Ampera
421A
Dual Triode · IHT · Octal · 1953
“WE-branded 5998. Audiophile grail OTL tube.”
Power triode delivering 13W for push-pull and SET designs
GAIN FACTOR0
PLATE IMPEDANCE0Ω
TRANSCONDUCTANCE0mA/V
GAIN5%
POWER33%
DRIVE100%
LINEARITY95%
EXECUTIVE SUMMARY
The 421A is a dual indirectly-heated triode from Western Electric, introduced around 1953. It provides a gain factor (μ) of 5.4 with 350Ω plate resistance. Commonly used in power/output applications. WE-branded 5998. Audiophile grail OTL tube.
APPLICATIONS
SET outputPush-pull outputHeadphone outputPhase splitter
Generic triode power/output stage
• Hi-Fi stereo• Headphone amp
VS 5998
HISTORY
Introduced1953ManufacturerWestern ElectricEquivalents5998, 7236
Golden AgeSPECIFICATIONS
Heater Voltage6.3V
Heater Current2.5A
Max Plate Voltage250V
Max Power13W
Sensitivity15.5 mA/V
Gain Factor5.4
Internal Impedance350Ω
PinoutOctal
Era1953
RarityLegendary
SPICE model not yet available. Loadline calculator requires calibrated Koren parameters.