Dome-type or Aubergine-type bulb of glass, a white ceramic base with four-prong bayonet golden pins, oxide coated filamentary, solid plate or mesh or carbon plate triode. 


Audio frequency amplifier where power outputs of approximately 8.5watts or less is required at relatively low plate voltages.


Dimensions, outline diagrams of the tube and bases, and the arrangement of electrode connections to the base terminals are shown in Figures 1, 2 and 3.

TJ Fullmusic 300B DIY Hifi Supply


   Nominal operating conditions and parameters 

Filament voltage* : 5V or 2.5V

Nominal filament current : 1.2A or 2.4A

Plate voltage : 300V

Grid voltage** : -58V

Plate current : 60mA

Amplification factor : 3.85

Grid to plate transconductance : 5.7mA / V 

Grid current : 0.05 μ A

Plate resistance: 700 ohms

*Alternating-current filament supply or Direct-current filament supply.

**Alternating-current filament supply is used. The grid and plate returns should be connected to a center tap on the secondary of the filament transformer. Direct-current filament supply is used. The grid and platter returns are connected to the negative end of the filament.

Characteristics-Average characteristics 

Figure 4. shown typical curves of plate currents of grid voltage for several values of plate voltages. It is alternating-current filament supply.


TJ Fullmusic 300B DIY Hifi Supply  Fig. 4

Limiting Operation Conditions for Safe Nor simultaneous ratings 

Maximum plate voltage : 450 volts

Maximum plate dissipation : 40 watts

Maximum plate current of average tube for fixed gird bias  : 70mA

Maximum plate current of manually adjusted gird or self-biasing circuit : 100mA