How do I measure output impedance? Reply #25 – 2015-07-08 14:28:16 Quote from: pdq on 2015-07-08 14:11:32Quote from: Arnold B. Krueger on 2015-07-08 13:24:07Transformers require careful engineering to avoid adding audible nonlinear distortion (particularly at low frequencies) and frequency response aberrations.Which is why it is so difficult to design a tube amplifier with very low distortion and flat response.Precisely. To that end any number of transformerless tubed power amps have been developed. Some of them are pretty good. They typically run into severe economic and reliability problems because of the vast number of tubes required to deliver large amounts of power into low impedance loads.