Ampeg Jet mystery component

[Randall]

mid 60's Ampeg J-12t, all original, except for badly done switch replacement. Guy wants a cap job, new AC cord and to replace whatever it was that looks to be missing from the PS section of the board. He tells me he just bought it today, and played it at the guy's house. I flip it on in front of him and as he is telling me not to worry about powering it up... Crack!! Big spark coming from the either the cap can or the rectifier tube. Switch it off and drain the caps.

Now I don't think the missing part has anything to do with the spark, but I am going to re-cap it first. I cannot find a proper J-12T schematic that isn't from the 90's or a Joe Piazza variant. I am working off my own J-12D schematic. The two points in question are the bottom eyelet with the piece of leg sticking out, that goes to B+ (first cap and pin 8 of 5Y3) and also as you can see jumpers to the first big resistor (1k 10W). The top eyelet is ground, and you can see evidence of a leg broken or snipped off. The solder all looks original. Now the question is, what would have been in there going from B+ to ground? I don't see a thing anywhere on a schematic that would indicate it was designed in, whatever it was. Was this just another Ampeg ad-lib on the fly on the factory floor?




http://www.kbapps.com/audio/schemati...mages/j12d.gif

[Randall]

EDIT: OK, I think I know what is going on here. I spied a photo and a schematic of a 1964 J-12a, and it shows a 20uF/450v cap in that position. This amp has the original 4 tab can with 3 tabs at 20uF/450v and the fourth at 20uF/25v. So they put the fourth 20uF/450v on the board. Seems someone clipped it out in this case. I am going to put in a 4 tab 20/20/20/20@475v and put the 20/25v on the board. That makes more sense to me.