NOS RCA 5U4GB T1 Fat Base Black Plate Dual-D Getter Rectifier Tested 2300/2300

NOS RCA Radiotron 5U4GB T1 Fat-Base Black-Plate Rectifier Tube - Made in USA

This is an early-production RCA 5U4GB full-wave rectifier dating to approximately 1954–1955, based on its distinctive internal and base construction. It is NOS unused old stock and has been energized only for testing.

CONSTRUCTION

This is the collector-designated RCA “T1” version featuring:

• Wide flanged/fat barrier base
• Smooth matte-black plates
• Vertical plate ridges with five crimps per side
• Seven-point mica support
• Two hanging rectangular/D getters
• Silver RCA Radiotron Electron Tube printing
• Standard keyed octal connection
• Intact guide key and straight pins

“T1” is collector terminology used to distinguish this earliest RCA 5U4GB construction; it was not an official RCA model suffix. The “7AC” marking visible on the tube is RCA’s basing designation.

TEST RESULTS

Tested on a laboratory-grade tube tester:

• Section 1: 2300 on the tester’s Gm/conductance scale
• Section 2: 2300
• Current: 36.4 / 36.4 mA
• No shorts detected

The provided tester reference is 1800 minimum-good and approximately 2200 expected-new. Both sections exceed that reference and produced equal readings within the tester’s displayed resolution.

Because the 5U4GB is a rectifier rather than an amplifying tube, the 2300 readings are reported exactly as displayed on the tester’s conductance/Gm scale.

CONDITION

NOS with clean glass, unusually strong original printing, a tight base, straight pins and an intact guide key. The getter deposits remain metallic gray, with no visible indication of lost vacuum.

Reverb condition is listed as Excellent because this is a privately sold vintage item without its original packaging or manufacturer warranty. “NOS” describes its unused history; it does not mean the tube is being represented as a modern Brand New retail product.

Please examine the photographs, which show the exact tube being offered.

BOX

The pictured RCA box is included for storage and protection but is not original to this tube. The tube is therefore described as NOS, not NIB.

COMPATIBILITY AND PHYSICAL FIT

The 5U4GB is a directly heated full-wave rectifier requiring a 5-volt, 3-amp filament supply and a compatible keyed octal socket. It should be used only in equipment designed for a 5U4GB or expressly approved for one.

Equipment known to specify a 5U4GB includes the Magnavox 185AA, Dynaco/Dynakit Mark II and EICO HF-20. The McIntosh MC60 specifies two 5U4GB rectifiers, so this single tube would serve as one replacement or spare.

This early T1 construction has a wider base flange than later RCA 5U4GB versions. The lower keyed portion fits a standard octal socket, but buyers should verify clearance around recessed sockets, spring or bear-trap retainers, tube cages, transformers and neighboring tubes.

Do not assume interchangeability with equipment specified only for a 5AR4/GZ34, 5V4, 5Y3, 5R4 or 274B. Electrical requirements and operating characteristics differ.

INCLUDED

• One NOS RCA Radiotron 5U4GB T1 rectifier tube
• Pictured non-original RCA storage box

The tube will be carefully cushioned and securely packed for shipment.

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