This is an interesting triode for several reasons,

• It has one anode and one cathode but effectively two heaters, so you can operate it in two different modes,

  • One heater on, either the left or the right, and this referred to as single cathode operation and has more limited anode current and power, 350mA and 45W respectively.

  • Dual heater operation, either in series or parallel, gives twin cathode operation, with increased maximum anode current and power, 600mA and 60W respectively.

• The heaters are quite powerful, and in parallel connection (6.3V) require up to 7.2A, and in series connection (12.6V) they require up to 3.6A.

• This triode has very low anode resistance, less than 130 Ohms according to the datasheet, but this will of course depend on the operating point.

• The warm up time for the cathode is quite slow, with the datasheet quoting a maximum of 120 seconds.

• The gain of the triode is low, between 1.5 and 3.0, depending on operating point.

Three sets of curves and models are produced for this valve due to its different operating modes,

• 6c33c_1: This is with the left heater on only (pins 1&2), single cathode mode.

• 6c33c_2: This is with the right heater on only (pins 6&7), single cathode mode.

• 6c33c_3: This is with both heaters on, dual cathode mode.