Based on the Orange® OR80
No Master, HF drive=Presence
Controls: FAC(mid range tone control by 6 pos switch) – Bass – Treble – H.F Drive(presence) – Gain
Output: 80 Watts
Preamp tubes: 12AX7
Bias: Fixed bias
Rectifier: solid state
Phase Inverter: Cathodyne type: 1/2 x 12ax7
The F.A.C. control stands for Frequency Analysing Control. It is a mid-range sweep that offers many variations on the Orange sound. Experiment with different settings for a variety of sounds. It is basically EQ settings from bassy all the way to the left and getting progressively thinner as you go to the right. Most people, set it all the way to the left or one click to the right from that.The FAC control switches between different interstage coupling capacitors which will change the low frequency cutoff/rolloff point of the preamp. In other words, it cuts bass increasingly with each click clockwise.
The HF drive is a presence control, that boost/attenuate very high frequencies, comparing to other amplifiers. It’s in between gain stages (2 to 3), so it does effect drive. You can call it a drive control, like the Eq, that is between stage 1 and 2.