Dim light bulb tester (UK) I’ve just changed all my electrolytic capacitors in my power amp and got myself a Variac and Dim Light bulb tester (100W bulb). I’m monitoring the B+ and as I increase the voltage the lamp begins to glow at about 115 volts on the Variac. I took my KT120 out leaving the other valves in (including PL519 voltage regulator tubes). I now go up to 140 volts on the Variac and the bulb begins to glow. The voltage reference tubes (regulator circuit) light up but not the one for the negative bias (which normally illuminated straight away under normal power up-but maybe not enough voltage to strike yet). So now I’m worried about stepping up the voltage anymore even though there’s no funny sounds or smells etc. I can’t believe anything is wrong as I’ve checked the capacitors so many times but don’t feel I can push it any further. Any help or experience in this much appreciated.

Although there are consequences if you connect an Electrolytic Capacitor in reverse in a circuit-does it harm the capacitor if you test it reversed with say a Fluke Multimeter on an Ohms scale?

Hi Folks, I’m in the process of changing all my electrolytics in my old UK Croft(RIP) preamp and power amps. They still sounded very good and quiet but I thought it prudent as most of them are over 35 years old 😬. Some of them did look a little tired although most seemed to test OK with a capacitance meter. The question I’m asking though is being that my setup is in my small bedroom, do I just go for switch on after replacing the Caps after triple checking I’ve connected them properly or is it prudent to cart the damn heavy power amp down the stairs and connect some speakers to it and power it up in the garden/yard 😁. I don’t have the luxury of a variac. I won’t hold anyone responsible for their thoughts 🙂.

Hi, I wonder if someone with this knowledge can help me? I’ve noticed on my tube preamplifier the designer has taken a wire from the casing of the small power transformer to one of the adjacent reservoir capacitor clamps. Presumably a handy place to pick up an Earth. Would this be for transformer screening or electrical protection as the transformer is suspended on rubber for anti-vibration purposes. Also that reservoir capacitor has half of its plastic insulation removed so that the clamp can earth its body. Its fellow reservoir capacitor also has half the plastic removed where it is clamped to the chassis. Is that for screening which I would have thought a little unusual? Any advice about this design feature would be much appreciated as I’m wondering if I need to remove the plastic coating when I replace the electrolytic? Thanks.