The McIntosh MC3500 MKII is a 350-watt power amplifier with eight EL509S high-power output vacuum tubes. It’s a single-channel amplifier that costs $15,000, meaning you’ll have to drop $30,000 ...

The United States also adopted this late after the end of World War II, and in the 1950s, the adoption of magnetic amplifiers in weapons such as automatic control devices, fire control systems ...

The K2-W vacuum-tube op amp has an LTspice-simulated open loop gain of 27,000. The modeled K2-W input impedance is >100 MΩ. The LTspice modeled result shows 1.00 nA of input current.