Vox VT-50 Repair

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Around the lab, we like to use a Vox VT-50 amp to try out our designs. It's a cheap, mostly solid-state amp that nobody will miss if something goes horribly wrong. This example has had a hard life, being dragged out to gigs and from workshop to workshop over the years, and recently developed a problem - sound was heavily distorted and intermittent. It was time to open it up and take a look inside.

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The VT-50 comes apart fairly easily. Like most guitar amps it's fairly easy to service. The VT-50 is somewhat unique as it's part of Vox's Valvetronix line - using a valve in the preamp stage for more "genuine" tone. The power amp is solid state, however. IMG_20141026_134632_053

The first stop was the input board. The main jack tore pads off the input PCB during disassembly. This is a poor design - a chassis mount jack wired to the main board would have been more expensive and time consuming to build, but more reliable over time. PCB mounted jacks often suffer problems with pads pulling off the board over time. This was fixed up, however the problem continued.

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The true culprit in this case was the main solid state amplifier chip, seen here mounted to the heatsink in the center of the photo. One of the legs had broken and was making intermittent contact with the solder pad on the bottom of the board. A small length of a component lead was inserted into the hole, reinforcing the leg and was soldered between the pad and the chip. Since then the amplifier has been running nicely!