Voltage conversion of Accuphase A-48

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.
 

Thank you very much, imhififan. I will appreciate very much if you would explain more about  'measuring voltages across large filter cap?'  What should I do concretely to measure voltages across large filter cap?

The purpose of voltage conversion from 100v to 120v is to give the amplifier circuitry correct operation voltages.

https://1.bp.blogspot.com/-Yn62ubWAJB8/XZBPQoN1Z8I/AAAAAAADXY8/Fa5bof2bzGs7ECGh9lAp1qj-ddhNSw6dwCLcB...
To measure voltages across large filter cap, use a DMM set to DC voltage measure voltage on 60000uF capacitor (RED probe on red wire connection, BLACK probe on the aluminum plate connection), you should get same or very close voltage reading by power up the A-48 with 100V mains voltage before conversion and power up the A-48 with 120V mains voltage after conversion.

BTW, I strongly recommend to use a Dim Bulb Tester to power up the amp at the first time after voltage conversion.
If anything goes wrong the light bulb will simply light up instead of dimming and save the amplifier from any damage.

Although the Dim Bulb Tester is a low tech simple circuit connecting an incandescent light bulb in series from the mains to the amplifier, it is an amazing device works as a current limiter. Every one should have one in their tool box!

I like your "Dim Bulb Tester” idea imhififan!

it will save thousands of $$ if wire - terminal connections are wrong

I am trying to convert an Accuphase A-48 from 100v to 120v as well. If anyone has a photo of the connections pre and post the conversion just like someone has posted, would be appreciated. Thanks.