Trouble with PUT circuit experiments in Make: Electronics
I'm unconvinced by all the suggestions! The resistor values are not crucial, and the capacitor value can vary significantly. If the transistor isn't going through its negative phase and reaching the valley point, I'm betting the transistor is dead. Have you, by any chance, tested it?
I can't entirely check the circuit, because some leads are partially hidden. Would really be helpful to trim the leads and making everything easier to see.
The first edition of Make: Electronics was published almost 11 years ago, and I haven't received reports of this problem, so I think it has to be a component issue.
PS. Thanks for reading my book, and sorry you have this problem.