This exhibit is a modern production ECC82 from China. The ECC82 was designed as an audio and general purpose double triode. The 6C4 RF triode has almost the same rating as half of an ECC82.
An amplification factor of 17 is quoted, which is much lower than that for the pin compatible ECC83 at 100.
Modern valve production is for the audio market and this exhibit came as part of a valve headphone amplifier operating at 24 Volts from a switch mode brick. The valve is used as a voltage amplifier driving a MOSFET output stage, one per channel.
The production is in keeping with earlier versions.
The Bravo Audio headphone amplifier. The input is at line level through phono sockets or 3.5 mm jack. The output is to a standard stereo jack with 3.5 mm adaptor. The heatsinks at the back are for the power MOSFETs. The heatsinks run very hot with a 24 V supply but using a 15 V supply the heatsinks are hot but do not burn. Also the audio performance with a 15 V HT is very good. At 13.8 V the circuit does not function correctly.
Specifications: Power: DC 24 V, Input Sensitivity: 100 mV, Input Impedance: 100 kΩ Out-Put Impedance: 20~600 Ω, Gain: 30 dB, Frequency response: 10Hz-60KHz ± 0.25 dB, Signal/Noise Ratio: gt 90 dB, Dynamic range: 84.6 dBA(300 Ω) 89.8 dBA(33 Ω); THD: 0.016%(300 Ω) 0.45%(33 Ω), IMD + Noise: 0.045(300 Ω) 0.42(33 Ω), Dimension:79 mm (D) X 79 mm (W) X 44 mm (H)not including the valve, Shipping Weight: 600 g.
A MOSFET headphone amplifier design by Greg J Szekeres can be seen by following the link. The image above is a variation by Tomohiko Ishigami.
Face-on it is an elegant device. An LED in the centre of the base lights-up in use.
Side view. The large capacitor at the left is across the supply input.
The rear view. The smaller un-painted heatsinks are used for the regulators that supply both heater voltage and current for the MOSFETs.
The thin glass tube envelope is 22 mm in diameter and the length excluding the B9A base pins, is 48 mm.
References: Data-sheet & 1040. Type ECC82 was first introduced in 1951.