I had the same thing with My Marshall JCM 800 Lead Series Head and JCM 800 Lead 1960 cabinet running at 16 ohms.. Same thing happened twice, that PS1 got smoking hot. I surely don't want to burn up my Marshall so I unplugged it and it is just sitting there. I have seen an awful lot of comments with the same problem. I was in touch with the vendor (a very well known and reputable company) But the process is dragging out. Either return or replace. I don't believe I would purchase another one of these.. I also have been in the game for a while. Started playing at 12, 65 knw and still at it.I purchased a Bugera PS-1 100W attenuator and followed the instructions with proper functioning speaker cables and matched impedance @8ohms.
Sounded great for about 5 minutes, I let the 50W JCM900 4500 series warmup for about 20 minutes then started dialing in an awesome tone and I started smelling burning parts. I stopped playing and noticed the PS-1 was smoking just a little bit. Little smoke signals is the best way to describe it. I turned it off immediately. Is this a product error or are the JCM 900’s just not cut out for attenuators? Your thoughts please and thank you guys. I’m new by the way. Been playing since I was 13 and I’m 30 now.
Side note* Used a 4x12 Marshall cab 8ohms