Never replace a fuse with one that has a larger current rating than the amplifier calls for.
In the case of the Wurlitzer, you can still remove the lid and examine the fuse (although you must unplug the amp first and be sure to avoid touching any circuit components). In some amplifiers, for instance the 200 and 200a, the fuse is hardwired into the amplifier and must be replaced by a tech. The fuse is usually mounted somewhere around the power cord, inside a fuse holder with a plastic cover. But if the circuit experiences an inrush of excessive current, the wire inside the fuse will burn up and the amp will power off, just as if you’ve hit the switch. If the amp is working normally, the fuse completes the circuit like any other piece of wire. A fuse is a very thin piece of wire enclosed in glass. If the pilot light in your Wurlitzer 120 is not working, you should confirm that the power supply is working correctly, and all DC voltages are as expected.Īll amps, with the exception of some cheap and unsafe vintage models, have a mains fuse. For instance, in the Wurlitzer 120, the 120v pilot light is powered by the DC power supply which powers the tubes. Occasionally, the pilot light will be located somewhere else in the circuit. However, if your power transformer is working, your amp is officially on and you actually have a no-signal problem. Your question now: is the power transformer’s high-voltage secondary functional? (An easy test: are you getting the expected voltage from the high voltage secondary?) If not, your power transformer is malfunctioning and probably should be replaced. This means that everything on the primary side is probably more or less working fine, because pilot-light-approved amounts of voltage are being passed to the heater secondary winding. In a tube amp, on the secondary 6.3v winding of the power transformer.
For that reason, you can’t make too many assumptions from a working pilot light, and you should still confirm that the fuse is intact. In many vintage amplifiers, the pilot light even precedes the fuse. The circuitry following your pilot light, however, is a question mark. All wires leading up to your pilot light are probably in good shape too. Good news! You can safely deduce that your wall outlet is working. The primary side of the power transformer. In a vintage amp, the pilot light is usually found in one of two places: But which part of the circuit? It depends on where the pilot light is located. So, at least part of your circuit (granted, a very small part) is working fine.
However, if your pilot light is on, it means that you are successfully getting the appropriate voltage to your pilot light. If you are getting nothing from your pilot light, move on to the next section and check your fuse. However, if your amp is truly in abysmal condition, it is possible that your pilot light is broken and you also have an independent no-signal problem deeper in the circuit. The classic indication of a broken amp is a dark pilot light. It’s worth testing the amp in a different outlet before you start troubleshooting. But double-checking the outlet isn’t wishful thinking: it’s covering your bases. Basically, when the outlet fails, it is natural to scapegoat the gear instead. Outlets provide us with electricity and we barely have to think twice about it, whereas its a miracle that the 40+ year old amplifier plugged into it still exists, let alone turns on. A working wall outlet is a normal, everyday occurrence. The wall outlet is an important one to check. Is the amp plugged in? Are the tubes present? Is the speaker connected? Is the wall outlet working correctly? Steps to diagnosing an amp that doesn’t turn on
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