How to Adjust the Bias on a Fender Super Champ
- 1
The trim pots on Fender amps are hard to access.amplifier image by Darko Draskovic from Fotolia.com
Turn off your amplifier and remove the power source. This amplifier carries potentially fatal current. If you have been using the amplifier, leave it for 10 minutes so that the tubes can cool down. Moving an amplifier while the tubes are still hot can cause the tubes to shatter. - 2). Unscrew the back of the amplifier. Unscrew the four screws on top of the Fender Super Champ that connect the cabinet to the chassis. Unplug the speaker wires; this is for added safety while you're handling the chassis. Next, remove the amplifier chassis by sliding it toward you. Some amplifiers have an external bias trim pot, which makes for easy bias adjustments. The Fender Super Champ's bias trim pot is located on the chassis.
- 3). Reconnect the speaker once you have access to the chassis. To check the bias, there needs to be a complete circuit in the amp.
- 4). Power up the amplifier. You need power running through the amp to measure the bias. It's imperative to exercise extreme caution from this stage on.
- 5). Connect the black wire from your voltmeter to the chassis. The chassis is grounded, so this is the safest place to do it. Be careful not to touch any other parts of the chassis.
- 6
Voltmeters are also called multimeters.multimeter image by Aleksey Bakaleev from Fotolia.com
Check the meter reading. A correctly biased Fender Super Champ should give a reading of 40 millivolts. Manually adjust the blue trim pot located on the right of the chassis to bias the amplifier tubes and check the reading again. It's a tricky process and usually takes a few attempts. The trim pot adjustments balance the current drawn by each tube so that they share equal load. If you find it impossible to get the bias to 40 millivolts, you may have a faulty or under-performing tube. If this is the case, disconnect the power, replace all the tubes and retry. - 7). Disconnect the voltmeter from the chassis and disconnect the speaker wire, then turn off the power. Slide the chassis back in place and reconnect the speaker wire. Screw in the four screws on the top of the cabinet.
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