I know the SWR and watt meter may not agree with this statement, but I would try this anyway.
Hook-up the Comet, put the tip (center lead) of the connector in the radio, but don't let any of the ground connection or collar touch the back of the radio. If it hears fine, you need to test your transmission line. I have experienced your symptoms many times over the years and found that there is a problem with the cable. Typically a full or partial short circuit in the connector during assembly, but also occasionally in the coax itself.
If you have an ohm meter, look for a short between the coax center and ground both while connected to the antenna and on its own. Also see if you can find someone with an antenna and coax analyzer.
That said, don't discount anything mbrun stated. That is all good info. I personally would start with testing the cable so you know you're not chasing a ghost while using his troubleshooting recommendations.