B-12N April 1961 prototype
B-12N April 1961 Prototype(top)
This is a spectacular prototype which is as rare as they come. The B-12N and the B-15N used the same amplifier, the cabinets differed.
Note the half moon shaped porting.
This design differs from that of the double baffle B-15.
This chassis layout is what the B-12N/B-15N would become. Note the jewel lamp in the top of the chassis and Narrow lexan plastic logo plate mounted on the tube cage.
Interesting tube lineup. On the left is the 5AR4 or 5U4GB tube rectifier followed by two 6L6GC power Tubes. In the B-15N, these are followed by three small signal Tubes. This amp has an extra tube. Also note that the electrolytic can power supply Capacitor that is normally seen on the far left where the tube rectifier is located is not present. All the capacitors are under the chassis. Also note that there are two pots on the back right side of the chassis. One is labeled balance, the other feedback. The final revision had a single heater Hum balance pot. The feedback pot could be a presence control. This feature is seen in some current guitar amps. It's purpose is to boost the upper-mid range frequencies to provide more presence. They may have been using it to determine the optimal feedback resistor value in the power amp. The final revision of the B-12N/B-15N had two jacks on the back, one labeled EXT AMP which is a pre-amp in / power amp out, the other jack is EXT SPKR which is for adding an extension 8 Ω speaker cabinet.
The slot in the chassis in front of the Sylvania tube is quite Narrow. They only had one lamp in this prototype, they widened the slot and added a second lamp in the final revision.
B-12N Cabinet Restoration(top)