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If you can find one today even a 100 watt light bulb has an internal resistance of over 140 ohms when lit. It's not unlikely to have 100 watts worth of bleeder resistors in the amplifier alone. It probably won't bring the voltage up high enough to spot things like a leaky filter cap or diode in the string. Although, if the bulb stays at fulbrightness, you likely have a dead short that would have popped the fuse anyway.

In my mind the amplifier is already being questioned as a basket case so, I wouldn't be afraid to let the smoke out of some 50-year-old rectifiers or capacitors. That's not likely to happen through a 10 Ohm resistor either and, I just won't hang my head over the cabinet during initial power up. I'd probably pull the tubes on initial power up and check them for broken grid wires sorting to the anode, if I didn't have a tube tester. Then if a problem only happens when the tubes are installed, I know we have an internal voltage breakdown problem within one of the tubes.

Don't get me wrong, I like the light bulb test for many smaller pieces of equipment, I just find it problematic to obtain reliable results on tube amplifiers with large wattage bleeder resistors.

<blockquote data-quote="Shockwave" data-source="post: 844704" data-attributes="member: 10882">If you can find one today even a 100 watt light bulb has an internal resistance of over 140 ohms when lit. It&#039;s not unlikely to have 100 watts worth of bleeder resistors in the amplifier alone. It probably won&#039;t bring the voltage up high enough to spot things like a leaky filter cap or diode in the string. Although, if the bulb stays at fulbrightness, you likely have a dead short that would have popped the fuse anyway.In my mind the amplifier is already being questioned as a basket case so, I wouldn&#039;t be afraid to let the smoke out of some 50-year-old rectifiers or capacitors. That&#039;s not likely to happen through a 10 Ohm resistor either and, I just won&#039;t hang my head over the cabinet during initial power up. I&#039;d probably pull the tubes on initial power up and check them for broken grid wires sorting to the anode, if I didn&#039;t have a tube tester. Then if a problem only happens when the tubes are installed, I know we have an internal voltage breakdown problem within one of the tubes.Don&#039;t get me wrong, I like the light bulb test for many smaller pieces of equipment, I just find it problematic to obtain reliable results on tube amplifiers with large wattage bleeder resistors.</blockquote>

[QUOTE="Shockwave, post: 844704, member: 10882"] If you can find one today even a 100 watt light bulb has an internal resistance of over 140 ohms when lit. It's not unlikely to have 100 watts worth of bleeder resistors in the amplifier alone. It probably won't bring the voltage up high enough to spot things like a leaky filter cap or diode in the string. Although, if the bulb stays at fulbrightness, you likely have a dead short that would have popped the fuse anyway. In my mind the amplifier is already being questioned as a basket case so, I wouldn't be afraid to let the smoke out of some 50-year-old rectifiers or capacitors. That's not likely to happen through a 10 Ohm resistor either and, I just won't hang my head over the cabinet during initial power up. I'd probably pull the tubes on initial power up and check them for broken grid wires sorting to the anode, if I didn't have a tube tester. Then if a problem only happens when the tubes are installed, I know we have an internal voltage breakdown problem within one of the tubes. Don't get me wrong, I like the light bulb test for many smaller pieces of equipment, I just find it problematic to obtain reliable results on tube amplifiers with large wattage bleeder resistors. [/QUOTE]

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