Well I was just a tad bit bored today so decided to do a bleeder resistor modification on my Astron VS-70M AP. Astron meters lights whether led or older incandescent have a bad habit of burning out even with a resistor to drop voltage/current. They start burning out at about 5-6 months sometime less. They sell replacement light boards but I find it much easier to just replace the entire meter although much more costly than just the light board. Unfortunately the meter housings are enclosed so a small string of leds or single leds can’t be used as in an Ameritron amplifier meters which are clear on top.
The Astron voltage across the capacitors when energized is 22.60 volts DC. Total capacitance is 128000 uF. Decided to run with what I had on hand which was 1 watt 2.2k ohm resistors. Two were run in parallel giving a total resistance of 1.1k ohms and wattage rating of 2 watts. Installed a 5mm white led without the dropping resistor. This gives a nice visual when the lid is off or through the vents on the cover. Total voltage going to the led was measured at 2.98 volts. Didn’t measure current as the mod had already been performed and I didn’t want to un-solder the work already performed.
Running the power supply for a couple of hours resulted in the bleeders only being slightly warm to the touch.
After 15 minutes voltage has dropped to 3.39 DC and led voltage is 2.6 DC
After 30 minutes voltage has dropped to 2.68 DC and led voltage is 2.5 DC
The capacitors can now be safely shorted without any sparks/arc to bring voltage down to zero.
The reason for this modification is that many many years ago I did a meter replacement on an old Astron VS-50M. One of the wires when un-soldered touch something else and sparked resulting in the voltage regulator needing replacement. Through subsequent testing I realized that even though the meter read zero volts and there was no voltage on the output terminals that the capacitors retained their charge for a very long time…months. (128000 uF is a LOT) So even though one might assume having been off for so long it was safe to work around the inside this definitely isn’t the case. Also taught me never trust any capacitor to be discharged despite what the meters on the equipment say. Can you say “chicken stick” is your very good friend!
Yes Astron’s wiring definitely could use some serious improvement.
That’s all folks
Brad
KE0XS
South of Pittsburgh
The Astron voltage across the capacitors when energized is 22.60 volts DC. Total capacitance is 128000 uF. Decided to run with what I had on hand which was 1 watt 2.2k ohm resistors. Two were run in parallel giving a total resistance of 1.1k ohms and wattage rating of 2 watts. Installed a 5mm white led without the dropping resistor. This gives a nice visual when the lid is off or through the vents on the cover. Total voltage going to the led was measured at 2.98 volts. Didn’t measure current as the mod had already been performed and I didn’t want to un-solder the work already performed.
Running the power supply for a couple of hours resulted in the bleeders only being slightly warm to the touch.
After 15 minutes voltage has dropped to 3.39 DC and led voltage is 2.6 DC
After 30 minutes voltage has dropped to 2.68 DC and led voltage is 2.5 DC
The capacitors can now be safely shorted without any sparks/arc to bring voltage down to zero.
The reason for this modification is that many many years ago I did a meter replacement on an old Astron VS-50M. One of the wires when un-soldered touch something else and sparked resulting in the voltage regulator needing replacement. Through subsequent testing I realized that even though the meter read zero volts and there was no voltage on the output terminals that the capacitors retained their charge for a very long time…months. (128000 uF is a LOT) So even though one might assume having been off for so long it was safe to work around the inside this definitely isn’t the case. Also taught me never trust any capacitor to be discharged despite what the meters on the equipment say. Can you say “chicken stick” is your very good friend!
Yes Astron’s wiring definitely could use some serious improvement.
That’s all folks
Brad
KE0XS
South of Pittsburgh