Very Cool Vintage Ampeg B-15-N rolled in for some TLC... Pic Heavy!!!

DeafDave2 said:
The 6A fuse is internal and not accessible from outside the chassis. It is in series with the regular 3A fuse in case somebody puts a way oversized fuse in the fuse holder or wraps a piece of chewing gum foil around a blown fuse. The internal 6A fuse is much larger than the 3A fuse so that the 6A one won't blow before the 3A one. It is internal because if a 6A fuse blows, then something catastrophic has happened with a possible fire hazard and the user cannot easily over ride this fuse and he will be forced to open up the amp. The internal fuse is not in a fuse holder making it difficult to use the chewing gum trick.
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That makes sense. If it was for the AC outlet the schematic would have to be:

A8DCFACB-3E38-450D-BF60-7EBAA5D5D662.jpeg
 
My attempt to update the 1974 drawn schematic to 1976. No polarity switch and no second .047/600 cap. The fuses and power switch were moved to the black "Hot" line...:
b15n ac power 1976.JPG
 
I have a decent stash of those 5881/6L6WGC's, so I took a random sample of ten units and put 478V on the plates, 471V on the screens, and -51V on g1. I got an average plate current of 27.1mA, a high of 32.8mA, and a low of 21.2mA. These tubes are NOS from the nineties (I'm the original owner) and haven't been abused like some others that I have.
 
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