ECC83S

The JJ Electronic ECC83S is a modern implementation of the high-amplification-factor twin triode in the ECC83 family. The manufacturer sheet also lists 12AX7 and 7025 and describes it as an audio-frequency twin triode. The documentation includes plate curves, transfer characteristics and examples of resistance-coupled amplifiers with cathode bias, defining its use in voltage-amplification stages. Photographs show shaped anodes, internal shields and mica supports; these construction features alone do not measure the microphonics of each specimen.

The typical operating point is 250 V plate voltage and −2 V grid voltage, with 1.2 mA plate current per system. Transconductance is 1.6 mA/V, internal resistance 62.5 kΩ and amplification factor μ is 100. This last figure characterizes the triode and does not automatically equal the gain of a practical stage. Capacitances are identical for both sections: 1.6 pF grid-to-cathode, 1.7 pF grid-to-plate and 0.33 pF plate capacitance. The graphs allow other operating points to be compared while keeping typical values separate from limits.

The centre-tapped heater requires 6.3 V and 300 mA with the two halves in parallel, or 12.6 V and 150 mA in series. The base is noval: groups 1–2–3 and 6–7–8 correspond respectively to plate, grid and cathode of the two triodes; pins 4 and 5 are the heater ends and 9 the centre tap. The JJ drawing gives a maximum diameter of 22 mm, an envelope height of 49.2 mm and overall height of 56.3 mm. Listed limits include 300 V plate voltage, 1 W plate dissipation, 8 mA cathode current, 180 V between cathode and heater and 2.2 MΩ grid resistance.

The circuit examples show why supply voltage must not be confused with actual plate voltage. With a 250 V supply, 100 kΩ plate resistor, specified 330 kΩ grid resistor and 1.5 kΩ cathode resistor, JJ gives 0.86 mA plate current. The same table includes a 400 V supply with 100 kΩ plate resistance, 330 kΩ grid resistance and 820 Ω cathode resistance, yielding 1.72 mA. The 400 V is the supply voltage before the plate resistor and does not change the 300 V plate limit. These examples illustrate the relationship between supply, load and bias; they are not a universal specification for every preamplifier.