7247

7247 has no equivalent designation confirmed by the archive. Completed sales put the typical price at $28.53 per tube.

The 7247 is a dissimilar double-triode designed for use in high-fidelity audio amplifiers. It has a coated unipotential cathode and a T-6½ glass envelope with an E9-1 small button 9-pin base.

Construction

The 7247 contains two triode sections with different characteristics. Section 1 is similar to one section of a 7025 and is intended for low-level, high-gain stages where low hum and microphonism are desired. Section 2 is similar to one section of a 12AU7 and is intended for cathode follower or phase-inverter service. Section 1 connects to pins 6, 7, and 8; Section 2 connects to pins 1, 2, and 3. Pin 1 is the plate of Section 2, pin 2 is the grid of Section 2, pin 3 is the cathode of Section 2, pin 6 is the plate of Section 1, pin 7 is the grid of Section 1, and pin 8 is the cathode of Section 1. Pins 4 and 5 are heater connections, and pin 9 is the heater center-tap. The EIA base diagram for the 7247 is 9A.

Ratings

The heater can be operated in series at 12.6 ± 1.3 volts with 0.15 amperes current, or in parallel at 6.3 ± 0.6 volts with 0.3 amperes current. The maximum plate voltage is 330 volts for both sections. The maximum positive DC grid voltage is 0 volts for both sections, and the maximum negative DC grid voltage is -55 volts for both sections. Maximum plate dissipation is 1.2 watts for Section 1 and 3.0 watts for Section 2. Maximum DC cathode current for Section 2 is 22 milliamperes. The maximum DC component of heater-cathode voltage with heater positive with respect to cathode is 100 volts for both sections; the maximum total DC and peak heater-cathode voltage is 200 volts for both sections, with heater either positive or negative with respect to cathode. Maximum grid-circuit resistance with fixed bias is 15 megohms for Section 1 and 0.5 megohms for Section 2; with cathode bias it is 1.0 megohm for Section 2.

Characteristics

For Section 1, representative operating points include a plate voltage of 100 volts with a grid voltage of -1.0 volts, and a plate voltage of 250 volts with a grid voltage of -2.0 volts; at both points the amplification factor is 100. Approximate plate resistance is 80,000 ohms at 100 volts and 62,500 ohms at 250 volts. Transconductance is 1250 micromhos at 100 volts and 1600 micromhos at 250 volts. Plate current is 0.5 milliamperes at 100 volts and 1.2 milliamperes at 250 volts. For Section 2, representative operating points include a plate voltage of 100 volts with a grid voltage of 0 volts, where the amplification factor is 20, and a plate voltage of 250 volts with a grid voltage of -8.5 volts, where the amplification factor is 17. Approximate plate resistance is 6,500 ohms at 100 volts. Transconductance is 3100 micromhos at 100 volts and 2200 micromhos at 250 volts. Plate current is 11.8 milliamperes at 100 volts and 10.5 milliamperes at 250 volts.

Capacitance and Noise

Direct interelectrode capacitance from grid to plate is 1.7 picofarads for Section 1 and 1.4 picofarads for Section 2. The average equivalent noise and hum voltage for Section 1, referred to the grid, measured under specified conditions, is 1.8 microvolts true RMS, with a maximum of 7.0 microvolts true RMS.

Mounting

The 7247 can be mounted in any position.

Base B9A, viewed from below (the wiring side), pins numbered clockwise from the key. Read from the datasheet's basing table and checked against it automatically — confirm against the original datasheet before wiring.

Per-tube prices from completed sales, 2026-07-22 to 2026-09-28. Matched pairs and quads are divided out. See the price index for how these move over time.

Original manufacturer datasheets for 7247, hosted by Frank Philipse's Electron Tube Data sheets.

Documents held here and used to write this page.

• 7247