>:: There are four TO3 transistors marked SGS 108-055

I suspect these may be selected for the OEM company. I know RCA used to do 
this, and that is how their range with just 5 digits came about, they were 
sub groups of a generic class like 2N3055, but selected for beta range or 
some other characteristic.

So for this particular use they may be a 2N3055 but selected for fT. The 
number on them is then probably the in house part number for the OEM 
company. 

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