Josh Homme and band mates in front of an Ampeg VT-40.
The Ampeg VT-40 is an instrument amplifier, suitable for both bass and guitar. It is a 60-watt, stereo configured, two-channel amplifier. If your VT-40 isn't performing at its best, troubleshooting will determine the nature, location and severity of the problem. This saves you from unnecessarily dismantling the amplifier. It also enables you to inform any repair professionals of the nature of the problem, for a quicker fix.
Instructions
1. Push the power adapter plug into the socket on the rear, to make sure the connection is sound. Turn on the amplifier, but leave the Standby switch in the downward position. If the power light fails to illuminate, the problem is located between the mains input and the power transformer, possibly a shorted fuse in the power supply. The power transformer is located next to the mains input, on the chassis inside the amplifier cabinet. Replace the fuse and retest. If the power light comes on, but there is no sound, the problem may be with the power transformer, for example a shorted primary winding. This is a problem best tackled by a qualified electrician.
2. Flick the Standby switch upward. This delivers the full current to the power and preamp tubes. When not engaged, the tubes receive an attenuated current, sufficient to heat the filament of the tube. The tubes need to be warm before the full current is delivered. This ensures that the tube heating process is gradual, rather than sudden. Let the amplifier heat up for 20 seconds. Observe both the tubes. If they are glowing, this is a sign that they are in good order. If one or both isn't glowing, remove and replace with 7027-type tubes.
3. Pull gently on the speaker cable on the rear of the amplifier to check the connection. If the amp is powering up and the tubes are glowing but there is still no sound, a loose speaker cable may be the problem. If the cable is loose, reattach it to the socket.
4. Plug in a brand new guitar cable. The sound of a faulty guitar cable can often be mistaken for amp problems. Use a brand new cable to eliminate time-wasting investigations into crackling caused by a faulty cable. Turn the volume dial to approximately 1 or 2 and hit a chord. Let it ring out. If there is a flapping sound as the notes decay, this is a sign of a rip in the speaker.
5. Turn off the amplifier and remove the power adapter. Unscrew the eight screws attaching it to the cabinet. Slide out the amplifier chassis and inspect the circuit board. Look for fuses, resistors and transistors that have a sooty or discolored appearance. One blown board-mount component can cause the entire amplifier to fail. If you spot any but are unsure of replace it, refer it to a qualified tech.
6. Check the heat sink. The heat sink is the grille mounted on the rear of the cabinet. It dissipates the heat from inside the amplifier. Turn the amplifier on and leave it for an hour or so. If it remains switched on, the heat sink is functioning well. If it cuts out after around 10 minutes, it's possible that the heat sink isn't working and the amplifier is over-heating. An over-heated amplifier also gives off a burning smell. If you suspect yours is faulty, remove the rear cabinet panel and check that the heat sink is firmly connected to the chassis. If not, tighten the screws mounting it inside the cabinet so it sits flush against the chassis.
Tips Warnings
Wear latex gloves to handle the replacement tubes. This prevents oil from your skin contaminating the glass, which leads to hot spots forming on the surface.
Tags: troubleshoot, ampeg, heat sink, power transformer, Turn amplifier, Ampeg VT-40, amplifier also, amplifier leave, full current, guitar cable, inside amplifier, mains input, power adapter
