6C4

6C4 is also designated EC90. Completed sales put the typical price at $9.21 per tube.

The 6C4 is a miniature, medium-mu triode suitable for use in a wide variety of general-purpose applications. It has a T-5½ glass envelope and an E7-1 miniature button 7-pin base, and may be mounted in any position. The heater is rated at 6.3 volts and 150 milliamperes.

Construction

The tube is an indirectly heated triode. Pin 1 and pin 5 are the plate, pin 6 is the grid, and pin 7 is the cathode. Pins 3 and 4 are the heater connections. Pin 2 is an internal connection.

Ratings

For Class A1 amplifier service, the design-center plate voltage rating is 300 volts. For Class C telegraphy service, the design-center ratings are 300 volts plate voltage, 5.0 watts plate dissipation, 25 milliamperes DC plate current, and 8.0 milliamperes DC grid current. The maximum grid-circuit resistance is 0.25 megohm with fixed bias and 1.0 megohm with cathode bias. Maximum heater-cathode voltage is 100 volts DC component with the heater positive with respect to the cathode, and 200 volts total DC and peak with the heater either positive or negative with respect to the cathode.

When used as an R.F. power amplifier or oscillator for frequencies up to 150 MHz, the maximum anode voltage is 550 volts (or 300 volts per another rating), the maximum anode dissipation is 3.5 watts, and the maximum cathode current is 30 milliamperes for oscillator or amplifier service, or 20 milliamperes for doubler or trebler service. The maximum grid voltage is 100 volts, the maximum grid current is 5.0 milliamperes, and the maximum grid resistor is 250 kilohms. The maximum voltage between cathode and heater is 150 volts, and the maximum bulb temperature is 180 degrees Celsius.

Characteristics

At a plate voltage of 250 volts and a grid voltage of -8.5 volts, the amplification factor is 17, the plate resistance is approximately 7700 ohms, the transconductance is 2200 micromhos, and the plate current is 10.5 milliamperes. The grid voltage is approximately -25 volts at a plate current of 10 microamperes. The direct interelectrode capacitance from grid to plate is 1.4 micromicrofarads with a shield and 1.6 micromicrofarads without a shield; the input capacitance from grid to heater plus cathode is 1.8 micromicrofarads with or without a shield.

Applications

The 6C4 is especially useful as a local oscillator in high-frequency and very-high-frequency receiver circuits. When used as an oscillator at 150 megacycles with a grid resistor of 10,000 ohms and maximum rated input, it can produce a power output of 2.5 watts. The tube is also designed for use as an R.F. power amplifier or oscillator for frequencies up to 150 MHz.

Equivalence is asserted only where the archive's own literature states it directly, in at least 40 separate documents. Tubes that merely substitute in some circuits are not listed here.

Per-tube prices from completed sales, 2026-08-12 to 2026-09-22. Matched pairs and quads are divided out. See the price index for how these move over time.

Original manufacturer datasheets for 6C4, hosted by Frank Philipse's Electron Tube Data sheets.

Documents held here and used to write this page.

• DESCRIPTION AND RATING=
• EC90 (filed under EC90)

2 further designations appear alongside 6C4 in the literature but below the evidence threshold used here, so they are not listed as equivalent.