Using a dim bulb tester

[z-adamson]

I have a dim bulb tester that I built and I am using it for the first time and I am trying to interperate the results.

The device in question draws 25 watts according to the back panel. As such, I am using a 25 watt bulb.

As I understand it, the bulb will go bright and stay bright in the event that there is a short in the power supply.

The bulb going dim means that the power supply within the device checks out good.

What about no illumination at all at the bulb yet the power-on indicator on the device is very dim?

 

[jheu02]

My assumption here is that you just missed the slight glow on itintial power up. the caps in your H/K725 in the power supply are 2 x 470uF and 2 x 330uF. There's not going to be a huge current drain to charge those to begin with. In large amps with capacitance in the 10s of thousands uF, the initial current drain to charge those is what is depicted by the bulb glowing briefly and then dimming once charged.

 

[RocketMonkey]

What about no illumination at all at the bulb yet the power-on indicator on the device is very dim?

The startup surge may or may not make the bulb light up brightly or at all. I use a variac to limit power and wattmeter to measure it so not much experience messing with the dim bulb.

How much voltage drop you get will depend on the unit and bulb you use. Measure the voltage across the transformer primary or perhaps easier the bulb for an idea how far below normal its running. Be aware that as the temperature of the filament rises its resistance will also (point being its not a normal linear response like a normal resistor, this is what makes it so usefull). So for instance if its running at 80% (of line voltage) at idle it should not be 80% with the amp running loads, current will heat the filament and thus increase the series resistance. Great for protection. I have no idea what the typical voltage reduction/drop accrost the bulb would be.