Color coding of tube amplifier wiring There is no official standard for this anywhere, so this here is just a good proposal. Also when building, you are going to see that you can't always do it 100% right as the number of available colors is not enough. Besides there is no need for a unique color scheme, since we usually ALREADY know we are working on DC heated filaments, just we don't know what is plus or minus. Also don't make an issue about two different colors connected together, this is normal. Mains General recommendations for wiring:
Mains Coloring In some countries the mains have one "hot" wire, which has the full mains voltage, and one "cold" wire which has zero Volts to ground, or just a few volts. In other countries the mains is symmetrical, meaning each wire has half the mains voltage, and each is 180° out of phase with the other. This will greatly improve the safety aspects, but it is more expensive. When wiring the mains part of the amplifier, you assume, one end of the inlet is "hot" and the other is "cold". Even when you have a symmetrical mains. Ssometimes curious hard to cure hum problems can be solved by reversing the mains plug. To have this option, you must wire the amplifier clean and tidy. Twist all mains wires, and make sure the current in each of the two is in opposite direction. This will greatly eliminate the radiated hum field.
Output transformer coloring This wire is often seen, but exceptions exist
Ground Path Truly specialist know how to make wiring without wasting too much wire, sometimes make small sins, that do not cause hum, to save wire and reduce the number of solder joints. Sometimes you have an old radio or music amplifier, and it is absolutely hum-free, and yet simple wiring, no chokes, and remarkable low power supply capacitors like 2uF only. This marks true designer art of the old days. If YOU try it, you may be disappointed. To prevent problems here are some rules of thumb: Do not fight hum with overly large capacitors. Sure voltage will be more stabile, the larger they are, but charge peaks are excessive, and will be terrified when you make those peaks visible on a scope. They are sharp, strong peaks and current shape is aggressive. So you solve one problem, and you get another. Better is to increase the choke value. That will also make the output voltage more stabile AND reduce current peaks. Even so, try to make the capacitors smaller, and the chokes accordingly larger. The silence of such a power supply will surprise you now. Also the rectifier tube will thank you with longest life. Use a single star grounding to the chassis, located at a position where signal is low. Alternatively, use or a fat (2mm) ground bar, which at first you wire independent of the chassis, and the amplifier should be able to work without a chassis ground. Since this bus bar carries the signal, and resistance must be low, the best is silver wire. We sell silver wire per meter. The price is not so exceptional, and compared to what you pay for good speaker connectors and other vital parts, this is a useful investment. So the ground bar is the artificial"chassis" to which you connect everything. Then after this is done, and it can work without a connection to the metal housing, you connect the metal bar to the metal housing with ONE wire only. This, wire is to even out any potential, but will not have a current flow. You should check this with an ohms meter, before you connect that wire, resistance must be endlessly high. This prevents a ground loop systematically. Amplifier coloring
Fusing Fuse the mains in the hot end (brown wire) before the switch. If the mains transformer is the main power user, this fuse is calculated to the mains transformer. Any smaller power users, such as switched AC to DC modules for heater supply, should be separately fused. Perhaps all together as a group. For simplicity you can take solderable fuses here, since likely the modules will not fail, and if they do they will not short. Do not connect a fuse directly to choke wires, or directly from the tube plate to the transformer. If you want to protect a tube, and you see no other way as to fuse it, , there are methods, but this is too much to explain here. Be aware you may never interrupt the current through a choke or output transformer, as the result will be leakage inside the windings. The last will be audible as crackle noise, or high frequency loss or power loss on one channel. |