Mesa Color Code Plate Current Values (420 vs 440)

[user 41014]

I have no idea where the amp lived but I can tell you, it had a very hard life. (1972). I was really afraid to throw the switch fearing it might catch fire LOL. That there is a perfect application for a 100W light bulb in circuit! LOL I offered to restore the amp both cosmetically and electrically but he said "just get it up and running. I'm using it as a gig amp!" Needless to say, the guy got his amp back and is happy as a gecko in paradise!

I've been meaning to make one of those current limiters ever since I saw Uncle Doug using one. Simple to build and use, a bright problem alert, and draws the current only when a problem requires its protection.

Everyone that works on amps to any degree should have one. I was thinking 200W bulb but either way it adds kid's gloves to a repair.

 

[Mile High Effects]

I made a couple charts of estimations of approximate plate dissipation at 470v, idle plate current, and Mesa Color codes for 25 and 30 watt tubes in NON Simul-Class Mesa amplifiers (Rectifiers and such).

As you’ll see below, I wouldn’t shoot for 70% plate dissipation. Mesa shoots for around 30-40%. I would never run a Mesa above 50% plate dissipation, but that’s just my opinion on staying in the safe zone. When the amp’s been running for a while and you’re cooking your tubes, it will run hotter.

25w
EL34: EL34, 6CA7, KT77
6L6: 6L6WGC, 5881WXT, 6Π3C-E
27% 14mA Red
33% 18mA Yellow
39% 21mA Green
45% 24mA Gray
51% 27mA Blue
57% 30mA White (too hot, was dropped)

30w
6L6: 6L6GC
27% 17mA Red
33% 21mA Yellow
39% 25mA Green
45% 29mA Gray
51% 33mA Blue
57% 36mA White (too hot, was dropped)