The only help I can be is to tell you that the power tubes are a push-pull circuit, that the device only has a single power amplifier section. Best thing to do is to take all the tubes to a testing machine and see if they're all OK.
Easiest thing to do is to swap out the power tubes with another set that is known to be good, but if something up-circuit from the power tubes has caused them to blow then you might put the testing power tubes at risk.
In the old days you could go to the neighborhood drug store and test the tubes on a big ol' tester. Alas ... Do you know any places that have a tube tester?