The Furuno FAR-2127 uses the MAF1565N (cross-reference NJT1565) magnetron, expected life 8,000–10,000 hours. Confirm the fault with a calibrated output power test before replacement — a reconditioned complete transceiver is often better value than a magnetron-only swap on high-hour units.
MAF1565N — also supplied as JRC part number NJT1565. The FAR-2117 uses the different MG5436 tube; the two are not interchangeable.
Above roughly 40,000 total hours, when modulator HV components and fan are also due for service. A reconditioned transceiver resets the whole TX chain and ships ex-stock.