If you heard a loud "POP!" when you keyed the radio with the new finals, I'll be surprised if you don't find the plate choke exploded or burned, and a burned resistor or three under the socket of one or both final tubes. A tiny epoxy-coated RF choke that feeds the lower lug of the big plate choke typically gets croaked as well.
Turns out that 6146B tubes made in Owensboro by GE, or "6146W" types from that same factory have a stability problem in the Kenwood 520/820 radios. They spontaneously burst into high-level oscillation and draw all the current the power supply can deliver until the fuse trips. This surge of plate current is what overheats and damages the plate chokes and cathode resistors. Happens too fast for you to react and unkey in time to prevent damage. By the time that "POP!" sound reaches your ears it's already too late.
Never have found a cure for this. Tubes built by RCA and/or the Sylvania (says Phillips ECG) don't seem to exhibit this bad habit.
Otherwise perfectly-good government-surplus "6146W" tubes made in the 80s came from both vendors. The ones built by GE are toxic for this type radio.
Learned this lesson the old-fashioned way. Not a cheap one to learn, since the tubes typically suffer damage as well as the radio.
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