15-11-2016, 07:14 PM
(15-11-2016, 03:02 PM)Refugee Wrote: It is biasing the IF amp transistor to get something like the effect of a variable MU pentode.
No, not at all!
By altering the bias and, therefore, the collector current, it is altering the voltage drop across R9 for no other reason than to set the voltage at which the diode conducts.
In the KB circuit it is R5, in the mixer supply, which is variable - again for the same reason.
The references that Lawrence quoted both explain what the diode does: it is just that, unusually, these sets have an adjustment for what, in other designs, is a fixed parameter.
