26-07-2026, 03:51 PM
Most of the LED panel meters are DC, common OV and need a separate 5V PSU if the voltage is more than 10 or 12V.
You don't need more than one bulb, especially with a variac.
You are best to replace all paper dielectric caps and test leakage / reform PSU electrolytics with a current limited bench PSU before applying any mains. Then generally only a valve TV needs a variac or a lamp limiter. I needed a lamp limiter once for a series AC/DC radiogram. That's in nearly 300 repairs/restores of mains valve gear.
Back in 1970s (and maybe earlier) people relied on a fuse after checking the obvious things first and rarely had a lamp limiter or variac.
Unscrewing / unplugging a lamp does the opposite of by-pass. It removes the power! You bypass the lamp with a switch.
Also never step up a SMPSU gradually as current is excessive!
A variac is rarely needed.
I'm wondering how & what sort of mains gear you intend to repair / restore.
You don't need more than one bulb, especially with a variac.
You are best to replace all paper dielectric caps and test leakage / reform PSU electrolytics with a current limited bench PSU before applying any mains. Then generally only a valve TV needs a variac or a lamp limiter. I needed a lamp limiter once for a series AC/DC radiogram. That's in nearly 300 repairs/restores of mains valve gear.
Back in 1970s (and maybe earlier) people relied on a fuse after checking the obvious things first and rarely had a lamp limiter or variac.
Unscrewing / unplugging a lamp does the opposite of by-pass. It removes the power! You bypass the lamp with a switch.
Also never step up a SMPSU gradually as current is excessive!
A variac is rarely needed.
I'm wondering how & what sort of mains gear you intend to repair / restore.
