Power Transformer specs

If they were made specifically for Pioneer you may have more difficulty getting a data sheet than with their standard products. STK modules in general have never been too awfully reliable, regardless of what type or if they are abused or not. Their physical construction inside leaves a lot to be desired. That heat sink does look plenty big enough to go mounting a standard amplifier to, or to even make home-made modules to fit. Maybe not 5 of them, but two for sure.
 
If they were made specifically for Pioneer you may have more difficulty getting a data sheet than with their standard products. STK modules in general have never been too awfully reliable, regardless of what type or if they are abused or not. Their physical construction inside leaves a lot to be desired. That heat sink does look plenty big enough to go mounting a standard amplifier to, or to even make home-made modules to fit. Maybe not 5 of them, but two for sure.
I do have the actual service manual for the receiver that the transformer came from, and harvested the modules, relays, etc etc that I thought were worth it.
 
That should give you enough information about the transformer, as different windings were used for different parts of the unit...the pre amp and tuner would be around 12 to 15 V, with a few hundred mA for that.
The power amp section would be at the voltage and current needed for the amp modules, which to me look like custom printed STKs.
In any case, if you reduce the expected load by 20 to 25%, you will not overload the unit.
STKs were Class AB I think, not H.
Oddly enough, it seems the OEM STKs were simply marked Stereo Amplifier (or other function, they were in a lot of TV SMPS controllers etc.) and model number, the Sanyo mark was used only for open market units.
 
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I re-checked the voltage readings for the main amp windings.
They are not as pictures previously, but this photo is an update.
Apparently, the 50V windings are a just tad more than 1/2 the 100V winding.
See photo.
 

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