Remember that the light bulb is in series with ONE of the AC line wires.
It is NOT in parallel with the AC line (like normal). See this diagram:
https://antiqueradio.org/art/DimbulbSketch.jpg
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That diagram is a bit too ambiguous and incomplete, so stay with the first one.
Technically, the black (hot) lead should be the one with the switch and light bulb.
The other lead (white) is the neutral.
If you have a 3 wire IEC socket on the power supply, the safety ground is
carried through as normal, just the same as the neutral wire is.
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Between the two I found the first one more ambiguous - which was hot and what was occurring at the plug - so ended up building the one I showed you. It looked like the neater package. What might be a simple way of testing this thing?
Don't plug either end of the tester into anything.
Install the bulb. If there is a switch in the tester, turn it on.
Use an ohm meter across the wide blade (neutral) and narrow blade (hot) of the tester plug.
This should be an open circuit.
Same between the wide blade and safety ground.
Same between the narrow blade and safety ground.
Now measure ohms from the wide blade to the wide receptacle in the socket end.
Should be a short.
Now measure ohms from the narrow blade to the narrow receptacle in the socket end.
Should be around 10 ohms (the light bulb cold resistance).
If it's an open circuit, the bulb may be bad, or the switch may be off.
Now measure ohms from safety ground pin to safety ground receptacle in the socket end.
Should be a short.
If it passes these tests, it should be ok.
Okay then. The bulb lit up for a sec and then dimmed right out. The resistors for the LEDs on the PSU showed up so I installed them earlier. ... one of them has chosen not to light up. At this stage I guess we can take the light bulb tester out of the circuit?
I have 24.9 out of the V+ / GND and 25 out of GND3 / V-.
I have 24.9 out of the V+ / GND and 25 out of GND3 / V-.
You may have that LED in backwards. Is it reversed compared to the other side?
I may indeed! I will check it tomorrow. Getting to be a pain to pull that board in and out now. Thx for the hint.
You don't have to remove the board, the flat side of the LED is the cathode, which should go to ground.
You don't have to remove the board. The flat side of the LED is the cathode,
which should go to ground.
But I will have to pull it to remove / replace the LED. Which should be a fine pain in the butt.
But first determine what the problem is.
See if LED is in the right polarity, and measure the resistor.
If the LED is reversed, there will be 25V across it,
since no current flows in the series resistor.
If your DVM has a diode test function, it can light up the LED,
if the positive meter lead is on the LED's anode.
See? Besides just getting to put together a great amp, I get to learn things. Thanks so much for your help! Will test this out tonight.
The LED was in backwards. Tough little sucker to get out of there as well. Ended up breaking it so I could work one lead out at a time.
So I see I've essentially stepped into jakesnake1's thread on his build. I will create my own now and post some pics. I have pretty much everything to finish as well as some questions of course. Thanks for your help here rayma.
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