Transmitting Triode, air cooled ~ VHF
The VT67 Vacuum tube is a transmiting tube for
portable eqiuipment. It has a ceramic UX base.
It was used since 1934 in BC-222/223
'walkie-talkie'. It os derived from type 30.
The 30 was intended as detector or amplifier tube in portable radio receivers. It is a battery tube
like the 31 which was the tube of the month in January.
It has the same UX4 base and pinout as the 31 and also the same size bottle, ST-12.
Being intended for battery powered equipment it's oxide coated filament was designed to
operate at as little power as possible. The filament voltage is only 2V and needs a
measly 60mA to operate! That's only 120 milliwatts of filament power. The 30 is typically operated at
135V plate voltage (180V max) and at around 3mA bias current. It has a plate resistance of 10k Ohms
which makes it still usable with an interstage or line out transformer if they have enough primary
inductance. It is more easily usable with LC or RC coupling. The amplification factor is 9.3. I never
used the 30 myself. It could be an ideal companion for the 31 in a nifty flea power SET amp to drive
ultra efficient speakers, or as tweeter amp in active set ups, or maybe a nice little all DHT
headphone amp. The plate curves show the typical excellent linearity of directly heated triodes:
Electrical Data:
Filament Voltage .......................... 2.0 DC V
Filament Current ............................ 0.12 A
Preferred Substitute ......................... VT27, VT67, 30 Special.