[Collins] R388 Product detector mods

[Dr. Gerald N. Johnson, electrical engineer]

You have detectors with different gains. Sure the audio level will
change. You aren't using the diode detectors with BFO anymore, you are
using the product detector. You raise the product detector's gain by
raising the plate load resistance. You don't want the product detector
coupled tightly to the oscillator, it can inject enough signal to
modulate the oscillator. The oscillator input grid on the product
detector needs enough RF voltage to swing it good (as specified in the
tube data sheet) but no more. Gain of a mixer (which is what the product
detector is) does vary with injection voltage, up until a point.

Volume with AGC off is always greater than with AGC on. AGC can only
reduce the receiver gain. Distortion in the last IF stages should also
be lower with the AGC on. Have you aligned the detector IF transformer
to account for the new circuitry? New circuitry will change the gain of
that last IF stage.

Going into low frequency audio oscillation is a sign of a need for new
electrolytic filter and by pass capacitors. Called motor boating in the
ault days.

73, Jerry, K0CQ, Technical Advisor to the CRA

-- 
Entire content copyright Dr. Gerald N. Johnson, electrical engineer.
Reproduction by permission only.