Weird B15NC mod--done by factory?

[ThunderBucker]

Thunderbucker here, working on Cataldo's B15, which went down with a shorted PT primary.  Ouch. While schematic searching, I found that it wasn't built according to any schematic I could find. Not even to the schematic pasted on the bottom of the amp. According to the schema on the amp, power supply filtering is done by a  40-40-20-20uf can cap with the first 40uf serving the 6L6s, 1Kohm later the next 40uf serves the screens, then the two 20s serve the preamp and phase splitter, respectively.

What's weird is that  Cataldo's has a 4 X 40uF 500V  can cap (huh, bet that's hard to find these days) and it's been rewired so that the 6L6s are served by 2-40s in parallel.  Since that leaves us one cap short for the various filtering apps, another discrete 20uF cap has been hand-added in to serve as one of the preamp filters.

Check out the pictures.  The first cap cap sections are jumped, then paralleled.  The added cap goes to the pads where one of the can cap sections would have attached, but there is no solder on that pad.  Was this done at the factory?

Odd.  And there is the question that 80uF (40X2) is more capacitance than the 5AR4 is rated for (unless the current draw is low, YMMV etc)

So now I'm hoping some expert will chime in and knowingly opine "Ah yes, that mod went in from October 13 1964 to January 15, 1965, caused by a massive fire at the capacitor factory that caused them to do a running mod....This makes this the most desirable and rare of all the B15NCs...."

[Aussie Mark]

Steve, the most informative audience to ask this one is in the Fliptop thread at TalkBass.  It's one of the few sensible threads over there .....

http://www.talkbass.com/forum/f15/jess-olivers-legacy-ampeg-portaflex-club-part-10-a-951349/index14.html

[ThunderBucker]

XLNT.....will give a try

[Psycho Bass Guy]

Lots of B-15N's left the factory with circuits that differed significantly from the published schematics and revisions. My '76 is cathode biased and came that way. My opinion is that the unskilled guys assembling the amps didn't have much oversight and if an amp passed QC without blowing up, it shipped. Given that it's a pretty conservative circuit in many ways, I think I have yet to find two wired completely identically, but most sound pretty similar. The supplies seem to be the biggest offenders, with weird filtering arrangements that ought to cook the 5AR4's but end up eating the PT.

[ThunderBucker]

Thanks for the help!  Well, 80uf is a bit much for the 5AR4, so I'm thinking about the recap kit from fliptops that adds a discrete 60 for cap #1, and then 40's in a can cap

http://www.fliptops.net/catalog/p-100023/cap-kit-for-ampeg-b15n-b18n-sb12-v.2-x-seriesamps