Build an 8.2 Ohm/110W Dummy Load for testing, or servicing guitar amps.

[DrNomis_44]

Update:

Well, I've finally finished building the new 8.2 Ohm/110W Dummy Load I've been working on, and here are a few pics so you can see how I went about building it:



I mounted all of the 22 180 Ohm/5W ceramic resistors on two 8-way tagstrips, making three groups of six resistors and one group of four resistors, all the resistors were soldered in parallel with each other, each group of resistors were wired so that all of the 22 resistors were wired in parallel, making a single 8.2Ohm/110W resistor, I used my multimeter to check the total resistance and it actually-did measure spot-on at 8.2 Ohms, which is pretty much near-enough to perfect as I'm ever going to get it .2 of an Ohm is about the resistance of a standard multimeter lead anyway, so I'm happy with it.



Another top-view pic.



A pic of the front panel showing the two terminal posts, the two terminal posts have small holes drilled through them, so, to attach a scope probe, you can use two short pieces of tinned copper wire, the earth clip of the scope probe goes to the black terminal, and the tip of the scope probe goes to the red terminal, this way you can use one channel of your scope to monitor the output of the amp you're working on, and the other scope channel to monitor signals at various points in the amp's circuitry, note that the Dummy Load will work with both solid-state and tube amps up to 110W in power output, so you can connect the Dummy Load up to say a 5W single-ended tube amp, like a Fender 5E3 with no problems at all, as long as the output transformer is set-up for an 8 Ohms speaker load.

Note: If you want, or need to build a 4Ohm Dummy Load, all you need to do is double the number of 180Ohm/5W ceramic resistors needed, so 44 180 Ohm/5W resistors all wired up in parallel should give you a 4.1Ohm/220W Dummy Load, if you make two 8.2 Ohm/110W Dummy Loads and wire them in series, you will get a 16.4Ohm/110W Dummy Load, which should be fine for testing/servicing say a vintage Marshall Super Lead Plexi amplifier.