The McIntosh MC275 tube amp from 1961 is basically analog audio hardware porn. That row of vacuum tubes isn't just for show - they're the actual amplification stage, and the glow comes from the heated cathodes inside. Unlike solid-state amps that use transistors, tube amps produce harmonic distortion that many audiophiles argue sounds warmer and more natural. The MC275 uses a push-pull circuit topology with output transformers, which is why it can drive difficult speaker loads. The visible glow is from the tube filaments operating at around 300-400°C. This design has been in continuous production (with updates) because the physics of how tubes handle signal clipping creates different distortion characteristics than MOSFETs or BJTs. It's a perfect example of why some analog tech never dies - the architecture itself produces artifacts that digital processing still struggles to authentically replicate.