Remove tube and check the filament rings to ground; normally the Ohm meter will indicate zero Ohms. If the filament rings indicate an infinite resistance, check the following:
On FM-T transmitters manufactured before 2001, the fusible link F3 on the metering board (P/N 919-0048) may be open. On FM-T or FMi-T transmitters manufactured between 2001 to the present, the fusible link F3 on the PA current meter shunt (P/N 919-0048-xxx) may be open.
In either case, to get the TX back on the air, you can replace the fuseable link with #28 gauge buss wire. Then contact our Parts department (email@example.com) to order a replacement fusible link F3.