307A National Union VT-225

307A (VT-225) is Moderate-power, filamentary
suppressor-grid pentode for audio-frequency amplifier or modulator

Class A audio amplifier characteristics

Plate Voltage Screen Voltage Suppressor Voltage Control Bias Plate Current Screen Current Load Resistance Input Voltage Power Output Second Harmonic Third Harmonic
Volts Volts Volts Volts mA mA Ohms Peak Volts Watts db db
200 200 0 -15 36.5 3.4 4000 0-15 2.9 23.5 24
250 250 0 -20 50 4.0 4000 0-20 5.7 24 23.5
300 300 0 -30 43 2.6 4500 0-30 9.1 21 17.5

  Limiting Conditions for safe use:  Maximum
plate dissipation is 15 watts, screen-grid dissipation is 6 watts,

500 300     60 25          

Filament voltage 5.5 volts, A.C. or D.C.    
Nominal filament current 1.0 ampere

 

This tube works really nice in SE or PP

One of my favorite audio tubes VT225 / 307A
/ 306A, specially
triode strapped and a bit overrated. The National Union version is exact Western
Electric equivalent, with four holes at both ends of plate.


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