Varian Herley-AMT RF Dual Band Power Amplifier 6-500 MHz 3900C-12 Unity NMR. Pulled from a decommissioned Varian Unity NMR system in good condition. Varian Herley-AMT RF Dual Band Power Amplifier 6-500 MHz 3900C-12 Unity NMR Pulled from a decommissioned Varian Unity NMR system in good condition.