Must measure the DC voltage across the big filter capacitors and don't Must do any repair work inside the amplifier chassis you Limiter then plug the amp into the limiter and plug the limiter into the variac. Light bulb limiter will make the initial startup safer than starting the ampįuse, smoke or arcing will let you know there is a problem during each of the Video for how the light bulb will behave with a normal amp:įollowing the startup procedure below will help you locate a short.
#TRICKY TEST 2 HELP JACK TURN ON THE LIGHT BULB FREE#
See how the light bulb lights with a normal, problem free amp. If possible you should plug in a functioning amp to If the light bulb glows near its rated brightness there is a short Pretty bright when the amp is first powered up but then it will dim The limiter's light bulb will initially glow Short in the amp from pulling too much current and blowing a fuse or possibly doing damage This isn't necessary but if you have a variac you shouldīulb current limiter to keep an accidental Variac which allows me to slowly bring up voltage to the amp as the newĮlectrolytic caps form.
Indentation on the + end of the cap and the arrow pointing to the - end.Īmp has any diodes installed, such as a solid state rectifier or fixed biasĬircuit, make sure their polarity is correct-the striped Getting any of this wrong can lead toĮxploding capacitors and damaged transformers. If your amp has a fixed bias circuit make sure its bias filter cap(s) are connected + to ground because Cap &Īdding power be sure and verify the filter caps are connected - to The ground prong wire bolted directly to the chassis. Power cord wiring: Hot to the fuse, Neutral to the power transformer primary and You don't have continuity use your meter's continuity function to verify your You must not power up the amp until you have safety groundĬontinuity between the power cord ground prong, guitar cable sleeve, speakerĬable sleeve and chassis because the amp is a deadly shock hazard without it. If your amp has speaker wires one or both of them should show continuity with the Your amp has a main speaker jack, plug a cable in and test again for continuityīetween the cable sleeve and power cord ground Have continuity between the amp's power cord ground prong and (the part that isn't the tip) and the amp's power cord ground prong. Plug a guitar cable into an input jack andĬheck that you have continuity (meter "beep") between the guitar cable's sleeve Recommend you use a color chart and verify the value of every resistor in theīefore adding power to a new amp be sure and verify the Resistors are also common and can create very difficult to diagnose symptoms. To have unsoldered joints or missing wires or even components. Taking this last step can save you from hours ofįrustration as you try to locate a problem. Printed copy of the layout and highlight every wire and component as youĬheck them. Newly built or highly modified amp I highly recommend going through the entire amp with a Use just one hand when working on a powered amp. Lethal shock can run between your arms through your heart. Never touch theĪmplifier chassis with one hand while probing with the other hand because a High voltage then have an amp technician service your amp. If you have not been trained to work with Tube amplifier chassis contains lethal high voltage even when unplugged-sometimes Mistake and help with fault identification. Using the following procedure can minimize damage to the amp from a wiring Powering up a new, modified or heavily repaired amplifier is always exciting but Have comments or corrections? Email rob at: robinette at
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