A company called Kenetek in Lexington, KY is currently producing what it calls drop-in replacements for the T4-C. They also offer to re-build original T4-Cs. I have an unused spare T4-C; I tested it and with it in-circuit, using a sinewave tone, I get RMS limiting long before any peak limiting reading. With the old one in place, both types of limiting occur about the same time. I suspect my old one is wearing down and becoming sluggish with RMS limiting. Several years ago I modified my T/R relay system to disable audio feeding the limiter when not in TX mode, since shack noise and audio from the receiver were constantly driving the BL-40 into RMS limiting, thus causing unnecessary wear on the T4-C. Last night I checked the audio output section of the BL-40 and both output transistors, the U05 and U55 are practically dead-shorted from emitter to collector, measuring between 1.5 and 3 ohms with the ohmmeter in either polarity. Tested them in-circuit, then removed them and tested the naked transistors, same result. Q7,8 and 9 seem OK, checking the base-emitter and base-collector junctions with a Fluke digital multi-meter in diode test mode. Before dropping in new output transistors, I need to run some more tests, since something had to have caused both transistors to fail simultaneously and I wouldn't want to send a new pair into instant meltdown the first time I turn it on. I prefer to get this thing running to replacing the audio processor, because it so well maintains optimum audio level with my voice with little overshoot and no audible artefacts. Listening on the receiver, without the BL-40, my audio appears tinny and anæmic by comparison.