How Does Diode String Affect IF AGC Amplifier Performance and JFET Class Operation?

Hello! Hope i find you all healthy!      First of all can somebody help me figuring out , with precise explanation and technical aproach about how does that diode string influence my AGC capabilities of the amplifier circuit ?  I mean i know that changing the VAGC voltage from the DR  input the Q point of the transistor changes and so does the amplification. But what is the matter with the diode string?   Secondly, a general question. Does the JFET transistor functional class ( A,AB,B,C..) varies in the same way as for the bipolar transistor ? I mean Vgs=Vp means class B and so on?   

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The six-diode string forces the source of JFET J2A2 to always be six diode drops 6*0.7volts=4.2volts positive with respect to ground. This makes the minimum gain (when AGC input DR=0volts) lower, increasing the AGC dynamic range.JFET functional class does vary similarly to bipolar-transistor functional class. However, the more gradual cutoff in JFETs will affect the details. Class C can be considered a primitive switching-mode amplifier where the switching clock is itself the signal.