The BBQ reference goes back to a "difference of opinion" between the other (Ted) BBQ and the 18watt.com group.
It transforms to BBQ because the largest maker of charcoal grills in the US has the same name as these guys, hence "BBQ"
The Morgan Jones books are very technical and aimed more towards the stereo music amp type on amplifier.
The Gerald BBQ books have a lot of info, tend to repeat themselves a bit and have some questionable info such as his suggestion for large caps before the rectifier tube as you were wondering about.
I would suggest "The Guitar Amp Handbook" by Dave Hunter, walks through a number of guitar amplifier circuits explaining what the components do and lots of pictures of classic amp internal to show the wiring.
Hope this helps