PDM12K40 is a transistor which comes in an uncommon TO-3 package which was used in many older applications such as pinball machines. Digi-Key carries options to replace these.
2N3771G is a replacement which would be recommended specifically for PDM12K40. This is an upgrade with a 30A collector current capacity.
Type Designator: PMD12K40
Material of Transistor: Si
Maximum Collector Power Dissipation (Pc): 100 W
Maximum Collector-Base Voltage |Vcb|: 40 V
Maximum Collector-Emitter Voltage |Vce|: 40 V
Maximum Emitter-Base Voltage |Veb|: 5 V
Maximum Collector Current |Ic max|: 8 A
Max. Operating Junction Temperature (Tj): 200 °C
Forward Current Transfer Ratio (hFE), MIN: 10000
Noise Figure, dB: -
Specifications taken from: https://alltransistors.com/transistor.php?transistor=44794
This option is in an active status and stocking at Digi-Key. If there are any questions on this, please reply to this post and we will be happy to address them.