Hammond 278X 229VA 800V C.T. Plate & Filament Transformer

The 278X is a 229 VA high voltage and filament transformer with an 800V centre-tapped plate winding rated 230 mA, a 5V C.T. filament winding at 3A and a 6.3V C.T. filament winding at 6A. It is aimed at tube amplifier builders, restorers and OEM engineers who want plate, rectifier-heater and heater supplies from one enclosed transformer on a 115 VAC, 60 Hz line.

Mechanically, the 278X is an enclosed, 4 hole, chassis mount design in the vertical ("X") mounting style, with minimum 6" long leads. Ordering-table dimensions are A 3.13 in (80 mm), B 4.00 in (102 mm), C 3.81 in (97 mm), D 2.50 in (64 mm) and F 2.69 in (68 mm), and the mounting slots measure 0.20 x 0.38 in (5 x 10 mm). The shipping weight is 7.7 lbs (3.49 kg).

Hammond states that 200 Series units can be run full wave bridge or full wave C.T., use Class A insulation (105 degrees C), are Hi-Pot tested at 2,000V RMS and are CSA certified (209651). The part is listed as REACH compliant and RoHS compliant.

The 278X primary is rated 115 VAC, 60 Hz. Following the August 2009 primary-winding running change, the series notes describe White and Gray leads for 115 VAC input (tape the Black), or White and Black leads (tape the Gray) where roughly 125V line voltage pushes the secondary too high. Never connect power to both the Gray and Black wires, which the manufacturer warns will destroy the transformer.