Basic Turret Board Construction
- Mar 23, 2011
- in Guitar Kit Builder - Amplifiers
This tutorial will show you how to create your own turret board, to be used in building a guitar amplifier. I'll cover a procedure for cutting the G-10 circuit board material, drilling the holes and installing the turrets to build a complete custom electronic circuit board. Like most things, there are many different approaches to this, but this is how I do it and I hope this helps you get started on your first custom board.
WHAT IS A TURRET BOARD?
If you're not familiar with them, turret boards were the predecessor of today's printed circuit board and are a means of mounting electronic components in a rugged, reproducible and serviceable manner. A typical turret board uses a thin non-conductive board with metal turrets installed in a pattern to match the desired component electronic layout. Electronic components such as resistors and capacitors are installed between a set of turrets by either inserting the component lead in the turret hole, or by wrapping around the turret terminal. In both cases the lead is then soldered.
Photo 1 - Turret board without components installed
Today, turret boards are used primarily in hand-wired vacuum tube amplifiers built commercially or by hobbyists. This is often part of replicating a classic amplifier design but because it is also well-suited to building vacuum tube amplifiers.
Photo 2 - Turret board with components, installed in amp chassis
MATERIALS FOR TURRET BOARD CONSTRUCTION
For the circuit board material I use 1/8" thick Garolite, Grade G-10/FR4, a glass-cloth laminate with epoxy resin binder. This material is the flame-retardant version of standard G-10 Garolite. I purchase this in a 12" x 24" sheets from McMaster-Carr. A piece that size makes a lot of boards, but it also comes in a variety of precut sizes and colors. I use standardized turret terminals from Keystone Products, part #1540-4 (shown right). These terminals are manufactured of brass and are bright tin plated for excellent solderability. They are available from several vendors including Mouser and Hoffman Amps.
The procedures involved in making a turret board include cutting and drilling the Garolite G10 circuit board material, which is a high performance fiberglass composite. As such, you should use the safety precautions called for when working with fibrerglass materials, which according to Dupont, include the following:
- Prevent and avoid skin contact by wearing gloves, suits and boots as necessary, and dispose of these items or remove them for laundering at the end of the work day.
- Work in a well-ventilated area
- Wear a facemask respirator
- Eye glasses or goggles should be worn to prevent eye exposures
While this tutorial does not cover the design or layout of the amplifier, I do want to say here that you'll need a complete design of your turret board before you begin. This should include a 1:1 drawing showing the size of the board and the layout of the components and turrets. We'll use this (Photo 3) in a later step to drill the holes for our turrets.
Photo 3 - Our 1:1 drawing of the turret board design, with connections shown to other parts of the chassis
CUT TURRET BOARD TO SIZE
Our first step is to cut the turret board stock material to our needed size. I like to clamp the piece of G-10 down (Photo 4) to a good work surface, and put wide masking tape where the cut lines are to be drawn in pencil, then make the measurements and draw the cut lines (Photo 5).
Photo 4 - Clamp G10 stock to work surface
Photo 5 - Apply masking tape and then draw cut lines
This board is 2.75" X 7.5" for a 5F1 Champ amplifier variation. I cut the boards with a hand-held jig saw with a fine metal blade, and cut right through the tape (Photos 6 and 7). This Garolite material also cuts well in a band saw with a metal blade.
Photo 6 - Cut along lines with jig saw
Photo 7 - Cutting completed
DRILLING TURRET HOLES
The next step is to use the full size (1:1) layout drawing as a template for drilling the holes. I just fold it around the blank board and tape it securely from behind (Photo 8), then apply a layer of heavy clear packing tape (Photo 9) to prevent the paper template from shredding when drilling.
Photo 8 - Wrap and tape the 1:1 template around the G10 board
Photo 9 - Apply a layer of packing tape to keep template intact during drilling
A drill press is great for doing the drilling but it is not mandatory. If you drill by hand, just be sure to drill the holes vertically so that the turrets will stand straight up and not be leaning in every direction. The turrets require a 3/32" bit and Carbide is best for drilling through the G-10. (Photos 10 and 11)
Photo 10 - Ready to drill
Photo 11 - Drilling a hole through the template and board
After all the holes are drilled, remove the paper template. Remember to drill any other holes you may need for stand-offs or wire leads at this time so you won't be drilling into a board full of turrets later on.
TURRET STAKING TOOLS
Turrets are attached to the circuit board by being inserted through a hole in the board, and then flaring the board end of the turret with a staking tool. The tool for staking the turrets is very simple to make yourself. As shown in Photo 12 it is simply two bolts ¼" to 3/8" and a couple of nuts and washers.
Photo 12 - Staking tool details
Just mount one bolt through a block of wood, such as a 2x4, and drill a 1/8" hole in the top of the bolt to make the anvil. Cut the head off of the other bolt and grind one end to a 30-degree point. (Photos 13 and 14)
Photo 13 - Staking tools - flaring tool (above) and anvil (below)
Photo 14 - Underneath the anvil mounting block
Next, put the pointed staking tool in the drill press (Photo 15), which should be unplugged for safety). If you do not have a drill press, see discussion "If You Don't Have a Drill Press" at end of this tutorial.
Photo 15 - Mount pointed staking tool into drill chuck
Position the anvil beneath the pointed staking tool (Photo 16) and you are ready to start setting the turrets
Photo 16 - Staking tools in position and read to set turrets
SETTING THE TURRETS IN CIRCUIT BOARD
Gather your supply of turrets (Photo 17) and drilled circuit board (Photo 18) to begin setting turrets.
Photo 17 - Turrets ready for setting
Photo 18 - Drilled circuit board ready for turrets
First, place a turret in the hole in the anvil (Photos 19, 20 and 21).
Photo 19 - Insert turret in hole in anvil
Photo 20 - Close-up of anvil with turret inserted
Photo 21 - Ready to stake the first turret
To stake turrets, align a circuit board hole over the turret in the anvil and press it downward. Be sure that the back side of the circuit board is facing up (Photo 22) so that the turrets are on the correct (component) side of the board.
Photo 22 - Turret inserted in circuit board, before staking
Now flare the bottom of the turret with the pointed staking tool in the press (Photos 23 and 24).
Photo 23 - Flare the turret bottom with pointed staking tool
Photo 24 - Flared turret
Continue one at a time until all of the turrets are set and staked (Photos 25 and 26). At this point you're done, you've completed your first turret board - congratulations!
Photo 25 - A row of staked turrets
Photo 26 - All turrets completed
If You Do Not Have A Drill Press
If you don't have a drill press, the basic procedure is the same to a point but you may need an extra pair of hands to help hold the circuit board steady. Place the anvil on a hard surface, such as a concrete floor, and gently tap the turret with the staking tool using a small hammer. Pay attention to the force used and be careful not to over do it. The flared turret should look similar to the photo in Photo 24. Please feel free to post any questions here as comments and I'll be happy to reply. Have fun with your amplifier projects and please work safely!