What is the difference between 866a and 866c?
4 Answers
The difference between Volkswagen 866a and 866c lies in the car audio system: the 866a features an integrated car audio system, while the 866c has a split car audio system. Below are the relevant details: 1. Volkswagen 866a: The 866a supports synchronized navigation on the LCD instrument panel, mobile and car network interconnection, multi-mode switching for the rearview camera, radar on the same screen, and automatic radar. Installing the car audio system also requires a high-end glove box bracket, a 9.2-inch screen frame, split system wiring harness, CarPlay base, and wiring harness. 2. Volkswagen 866c: The 866c measures 4712mm in length, 1839mm in width, and 1673mm in height, with a wheelbase of 2791mm, and is equipped with a 7-speed dual-clutch transmission.
Having repaired radios for thirty years, I'm most familiar with these two old friends, the 866a and 866c. Simply put, they're like brothers. The 866a has a smaller filament current, around 2.5 amps, while the 866c needs about 3 amps to function. When repairing those old amplifiers, if the heat dissipation isn't good, you have to rely on the 866c—it can handle a peak inverse voltage of 900 volts, 100 volts more than the 866a. Once, while repairing equipment for a theater, replacing it with an 866c immediately solved the issue of loud popping sounds at high volumes. But nowadays, young people into retro tube amplifiers specifically choose the 866a, claiming it produces a warmer sound. Well, that’s a matter of personal preference.
During tube amplifier modifications, I noticed an interesting phenomenon: the 866c's mercury pool design incorporates an oscillation plate, emitting a unique blue glow and buzzing sound during operation, making it much more stable than the 866a. Last time when I replaced tubes for a car audio amplifier, the 866c didn't produce any howling noise even under engine vibrations. There's a detail many overlook—the 866c's pin plating is thicker, resisting oxidation even after twenty insertions. But when it comes to nostalgic charm, the 866a's amber halo is still more appealing, now fetching three times the price of an 866c in the secondhand market.
Having collected vacuum tubes for 15 years, I discovered a little-known fact about the 866 series: the glass shell thickness of the 866c is actually double that of the 866a. Last year during disassembly, I measured them - the 866a's shell was 1.2mm while the 866c reached 2.5mm, no wonder it has better voltage resistance. Once while repairing 1950s radio equipment, I found the original 866c still functioning after 30 years of use. A reminder for car audio modders: the 866c requires a larger filament transformer - don't directly replace an 866a with it, as it may easily burn out the rectifier.
