12GT5A — Beam Power Pentode
The 12GT5A is a Novar-type beam power pentode designed primarily for horizontal deflection amplifier service in television receivers. It features a 12.6-volt heater with controlled warm-up time and is characterized by its compact Novar T-12 envelope construction.
Physical Construction and Dimensions
The 12GT5A is constructed using the Novar T-12 glass envelope configuration. It utilizes a Novar Button 9-pin base, designated as the E9-88 base type, which features an exhaust tip located at the bottom of the base. The physical outline of the tube is designated as 12-95.
The physical dimensions of the 12GT5A are specified as follows:
- Maximum Diameter: 1.562 inches
- Maximum Seated Height: 2.500 inches
- Maximum Overall Height: 2.880 inches
The "A" revision of this tube series (which includes the 12GT5A, 6GT5A, and 17GT5A) represents a physical redesign compared to the original non-A versions (12GT5, 6GT5, and 17GT5). The 12GT5A is identical to the older 12GT5 except for this physical construction, which incorporates a shorter glass bulb and a base design with the exhaust tip located at the bottom.
Heater Specifications and Pinout Configuration
The 12GT5A is designed for series or parallel heater circuits, featuring a controlled warm-up time. The heater characteristics and ratings are:
The tube uses the 9NZ basing arrangement, which provides the following pin connections when viewed from the underside of the base:
The duplicate connections for Grid No. 1 (Pins 2 and 6) and Grid No. 2 (Pins 3 and 7) are typical of high-performance beam power tubes, allowing for flexible circuit layout and improved heat dissipation or reduced lead inductance. Pin 8 is designated as an internal connection and should not be used for external circuit tie points.
Related Designations and Family Variations
The 12GT5A belongs to a closely related family of beam power tubes designed for horizontal deflection amplifier service. These tubes share identical internal structures and electrical characteristics, differing primarily in their heater configurations or physical envelope designs:
- 6GT5A: The 12GT5A is electrically and physically identical to the 6GT5A, with the sole exception of the heater ratings. The 6GT5A is designed for a different heater supply voltage and current.
- 17GT5A: This is another family member sharing the same construction and characteristics, differing only in its heater requirements.
- 12GT5: The 12GT5 is the predecessor to the 12GT5A. The 12GT5A is identical to the 12GT5 except for the base construction (which features the bottom exhaust tip) and the shorter bulb height of the "A" version.
- 6GT5 and 17GT5: These represent the non-A versions of the corresponding 6-volt and 17-volt family members, which also feature the taller bulb and lack the bottom exhaust tip design of the "A" suffix variants.
Technical Summary
The 12GT5A is a Novar-type beam power pentode housed in a compact T-12 glass envelope with a 9-pin E9-88 button base. Specifically engineered for horizontal deflection amplifier service, the tube features a 12.6 V, 0.600 A heater with an average 11-second warm-up time. It utilizes the 9NZ basing diagram, providing dual connections for both the control grid (Grid No. 1) and screen grid (Grid No. 2) to facilitate circuit layout. As an "A" suffix variant, it is distinguished from the original 12GT5 by its shorter bulb and bottom-positioned exhaust tip, while remaining electrically identical to the 6GT5A except for its heater ratings.
