Bend some sheet aluminum, drill some holes, and bam! Almost that simple. Making a chassis from scratch is your opportunity to make your amp construction convenient. Let’s make a chassis that requires no circuit boards. The main requirement for the layout is to keep AC away from DC. We also have to keep the transformers from coupling by placing the cores in different directions. Keep the heaters away from DC power, ground, and signal path. Now this chassis is ready to be knocked out!
The chassis above is a designed to be compact. One side for transformers, one side for tubes, and one side for controls. Facing the controls, the left side of the amp contains the AC. This is our chance to make the chassis convenient by placing our ac power cord, fuse, and power switch close together. Maintaining our AC left theme is our rectifier on the tube side. Bravo if you guessed the power transformer would be on the left too. Now we should have no issues keeping the AC away from the DC.
These transformer are linked here:
https://crunchytubeamps.com/product/35w-sec-voltage-220v-x2-6-3v-x2-r-core-transformer-2/
https://crunchytubeamps.com/product/5k-5w-single-ended-output-audio-transformer-with-4-or-8-ohm/
The power transformer is orientated to keep all the AC on the left side, and provide HV lines to the rectifier tube. Right next to power transformer is our output transformer. They can be in close proximity to each other; however, the transformer windings should be 90 degrees from each other to avoid coupling. I choose to place the output transformer in the middle. The length of the of the wires are perfect to reach our DC power and power output tube (also placed in the middle). We’ve sacrificed some space, but our leads can reach everything now.
A good option for the tubes is have all the heater terminals line up on the same side. In this case, I have the heaters opposite the control side. I need my ground, DC power, and signal to run on the control side. The heater wires are now conveniently isolated from the ground, DC voltage, and signal path. Our choices have been simple yet effective!
This was my first time using a 6N2 Chinese preamp tube, and I was pleasantly surprised at how quite it was compared to 6N2P Russian tube. I will use this tube again: https://crunchytubeamps.com/product/6n2-valve-vacuum-tube-replace-6h2n-6ax7-6av7-ecc41/
The right side is the only choice for the preamp having placed the rectifier closes the Power transformer and the power tube closes the output transformer. Magically, our tubes are now in perfect placement with our voltage drops. Every filter capacitor in our DC power path is in perfect line with the tube it provides power to. What are the chances?
This part requires passive components to be on hand. Use a resistor to measure the distance from the tube socket to the input. do the same with the control pots ensuring all components can reach their destination. I like to keep all my controls evenly spaced in line with each other. I like to use zip tie pads to hold everything in place, and keep components from reaching the chassis if needed.
We took sheet aluminum, bent it, drilled some holes, and now we have a chassis that requires no circuit boards. Didn’t even need hook up wire. Use this 1/16 aluminum for chassis material. Amazon has good deals on it.
