Help Fix My Modded Marshall

[braintheory]

So I just got another modded Marshall today (1979 2204 donor amp). It was sounding great, but I noticed only one of the 2 powertubes was lighting up and producing any heat I could feel, so I turned the amp off, inserted my bias probe between the sockets this time before turning it on again, no reading on either powertube and then noticed the 12AX7 at v3 was not lighting up either now, tried different tubes in that spot, still nothing, so I haven’t gotten sound out of it anymore. Wondering if you guys have any ideas to trouble shoot. Either way the guy is very sorry and will fully pay my tech to fix it if I can’t figure anything out here

 

[SpiderWars]

So I just got another modded Marshall today (1979 2204 donor amp). It was sounding great, but I noticed only one of the 2 powertubes was lighting up and producing any heat I could feel, so I turned the amp off, inserted my bias probe between the sockets this time before turning it on again, no reading on either powertube and then noticed the 12AX7 at v3 was not lighting up either now, tried different tubes in that spot, still nothing, so I haven’t gotten sound out of it anymore. Wondering if you guys have any ideas to trouble shoot. Either way the guy is very sorry and will fully pay my tech to fix it if I can’t figure anything out here

iSounds like something is up with the filaments. Hopefully just a bad connection. You could pull the offending tubes and inspect the metal 'clamps' inside the tube sockets to make sure they haven't been damaged. Check the filament wiring inside the amp.

Also make sure it isn't the tubes themselves. Seems very unlikely tho. Good luck.