10EW7 — Dissimilar Double Triode

The 10EW7 is a miniature, dissimilar double triode vacuum tube designed primarily for use in television receivers as a combined vertical-deflection oscillator and vertical-deflection amplifier. It contains two highly distinct triode units within a single envelope: Unit No. 1 is a high-mu triode intended for oscillator service, while Unit No. 2 is a low-mu, high-current triode designed for power amplification in vertical deflection circuits.

The 10EW7 belongs to a family of identical tubes that includes the 6EW7, 15EW7, 19EW7, and 20EW7, which differ only in their heater voltage and current ratings.

Construction, Physical Dimensions, and Base

The 10EW7 features a 9T9 bulb design, which consists of a T-9 glass envelope with a 1-1/8 inch diameter based to fit standard 9-pin miniature sockets. The physical dimensions of the tube are:

• Maximum Diameter: 1.188 inches
• Maximum Seated Height: 2.620 inches
• Maximum Overall Height: 2.930 inches

The tube utilizes a coated unipotential cathode for each triode section. It can be mounted in any position.

Socket and Base Terminology

Different manufacturers use varying terminology to describe the physical construction and socket requirements of the 10EW7:

• Some documentation lists the construction as 9T9 with a Button 9-Pin (E9-68) base and a 9-70 outline.
• Other sources describe the tube as a Miniature type requiring a miniature 9-contact socket (with outline 6E) or as a Neonoval type requiring a neonoval 9-contact socket (with outline 10C).
• It is also described as utilizing a 9T9 bulb based to fit most standard 9-pin miniature sockets, with JEDEC outline 9-70 and base E9-68.

Pinout and Basing Diagram

The tube uses the 9HF basing arrangement, which provides the following pin connections (viewed from the bottom of the tube):

Unit No. 1 (the oscillator section) is connected to pins 6, 7, and 8. Unit No. 2 (the amplifier section) is connected to pins 1, 2, 3, and 9. The grid of Unit No. 2 is internally connected to both Pin 2 and Pin 3.

Heater Characteristics

The heater of the 10EW7 is designed for series-string or parallel operation. For series heater operation, equipment must be designed so that at normal supply voltage, bogey tubes will operate at the rated heater current.

The heater warm-up time is defined as the time required for the voltage across the heater to reach 80% of its rated voltage after applying four times the rated heater voltage to a circuit consisting of the tube heater in series with a resistance equal to three times the nominal heater operating resistance.

Heater-Cathode Voltage Ratings

The maximum ratings for the voltage between the heater and cathode are:

• Heater negative with respect to cathode: 200 V (Total DC and Peak)
• Heater positive with respect to cathode:
  • DC: 100 V
  • Total DC and Peak: 200 V

Electrical Characteristics and Class A1 Operation

The two triode sections of the 10EW7 have highly dissimilar electrical characteristics, optimized for their respective roles:

Additional Operating Points (Unit No. 2)

• Plate Current at $E_b = 60$ V, $E_c = 0$ V (Instantaneous): 95 mA
• Plate Current at $E_c = -25$ VDC: 8 mA

Cutoff Characteristics

• Grid Voltage (Approx.) for $I_b = 10$ $\mu$A (Unit No. 1): -20 V
• Grid Voltage (Approx.) for $I_b = 100$ $\mu$A (Unit No. 2): -40 V

Direct Interelectrode Capacitances

The direct interelectrode capacitances are measured without an external shield:

Vertical-Deflection Service Ratings

The 10EW7 is rated under the Design-Maximum Rating System for operation in a 525-line, 30-frame television system.

Pulse Duration and Duty Cycle Discrepancies

For the peak positive-pulse plate voltage rating of Unit No. 2 (1,500 V), the pulse duration must be strictly limited. However, different manufacturer manuals specify this limit differently:

• Some specifications state that the pulse duration must not exceed 15% of a vertical scanning cycle (which corresponds to 2.5 milliseconds).
• Other specifications state that the duty cycle of the voltage pulse must not exceed 15% of one horizontal scanning cycle.

Grid Leak Bias Protection

In stages operating with grid leak bias, an adequate bias resistor or other suitable means is required to protect the tube in the absence of excitation.

Average Plate Characteristics and Curves

The average plate characteristics of the 10EW7 are documented as follows:

• For Unit No. 1 (the oscillator section), the average plate characteristics are identical to those of Unit No. 1 of the 6DE7.
• For Unit No. 2 (the amplifier section), the average plate characteristics are shown in the published curves. The curves plot plate current (ranging from 0 to 140 mA) against plate voltage (ranging from 0 to 400 V) for grid voltages ($E_c$) from 0 V down to -65 V. These curves illustrate the high-current capability of Unit No. 2 at low plate voltages (e.g., 95 mA at 60 V and 0 V grid bias) and its low plate resistance, which is ideal for driving vertical deflection coils.

Related Designations and Heater Variations

The 10EW7 is part of a family of dissimilar double triodes sharing the same internal structure, pinout (9HF), and electrical characteristics, but utilizing different heater configurations:

These tubes are electrically identical in their triode characteristics and ratings, meaning that their operating points, capacitances, and maximum ratings are interchangeable, provided the appropriate heater supply is used.