a GFA-7400 Voltage Conversion
The GFA-7400 amplifier is produced in both a 120VAC only version and a multivoltage (120VAC or 230VAC convertible) version. The version can usually be distinguished by external inspection. The 120VAC only version has a fixed AC line cord. The convertible version has a detachable line cord. Internally, their are two differences. The toroid transformer in the convertible version has 2 primaries; the first primary has a black and brown lead, the second primary has a black and brown lead with white stripe. The toroid transformer in the 120VAC only version has only the brown and black lead (1 primary winding). Additionally, the connecting block mounted next to the power switch is different in both versions. In the multivoltage unit, this connecting block has 5 pair of mounting leads (as is shown in the figures below). In the 120VAC only version, the connecting block has only 3 pairs of mounts. The conversion procedure for the multivoltage GFA-7400 unit is listed below.
Conversion of Multivoltage Units
120V to 230V 1. Unplug the amplifier and remove the top cover. 2. Locate the connecting block mounted next to the power switch. 3. Move the transformer leads so they are configured as shown in figure 1. 4. Remove heavy gauge wire connections between screw down portion of terminals. 4. Change the rear panel AC fuse from 12A to 6A, AGC. Place a sticker on the rear panel at the fuse holder to show the new value fuse (6A) and new value operating voltage (230VAC). 5. Test the unit with a 230VAC source.
Brown Black Brown/ White Black/ White
Figure 1: Transformer lead configuration for 230VAC operation (multivoltage units)
230V to 120V 1. Unplug the amplifier and remove the top cover. 2. Locate the connecting block mounted next to the power switch. 3. Move the transformer leads so they are configured as shown in figure 2. 4. Add heavy gauge wire between screw down portion of terminals as shown. 4. Change the rear panel AC fuse from 6A to 12A, AGC. Place a sticker on the rear panel at the fuse holder to show the new value fuse (12A) and new value operating voltage (120VAC). 5. Test the unit with a 120VAC source.

Brown Black

Brown/ White

Black/ White

Figure 2: Transformer lead configuration for 120VAC operation (multivoltage units)