Is the amp making rumbling or glassy, high-pitched noises?Īn ‘Ove’ Glove or an everyday oven mitt is a handy tool for dampening hot preamp and power tubes to determine which is bad, as well as for removing them once you’ve isolated the offending valve. If replacing the output tubes has not alleviated the problem, re-install the original tubes and have the amp serviced by an experienced tech. If you replace the power tubes and notice lackluster performance, an increase in hum, or one or more tubes glowing exceptionally red, the amp will need to be serviced by an experienced tech, because more than likely the grid or screen-grid resistor(s) have failed. Some tube failure can cause internal components to fail. However, this unfortunately does not mean the amp has a clean bill of health. If this corrects the fuse-blowing issue, you’ve found the cause of the failure. If you suspect this is a problem, install the new fuse(s) and replace the full set of matched power tubes. This is an especially likely culprit if the fuse(s) failing is an HT or output fuse. If not, replace the original rectifier tube and continue troubleshooting. If it now functions properly, you’ve found the cause of the failure. (Side note: It’s a good idea to know what kind of rectifiers are used in all your amps and to keep one of each necessary type in your spares kit.) After you’ve located the rectifier, install a new fuse and a new rectifier tube and try the amp again.

To see if this is the case, locate the rectifier tube in the amp-it’s usually the tube closest to the mains (AC) transformer, and it’s typically a 5U4, 5Y3, 5AR4, GZ34, or 6X4. If your amp uses tube rectification in its power supply, a shorted rectifier tube can cause a fuse to repeatedly blow. In such a scenario, possible causes for repeated fuse failure could be:

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