
A 1956 Valve Amplifier That Sags Under You
A 1956 valve line amplifier with a power supply that can't keep up. Hit it hard and the rail sags, the valve's bias moves down with it, and the distortion changes character rather than just getting louder. The supply recovers slower than it fell, so a loud bar leans into the one after it.
It's happiest on drums, where that recovery between hits is most of the effect. On a mix bus it does the same thing to everything at once, more gently. Two controls do most of the work — SAG for how far the supply gives way, IRON for how hard the transformer is pushed.
How far the supply gives way. Turn it up and the distortion changes character rather than just amount, and every hit takes longer to recover than it took to fall.
IRON pushes the output transformer, adding low-end bloom and top-end resonance together. FLUX picks where the bloom sits: 25 to 250 Hz over six switched positions.
What seventy years did to this chassis: top-end loss, drifting bias and output level, mains hum, valve hiss. Nothing drifts in step, so it wanders rather than pulses.
The needle reads how far the supply fell during the last block, not gain reduction. It dips on the downbeat and comes back between phrases.