[time-nuts] Re: 5065A - Replacement of A14CR13 (Logic Ass:y) Thyristor "Continuous Operation" ?

[ed breya]

The CR13 can be almost any small SCR, like in a TO-92 size. I happen to 
know of one offhand, because I just yesterday used it in the Z3801A 
project, for the same type of function - latching the state of the 
indicator. I have a bunch of these in the thyristor department, and 
looked up various ones until I found this particular part was about right.

https://datasheetspdf.com/pdf-file/284595/UnisonicTechnologies/XL1225/1

This is an oldie. Another classic one is the C103 SCR. There should be 
plenty of modern little SCRs that will do. If nothing seems right, you 
can always make your own equivalent from a PNP and NPN Q tacked together 
right - but two parts are needed, and possibly an extra resistor or two, 
so it would be kind of a kludge.

For an SCR, the main things are gate current sensitivity, trip 
(latching) anode current, and holding current.

BTW in my Z3801A project, the SCR holds the "power on" state, but I 
drive the lamp the opposite way. It stays off in normal operation, and 
lights amber to warn that AC power has dropped out in the past - simply 
because I have plenty of a certain style amber lamps, but only one green 
(for lock). The reset button trips the SCR back on, and the light goes out.

I found the circuit wouldn't latch at first - I had made the anode 
current only about 1 mA, well above the holding current, but the trick 
is you need the available trip current to be high enough to go, then it 
holds down to much lower amounts. Changing to a smaller resistor made it 
work.

Ed