The often-told story: You do not want to know how the sausage is made. (The same goes for Haggis!) But today I thought I would share my process on how I convert schematics to Circuit Boards that will be cut on the CNC.
The process starts with two critical tools and those are the schematic and a piece of quad graph paper (.25X.25 squares).
BTW for those ever welded to Manhattan (sort of Ugly type) construction this same process works FB.
Our schematic in this case the 5894 RF amp has a lot of small parts that make up the total amp. In the old days this called for metal bashing, cutting holes in a chunk of aluminum and then finding all of those terminal strips. Lot of holes to be drilled and tons of nuts, washers and bolts!
A fundamental pre-cursor is to understand how the circuit works and to also be confident you have not built in some unwanted feedback loops when you make the layout.
The additional consideration is that this will be a compact sized amp and Circuit Boards facilitate cramming 5 pounds in a 2-pound bag.
I noted that the left side of the circuit was part of the Input, Screen Bias, and Cathode circuits. The right side is the output. The left side Circuit board will be vertical to conserve space and that also facilitates some shielding. There is also an awareness of my circuit board stock which is 4X6 inches. So, circuit layout is bounded by the material stock I have.
Initial squares layout.
The use of the graph paper not only lets you space things to fit real parts sizes but also yields the coordinates of the island squares that will be entered into the design program.
A first run at parts placement shows that the final design will need a few more extra island squares and some redesign to fit parts. Initially I missed that one of the resistors in the cathode is a 10K 10-watt job. Read this resistor needs some real estate on the board.
The design system I use is G Simple as I have used that for about 15 years. Carbide Create works too.
The last photo is the layout that will be used for the first prototype board. Connections to the circuit board will be via holes drilled in several of the pads and then wiring is fed from the insulated back side of the board to a specific pad and then to the socket or control. I am adding a 0-500 ma Cathode meter to the schematic.
Of note when transmitting the amp is turned on via the action of the two transistors which are a Darlington connected DC switch. There is a bit of a "sample and hold" circuitry to keep the amp turned on between syllables. But if you want to see the idling current without turning on the transmitter then the momentary switch shorts the Cathode to ground.
The max rating on the 5894 is 600 volts on the plate so the idling current is perhaps around 10 ma. My 500-ma meter might not see that low of a value. So, a meter change to a 0-200-ma might be needed. But this is recognized and on the list.
The final board size is 3" X 4".
This is a universal process good for all types of projects and I will soon cut the 1st prototype board. Recognizing this is an iterative process, it may need a few more changes before declaring a final configuration.
This is how the sausage was made.
73's
Pete N6QW