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...."
