[R-390] Signal Increases With Limiter Switch

[keller family]

Some time ago, someone on the net suggested that if a nearly dead R-390A  showed an increase in signal strength by turning on and increasing the limiter switch, it was indicative of a specific problem that's easily corrected - a specific capacitor or something else that simple.  Does anyone recall that advice and what was it?
Thanks to all.
WB5KXO