Roberts R500 Missing Transistor

[AlanBeckett]

I fear David that the problem may be that the OP thinks that there will be an instant 'Fix' and when it's not forthcoming, or looks to be much more complex than they expected, they give up.
Of course, they may simply have gone on Holiday, or got someone local to sort it out. However, common courtesy would dictate that it's reported.

Alan

[Terry]

Assuming that the OP does return sometime, I note that all the discussion has been centred on AF117 problems whereas the OP says the missing transistor is an AF115.

Although all of these AF11x transistors share the same style of construction and the consequent problems, it would be misleading to infer that an AF117 is a replacement for an AF115.

It might work - it might not, so it is wrong to give a misleading impression.

No disrespect intended to anybody who has posted but it is easy, when discussing the AF117 series to simplify it to just AF117 in the knowledge that most people will know that what you are saying refers to others in the series as well. The problem is that the OP might not be "most" people ...

[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.

[Terry]

Further to Terry's comment a lower numbered device will normally replace a higher number one but not vice versa.

That is such a blindingly obvious way of putting it - so why didn't I  think of it ...???

[Mark Hennessy]

Perhaps we'd be better off saying "TO7", as it's the encapsulation that's the problem, and there are other transistors that share that package and that problem?

The tin whisker problem also shows up in TO1 devices like AC128s et al...