[skyscraper]

Using the pinout here: http://www.radiomuseum.org/tubes/tube_84.html you can test for a heater cathode short by measuring resistance from pins 1 or 5 to 4.

When the 84 is pulled and radio is unplugged, check the resistance between 2 and 3 of its socket. It should be about 350 ohms. If all the other tubes are heating and the transformer isn't getting overly hot, it is probably good. There are only two windings.