Roberts R500 Missing Transistor

[ppppenguin]

Further to Terry's comment a lower numbered device will normally replace a higher number one but not vice versa. Hence an AF114 (the lowest number) will replace any of AF115, AF116, AF117. I'm guessing that they were all made on the same production line and the best ones selected to be AF114 etc.

The AF118 is an oddball device, used as a video amplifier in early transistorised TVs. Not really part of the same series.