Board Details
Notes and photos from Mitch about how he builds the amps.

Assembling the circuit board is usually the first step in building an amp. The key to a successful build is to have a good layout drawing for the board as well as the chassis and its wiring. These drawings are made from the schematic diagram. The components are placed in a logical fashion on the layout drawing, keeping in mind the rules for building an amp that's free from hum or oscillation. For example, don't run wires parallel to each other if they carry different signals, keep sensitive preamp components away from high voltage, AC and output components, and keep heater wires well away from everything else.

These amps use circuit boards similar to the ones used in the better amps built back in the 1950's and 1960's. They are more rugged than the circuit boards commonly used today. They are made from 1/8" fiberglass rather than the more common 1/16" thickness. They also use metal pins called turrets or metal rings called eyelets to hold the components and wires.

Today's printed circuit boards use thin copper foil laminateded to the fiberglass for the wiring. The components and wires are soldered to these traces. With the boards I use, the turrets or eyelets are mounted to the boards with a secure mechanical connection. The components and wires are soldered to the turrets or eyelets. Everything is connected together with 20 gauge wire rather than thin copper foil as used on printed circuit boards.

Not only is this more rugged than today's printed circuits, but it's easier to make changes to the wiring if modifications need to be done to the amps in the future. It's fairly common to modify a guitar amp to get different tone and it's a lot easier to make changes on a turret board than a printed circuit board.

Once a full-size layout drawing for the board is prepared, it's used as a template to drill holes in the board for the turrets or eyelets. The turrets or eyelets are pressed into the holes and secured in place by flattening the bottom with special tools similar to the way rivets are set.

Here's a picture of an eyelet board before assembly and all the components that will go on it.

Aberdeen Eyelet Board

This is the top of the board from the Custom 50 amp. The the resistors, capacitors and wires are all soldered to turrets.

Custom 50 Turret Board

Here's the bottom of that board. Wires can be soldered to the bottom of a turret, too. Some of these wires join various turrets together mainly to form power and ground busses. Others will be later connected to the potentiometers and tube sockets.

Custom 50

Eyelets are similar to turrets but you can't wrap a wire around them and they don't raise the parts off the board. Here's an example of an eyelet board from from the Aberdeen amp.

Aberdeen Eyelet Board

Aberdeen Eyelet Board

The wires that leave the board are called flyoffs. These can be attached either to the top or bottom of the turrets or eyelets. I prefer to attach them to the bottom. It looks neater. It makes it a bit harder to trace wires after the amp is built, though. Also the wires have to be roughly measured for length and attached as the board is built because the bottom can't be accessed once the board is installed in the chassis.

I start assembling the board by placing all the underside wiring. Then I work from left to right placing the components and flyoff wires. Once all the components for a turret or eyelet are in place, I solder the connection.

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