Indeed, the era of valves has long passed, but they persist in unexpected ways! Many vintage valve radios are still operational, and numerous valves lie dormant in ‘junk boxes,’ waiting to be rediscovered. If only we could eliminate the need for high voltages! Fortunately, there is a valve, the ECC86, that functions with a mere 6 V. In the early 1960s, the electronics industry faced a dilemma. With the advent of transistors, it became feasible to create car radios without vibrators and bulky transformers. However, the transistor’s limited cut-off frequencies hindered the construction of viable VHF mixer stages. Consequently, valves were still necessary components in transistor circuits.
Low-Voltage Valve ECC86 for Car Receivers
The ECC86, a unique low-voltage valve, was specifically designed for shortwave input stages and self-oscillating mixer stages in car receivers directly powered by the car battery. Its datasheet indicated compatibility with either 6.3 V or 12 V anode voltage while maintaining a constant 6.3 V heater voltage. This valve’s existence can be attributed to a distinct bottleneck in electronics technology history, shaping its purpose and applications.
Circuit Design and Signal Amplification
The circuit utilizing the ECC86 resembles a classical valve audion tailored for the medium-wave range. A 6-V lead-acid gel battery supplies power, forming a configuration akin to a two-stage amplifier. The initial stage handles demodulation and preamplification, while the subsequent stage acts as the audio output amplifier, directly powering a 2 kΩ impedance headphone. A crucial element, a 500-pF capacitor, strategically placed between the stages, prevents further amplification of RF signals. Without this component, the valve might revert to its original purpose and oscillate within the short-wave spectrum.
Aerial Setup and Reception Quality
To enhance reception, a ferrite rod measuring 10 mm in diameter and 100 mm in length, wound with 50 turns of enameled copper wire, serves as the aerial. This setup enables the radio to deliver excellent sound quality while receiving local signals. In the evening, connecting a sufficiently long external aerial allows the radio to capture numerous medium-wave stations effectively, evoking a sense of nostalgia reminiscent of the past era of radio technology.