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7 hours ago
Hi Guys
Japan is often left out of the discussion when designing PTs.
Japan nominally uses 100Vac mains, with some places having 200Vac. The widely used 100Vac is 15-20% lower than the typical North American mains, where PTs to match may be rated at 115Vac, 117Vac or 120Vac.
London Power always specifies PT primary windings to be 120V each, as this provides some protection against high mains situations. On the other hand, it makes it worse for use in Japan.
My later PTs accommodate Japan by providing taps on the primaries. The usual way to do this is to have identical primaries rated thusly:
PRI-1: BLK (120) - RED (100) - WHT (0)
PRI-2: BRN (120) - GRY (100) - ORG (0)
The above windings can be wired in many ways matching to 100V, 120V, 200V, 220V and 240V. Typically the manufacturer of the amp would make the interconnections appropriate to the designated sales region. If the amp was resold, say, and the new owner is in an area with a different mains voltage, the interconnections would have to be changed. To flip between the options using a single switch would require 4-poles and 5-positions.
To keep things simple for myself, I only wanted to match to 100V, 120V and 240V. Using the above windings would require a 4P3T switch. But I got lucky... I saw a schematic for a brilliant solution to this problem that only requires a 2P3T slide switch. I have not seen the original since and cannot remember who it was.
In any case, the solution requires asymmetric windings as so:
PRI-1: BLK (120) - RED (20) - WHT (0)
PRI-2: BRN (120) - GRY (100) - ORG (0)
The wiring is fairly simple. The slide switch has 4-pins per side (per pole). Designate one end to the 240V position. These end pins are linked together.
On one side of the switch the next pin is tied to BRN, then the third to LINE and the fourth to GRY.
On the other side of the switch the next pin ties to WHT, the third to Neutral, and the fourth to RED
As with all dual-primary PTs, LINE (L) ties to BLK through a fuse, and NEUTRAL (N) ties to ORG through a second fuse. The fuses are the same value.
With the above 2P3T slide switch wiring, one end is 240V, middle is 120V and the other end is 100V.
The usual 2-way range switch for 240V and 120V switches the BRN and WHT ends of the windings so the windings are in series or parallel.
Japan is often left out of the discussion when designing PTs.
Japan nominally uses 100Vac mains, with some places having 200Vac. The widely used 100Vac is 15-20% lower than the typical North American mains, where PTs to match may be rated at 115Vac, 117Vac or 120Vac.
London Power always specifies PT primary windings to be 120V each, as this provides some protection against high mains situations. On the other hand, it makes it worse for use in Japan.
My later PTs accommodate Japan by providing taps on the primaries. The usual way to do this is to have identical primaries rated thusly:
PRI-1: BLK (120) - RED (100) - WHT (0)
PRI-2: BRN (120) - GRY (100) - ORG (0)
The above windings can be wired in many ways matching to 100V, 120V, 200V, 220V and 240V. Typically the manufacturer of the amp would make the interconnections appropriate to the designated sales region. If the amp was resold, say, and the new owner is in an area with a different mains voltage, the interconnections would have to be changed. To flip between the options using a single switch would require 4-poles and 5-positions.
To keep things simple for myself, I only wanted to match to 100V, 120V and 240V. Using the above windings would require a 4P3T switch. But I got lucky... I saw a schematic for a brilliant solution to this problem that only requires a 2P3T slide switch. I have not seen the original since and cannot remember who it was.
In any case, the solution requires asymmetric windings as so:
PRI-1: BLK (120) - RED (20) - WHT (0)
PRI-2: BRN (120) - GRY (100) - ORG (0)
The wiring is fairly simple. The slide switch has 4-pins per side (per pole). Designate one end to the 240V position. These end pins are linked together.
On one side of the switch the next pin is tied to BRN, then the third to LINE and the fourth to GRY.
On the other side of the switch the next pin ties to WHT, the third to Neutral, and the fourth to RED
As with all dual-primary PTs, LINE (L) ties to BLK through a fuse, and NEUTRAL (N) ties to ORG through a second fuse. The fuses are the same value.
With the above 2P3T slide switch wiring, one end is 240V, middle is 120V and the other end is 100V.
The usual 2-way range switch for 240V and 120V switches the BRN and WHT ends of the windings so the windings are in series or parallel.
