> felt that if I didn't understand ALL of the math
W.W.J.D?
This usually means the guy we are celebrating a birthday for next week. I would not presume to know what He would do. Anyway he didn't preach about amps.
No, I mean What Would Joseph Do? Joe the carpenter, dad to Christ.
We do not know a lot about Joe. He may have built temples or carved door-latches or pig-troughs.
We do know he did not have detailed Building Codes, span-tables, graded lumber. Math was right out: Roman numerals are way too awkward to multiply, He may have known other numbers, but he had no adding machine or calculator and his notepad was a stick in the dust. So no heavy computations.
BUT carpenters from before Joe to the present day do a LOT of their work by rule-of-thumb.
You want to put up a second floor or a roof. If you lay logs side by side, it may be strong, but that's a LOT of log. (And the mideast has been logged-out a very long time.)
A few large logs one way, then short logs or board crossways, is more economic. But how big?
The length of a beam (joist, rafter) can be about 15 times the vertical depth.
Today: my garage spans 12 feet, 144 inches. 144/15= 9.6 inches. Indeed we used "2x10"s which today are a shade over 9.0 inches. (We can run a bit shy because we buy graded lumber; Joe would be splitting trees and using knotty parts.)
The width of a beam, in residential work, about 1/10th of the spacing between beams. Today: 1.5 inch joists on 16 inch centers.
In heavy work (grain storage) you'd keep the depth about the same but double or triple the width. 9 or 10 inch deep by 3" or 4.5" wide joists on 16" centers.
A deeper joist is stronger and much stiffer BUT imagine a joist 18 inches deep and a half-inch wide. It wants to flop sideways. When you load it, it crumples. Showing that taking a good thing too far is bad. Basic carpenter thinking. (And not immediately obvious to a math-head.)
You can't walk on just beams, you need a solid floor. This is equivalent to "beams" as wide as the space between them. When beams are "over-wide" they can run about 20 or 30 times the depth. I have 0.5" flakeboard spanning 16", 32:1. If I used tree-wide boards (instead of 4x8 sheets) I'd use 3/4" boards, 21:1.
A short column's area can be 1/300 of the floor it supports. However NO stick in a frame can be more than 50 times its thin side, it will buckle under light load. (We propped a 100 inch rise with a 2x4, it buckled when Dana went upstairs.) If it has a heavy load, 1/20 is necessary. (Joe would use a 5x5; we have steel 16X stronger than wood so a 3" tube is ample despite 33:1 slenderness.)
And EVERYthing is approximate. If math-head calculates a 9.6"x 1.2" beam, buy a 2x12 (10.2"x1.5"). If you need at least a 2x3, but have lots of 2x6, use 2x6. A 26'x20' roof needs more than 520 square feet of cover (even if it were flat; mine is steep and took 22 4x8 sheets).
So... WWJD if he did tubes?
When you have a significant plate resistor, the cathode bias resistor is *about* Mu times less. 12AX7 with 100K in the plate, try a 1K cathode resistor. 12AU7 with 47K in plate, try 2.2K.
0.01uFd into 1Meg is 17Hz. From this you can estimate any RC filter just by pushing the decimal point around and then 2X or 5X shifts for 0.22 and 0.47 standard-values.
Topic: Merlin's preamp book in 2nd edition is out now (Read 8748 times)