Quote:
Originally Posted by Michael Maurice
I successfully repaired the flip flops on these using BC547’s and BC327’s.
The BC327’s have a similar current rating to the AC128’s and are pin for pin compatible
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I'd have expected BC327s to be a good substitute in this application. I looked at the circuit and it only depends on the PNP polarity of the transistor, not the base-emitter voltage. The base-in-the-middle pinout makes it a very easy substitution.
A flip-flop fault could certainly cause your spurious recording lights problem. AC128s were once thought immune to Tin Whisker Syndrome, but apparently it just takes longer to show. Better to whip the lot out now than store up trouble for later.
As for why Philips used a germanium transistor: They were still making them in the 1970s, and they probably were cheaper than a similarly-rated silicon PNP transistor (it's harder to dope silicon to P-type than N-type; germanium is the opposite).