I would ask your father if it has been serviced ? If the 4 Sony and 4 Toshiba transistors are on separate channels, doing the same thing within the circuit, I would assume it has been serviced, and the Sony transistors were no longer available to the servicer. Sony transistors and Toshiba transistors might measure the same, but many feel ( as I ), that they can sound different, given everything else is identical. If it is 2 Sony and 2 Toshiba per each channel, this might be either or, as Liz indicated.
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TA-F808ES uses both S & T type mosfets, so i believe the unit is still in factory state. Do not change unless you have the confirmation that amp was serviced and mosfets were changed. If in doubt check following site: https://audio-heritage.jp/SONY-ESPRIT/amp/ta-f555esj.html
In Japan it was sold under F555ES name.