Tubes Asylum Questions about tubes and gear that glows. FAQ

---

[ Follow Ups ] Thread: [ Display  All  Email ] [ Tubes Asylum ]

---

[ Alert Moderator ]

---

Re: Excess line voltage can kill an amp

Posted by Chris Haedt (A) on November 2, 2003 at 04:09:37

In Reply to: Re: Excess line voltage can kill an amp posted by koo on November 1, 2003 at 19:48:40:

Meter impedance refers to the load the meter will place on an AC circuit. With analog meters, this is usually referred to in ohms per volt. Older meters were typically rated at 1000 ohms per volt, while a more modern meter like a Simpson 260 is 20,000 ohms per volt on DC and 5000 ohms per volt on AC. This means that if you place the Simpson on the 250 VAC scale to measure line voltage, the load the meter will place on the circuit is 250 X 5000 ohms= 1,250,000 ohms. This would disturb some circuits, but I can assure you it will cause no sag in home wiring systems. The typical digital meter will have an impedance that is not scale dependant, and my Flukes are 10 megs. This means that my Fluke will present a load on a circuit of 10,000,000 ohms. The Simpson analog meter (on the 250 VAC scale) will load a circuit four times as much as the Fluke, but this is of no consequence when measuring home line voltage. I just measured 150 VAC from my power supply, with my Fluke 45 and four analog meters (Simpson 260, Triplett 630PLK, Triplett 630NA, and military ME-297). All meters were within a volt or each other. This is as it should be.

If I put a 10 meg resistor in series with the volt meter leads--THEN they would all read differently according to the impedance they presented to the circuit created.

500 volt caps are perfectly safe to use at 485 volts. The 500 is the working voltage that the cap can see continuously. This does not mean that the cap will fail if briefly exposed to higher voltage. After all--the original 500 volt caps are still good after 40+ years, and now I have reduced the input voltage by changing the primary on the transforer. I might add a surge resistor between the rectifier and the filter cap--but watching the voltage as the unit turns on--this does not really seem necessary.

This post is made possible by the generous support of people like you and our sponsors:

Sonic Craft

---

[ Top of Page ] [ Contact Us ] [ Support/Wish List ] [ Copyright © 2025, Audio Asylum, all rights reserved ]

---

[ General ] [ Speakers ] [ Tubes ] [ Vinyl ] [ Digital ] [ Hi-Rez ] [ Video Asylum ] [ Cables ] [ Tweaks/DIY ] [ Music ] [ Films ]

---