Arkless Electronics
Trade: Amp design and repairs.
These measurements allow us to compare the response of the amplifier into both a flat and a simulated speaker load (black trace) with 10dB feedback or with no feedback
https://www.stereophile.com/content/cary-audio-cad-805rs-monoblock-power-amplifier-measurements
Fig.2 Cary CAD-805RS, 845 tube, 10dB feedback, frequency response from 4 ohm tap at 2.83V
into: simulated loudspeaker load (gray), 8 ohms (blue), 4 ohms (magenta), 2 ohms (red) (1dB/vertical div.).
Fig.3 Cary CAD-805RS, 845 tube, 0dB feedback, frequency response from 16 ohm tap at 2.83V
into: simulated loudspeaker load (gray), 8 ohms (blue), 4 ohms (magenta), 2 ohms (red) (1dB/vertical div.).
Really bad design there with the peaking at LF when NFB used!