type 6DC6, two pages; Sylvania Engineering Data Service 6DC6, July 1956, six pages; RCA Receiving Tube Manual RC-30, page 241.