[mikethedruid]

Two ways, one more accurate than the other. If there are no signs of a tube shield on the chassis for the RF, mixer-oscillator, or both if separate, IF, and detector-AVC tubes, then it probably wants metal tubes. The other way is to look at the schematic, and see if the shield pin is connected to chassis ground, or is used as a floating tie point. If a tie point, it uses GT, if tied to chassis it uses metal. Pin 1 is usually the shield pin in metal tubes. To be certain look at the data sheets for the tube number with and without the G or GT.