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Electronpusher0 · 12th Oct 2021, 1:10 pm

As Maarten suggests if the ac input providing the trigger is the same as the ac used to generate the +5v supply it depends on how you derive the +5 from the supply.
If you used a bridge rectifier then you will not have a reliable 0V reference for the trigger.
Half wave rectification would actually be better and short out the 1K resistor to the 0v.
Better yet a separate supply and make sure that one side of the ac used for trigger is connected to the psu 0V

Peter

12th Oct 2021, 1:10 pm	#12
Electronpusher0 Nonode Join Date: Jun 2016 Location: Bognor Regis, West Sussex, UK. Posts: 2,301	Re: Interesting Vintage TTL Logic IC Problem As Maarten suggests if the ac input providing the trigger is the same as the ac used to generate the +5v supply it depends on how you derive the +5 from the supply. If you used a bridge rectifier then you will not have a reliable 0V reference for the trigger. Half wave rectification would actually be better and short out the 1K resistor to the 0v. Better yet a separate supply and make sure that one side of the ac used for trigger is connected to the psu 0V Peter