16-08-2026, 11:41 PM
Hi Peter,
I'm sure you'll get there
Noting you're using the US term ("Dim Bulb Tester"), if you haven't already, it might also be worth searching for "Lamp limiter", which I think is the more common term in the UK. That should bring in some more results.
You might have already seen it, but here's a really simple version: https://www.vintage-radio.com/projects/l...miter.html
And there is a very well documented build of that here on this very forum: https://golbornevintageradio.co.uk/forum...p?tid=4781
It's a good starting point. As you want to have multiple lamps of different powers, I'd just put them in series with the bypass switch across each. As mentioned, you probably can't make use of the neon bulb within, unless you think it might actually give you some useful information about the voltage seen at that point in the chain and Neutral.
Definitely carry the Earth across. On those occasions when you wish to use an isolation transformer (and you *know* why it's necessary), then I'd place it between the lamp limiter and the DUT. Remember that your RCD prior to this unit will no longer offer you protection on the output side of the transformer. For the transformer itself, do not carry the Earth through. You can read about transformers separately in this document: https://golbornevintageradio.co.uk/forum...?aid=11638
Not having the variac in the same box is a complication because, as mentioned, it means you'll need two mains inputs to get the meter powered. I know you've made the opening for it, but I'd be inclined to drop it as the variac markings will give you a close enough idea of the input voltage and the behaviour of the bulb will let you know what the load it doing. Obviously the rating of the selected bulb will give you a decent idea of the current flow. This is all quite imprecise in nature - the idea being to know when it's safe to skip the bulb once the basics of the DUT are established - so accurate current measurements are "nice to have" in a lamp limiter. More valuable on the variac itself, arguably.
Some of those voltage/current meters can be a bit sketchy - here's one that I tested and ended up modifying quite substantially: https://www.markhennessy.co.uk/mdu/
All the best,
Mark
I'm sure you'll get there
Noting you're using the US term ("Dim Bulb Tester"), if you haven't already, it might also be worth searching for "Lamp limiter", which I think is the more common term in the UK. That should bring in some more results.
You might have already seen it, but here's a really simple version: https://www.vintage-radio.com/projects/l...miter.html
And there is a very well documented build of that here on this very forum: https://golbornevintageradio.co.uk/forum...p?tid=4781
It's a good starting point. As you want to have multiple lamps of different powers, I'd just put them in series with the bypass switch across each. As mentioned, you probably can't make use of the neon bulb within, unless you think it might actually give you some useful information about the voltage seen at that point in the chain and Neutral.
Definitely carry the Earth across. On those occasions when you wish to use an isolation transformer (and you *know* why it's necessary), then I'd place it between the lamp limiter and the DUT. Remember that your RCD prior to this unit will no longer offer you protection on the output side of the transformer. For the transformer itself, do not carry the Earth through. You can read about transformers separately in this document: https://golbornevintageradio.co.uk/forum...?aid=11638
Not having the variac in the same box is a complication because, as mentioned, it means you'll need two mains inputs to get the meter powered. I know you've made the opening for it, but I'd be inclined to drop it as the variac markings will give you a close enough idea of the input voltage and the behaviour of the bulb will let you know what the load it doing. Obviously the rating of the selected bulb will give you a decent idea of the current flow. This is all quite imprecise in nature - the idea being to know when it's safe to skip the bulb once the basics of the DUT are established - so accurate current measurements are "nice to have" in a lamp limiter. More valuable on the variac itself, arguably.
Some of those voltage/current meters can be a bit sketchy - here's one that I tested and ended up modifying quite substantially: https://www.markhennessy.co.uk/mdu/
All the best,
Mark
