Voltage conversion of Accuphase A-48

https://img.canuckaudiomart.com/uploads/large/466882-1b7bea05-accuphase_a46_class_a_power_amplifier....

Plug in the amp to the mains (120v), measure voltage across terminal 1 and 3, if the voltage reading 140v or more the amp is wired to 100v, if the voltage is about 100v the amp is wired to 120v.

To measure DC resistance, you need to pull out all transformer primary winding wires from the quick connect terminals, make sure all wires not touching each others, using a DMM to measure the following resistance:

white - orange = ? ohm
white - red = ? ohm
white - blue = ? ohm
white - black = ? ohm
white - yellow = ? ohm
white - brown = ? ohm
orange - red = ? ohm
orange - blue = ? ohm
orange - black = ? ohm
orange - yellow = ? ohm
orange - brown = ? ohm
black - red = ? ohm
black - blue = ? ohm
black - yellow = ? ohm
black - brown = ? ohm
yellow - red = ? ohm
yellow - blue = ? ohm
yellow - brown = ? ohm

Please report back the result and see if we can figure out which wires belong to the two sets of primary winding.

Below is the pictures of A-46 wiring:

https://img.canuckaudiomart.com/uploads/large/466882-1b7bea05-accuphase_a46_class_a_power_amplifier....

https://img.canuckaudiomart.com/uploads/large/466883-52355904-accuphase_a46_class_a_power_amplifier....

I tried to pull out all transformer primary winding wires from the quick connect terminals, but I could not pull them out since they are pushed into very tightly. Is there any way to pull them out easily? Or is it ok to pull them more strongly?

Below is a picture of A-48 wiring:

http://https//onedrive.live.com/?cid=6E164E2EDFDD40F6&id=6E164E2EDFDD40F6%2166335&parId=6E164E2EDFDD40F6%21120&o=OneUp

Below is the correct URL for A-48 wiring:

http://https//www.canuckaudiomart.com/view_userimages.php?user_id=175846

Sorry again. Below is the correct URL for A-48 wiring:

https://onedrive.live.com/?cid=6E164E2EDFDD40F6&id=6E164E2EDFDD40F6%2166335&parId=6E164E2EDFDD40F6%21120&o=OneUp

I tried to pull out all transformer primary winding wires from the quick connect terminals, but I could not pull them out since they are pushed into very tightly. Is there any way to pull them out easily? Or is it ok to pull them more strongly?

Use a pliers on the connector metal crimp to pull and a flat head screw driver push on the connector tip should be able to release the connector.

From the picture of A-48 wiring, as @westcoastaudiophile pointed out, the wiring scheme is the same as A-46, so I believe you can skip the resistance measurement, simply swap the black and brown wire, yellow and blue wire.
The new wiring diagram will be:

1= white+orange 2= red 3= yellow 4= blue+brown 5= black 6= none

It is very important to make sure no damage to the A-48 if wiring change is wrong! I strongly recommend to use a Dim Bulb Tester to power up the amp.

 https://www.youtube.com/watch?v=wRFRwOnLsZI&t=73s
 

to verify correct voltage can measure voltage on large capacitor terminals, which should be in a range 50V to 55V

As @westcoastaudiophil suggested,  measuring voltages across large filter cap is the most reliable way to be sure the conversion done right: power up the A-48 with 100V mains voltage before conversion and power up the A-48 with 120V mains voltage after conversion, the voltages across filter caps should measured about the same.