The NCX-3 was pushing 100 watts input on AM (150 ma plate per instructions at 700 volts). Next project will be adding a fan. I'm still very surprised that the audio reports were so good for SSB with carrier but I typically get very good audio reports on SSB with the D-104. AM receive is narrow so I generally tune a little of frequency to reduce muffle.
I wouldn't run any more then about 25 or 30 watts carrier on AM, or in a short time, you can kiss your finals bye.
If I remember correctly, receive and transmit go through the SSB filter, so tuning off to the side is normal.