26-07-2026, 06:27 PM
(This post was last modified: 26-07-2026, 06:35 PM by Mike Watterson.)
It has to be a tungsten or halogen lamp.
It's handy if you are not sure.
For an ordinary valve radio or radio gram..
A 100W one is dim if it is maybe OK. It's bright if there is a fault. If it's a simple AM only radio with no dropper (AC only) then a 60W lamp may do.
It is simply in series with the live to the equipment.
Mains Live -- fuse---- lamp terminal O other lamp terminal ---- Radio live
Mains Neutral --------------------------------------------------------- Radio neutral
If it is bright and doesn't dim in a few seconds, then unplug and look for faults without the equipment plugged in.
Note no regular meter, even that measures capacitance will show a faulty capacitor that has high leakage, or breakdown on HT,
You absolutely can't use LED or CFL lights. It must have a filament. Tungsten (and halogens) are also a bit like barretters or current limiters as the resistance is 10x lower when cold. Hence far better than a variac if there is a fault.
Also a lamp limiter works on a SMPSU as there is a small voltage drop (nearly none on no load). OTOH a low voltage from a variac can destroy a SMPSU. Poorly designed ones burn out on "Brown outs" because if they are 45W output then at 200V in they take about 0.25A. Assuming about 90% efficient. At 240V 0.2A. But at 70V probably about 0.8A as efficiency drops. Some are 110V/240V and will cope for a while with 80V in. Others that are 220V to 240V may be shortlived at 80V in.
It's handy if you are not sure.
For an ordinary valve radio or radio gram..
A 100W one is dim if it is maybe OK. It's bright if there is a fault. If it's a simple AM only radio with no dropper (AC only) then a 60W lamp may do.
It is simply in series with the live to the equipment.
Mains Live -- fuse---- lamp terminal O other lamp terminal ---- Radio live
Mains Neutral --------------------------------------------------------- Radio neutral
If it is bright and doesn't dim in a few seconds, then unplug and look for faults without the equipment plugged in.
Note no regular meter, even that measures capacitance will show a faulty capacitor that has high leakage, or breakdown on HT,
You absolutely can't use LED or CFL lights. It must have a filament. Tungsten (and halogens) are also a bit like barretters or current limiters as the resistance is 10x lower when cold. Hence far better than a variac if there is a fault.
Also a lamp limiter works on a SMPSU as there is a small voltage drop (nearly none on no load). OTOH a low voltage from a variac can destroy a SMPSU. Poorly designed ones burn out on "Brown outs" because if they are 45W output then at 200V in they take about 0.25A. Assuming about 90% efficient. At 240V 0.2A. But at 70V probably about 0.8A as efficiency drops. Some are 110V/240V and will cope for a while with 80V in. Others that are 220V to 240V may be shortlived at 80V in.
