Yet another B15 question

[sedan_dad]

Such a simple amp causeing so many questions.
What do the different desinations indicate?
B-15N , B-15-NC , B15ND - B15Nf
Mine is the B15Nf.
O.K. I give up. What does the f mean?

 

[Rob Mancini]

The different designations designate small changes in the circuitry or whatever. They don't stand for anything usually. I think the B-15S stands for "solid state rectifier" but that's about it.

The F used two fixed bias 6L6GC's, which gave it 30w according to the book, and it was the first single baffle cab design.

 

[whacker]

The "S" is a completely different amp than the "N", as far as power output and size. It's a 60 watter, and much larger overall. I don't think it existed until the late '60s/early '70s, so it has that cosmetic look to it. Main thing being it's larger and more powerful.

 

[WovenGraphite]

Get the book, you'll know all about it (p68 to 72).
(p71 and 72 can be read online, the google book scan has those two pages, here)
Then page 198 you have a picture of all Portaflexes... cute!


Quickly:

1960: B15, pre+split 3x6SL7, output 2x6L6GC, rect. 5U4GB, Jensen P15N speaker
8 months later apperance of B15N, same as B15 but with circuit redesign, each channel has own controls, choice of alnico or ceramic Jensen speaker.

1962: B-15NB, classic blue checker tolex, switch to solid state rectifier, claim of a 25W amp, then option of JBL D-130F speaker

1964: B-15NC, appearance of the first printed circuit board, back to tube rectifier with 5AR4

1965: the CTS square magnet 15" speaker is introduced
mid '65, B-15NF, new PCB layout, fixed bias on the 6L6GC, bumped power to 30W (oooohooooo! )

1967: B-15NF is now wearing black vinyl

B-15NC is a column type cabinet ("C" like column) with two 15" speakers
B-15ND has a matching extension cab
Both NC and ND are using the B-18 circuit with the 7027A power tubes.

Finally, 1968, the preamp section is changed but it stays a B-15N.


There are other details like capacitor and resistor value changes (listed in the book) probably irrelevant for this thread, this amp's history is fascinating...

Hope this helps!