PDM12K40 is a transistor which comes in an uncommon TO-3 package which was used in many older applications such as pinball machines. DigiKey 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
Polarity: NPN
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: -
Package: TO3
Specifications taken from: https://alltransistors.com/transistor.php?transistor=44794
This option is in an active status and stocking at DigiKey. If there are any questions on this, please reply to this post and we will be happy to address them.
Please review the datasheets to ensure the alternative will work for your application.