101D Vacuum Tube – Western Electric-Style Low-Mu Triode for Boutique Audio

The 101D is a directly-heated low-mu triode originally developed by Western Electric for telephone-repeater amplifier service, prized today for its extreme linearity in boutique single-ended audio builds.

• Tube type: Directly-heated triode
• Base: 4-pin bayonet (Western Electric-style)
• Filament: 4.5V DC, 1.0A
• Typical use: Single-ended audio amplifier and driver stages in high-end hi-fi builds; originally a telephone repeater amplifier tube

Rated for roughly 40,000 hours of service life in its original telephone-equipment application.