me again with electrical question

[Texas_Ranger]

You can do that resistance test without shorting or disconnecting anything, it's called loop impedance test. You plug in a meter with a defined test load that measures the voltage at no load and under load. Since you know the current you can then calculate the resistance from the voltage difference using Ohm's law. You can perform that test both between live and neutral (mainly for finding bad connections) and between live and earth (ground) to make sure in case of a fault enough current can flow to trip a breaker/pop a fuse. The latter test is mandatory for any new/changed wiring in most European countries, as is a megger test. Switzerland even requires periodic testing (every ten years for homes).

By running around the house from outlet to outlet and measuring loop impedance you can spot weak connections, provided you have an idea where the circuits run (otherwise a sudden jump in resistance could just mean you found a socket connected to a different circuit with a lot more wire).

[phil]

Texas you are a wealth of information. I have heard of using shunts to check certain things but never really wrapped my head around it properly. I have an old resistance bridge that's probably from the "teens" that I think was used for testing in the early days. its quite nicely made with brass pins that you move to change the resistance. It was explained to me that in the early days they didn't' have meters for each use so they may have used a meter across it and the voltage drop would have given them enough to figure out the current etc. I guess that's basically how most meters work, by using a test resistor, the movement reads voltage but it's referencing the voltage drop over a test resistor contained in the meter.

I have capacitor checkers. One is quite a fancy and complicated one given me by an ex telephone company employee. I guess with some more expensive or hard to get at electrolytics they try to slowly increase voltage in an effort to "reform" them. the other tester just uses an eye tube to give an indication of leakage.
Often capacitors need to be checked for leakage under load so it'll test them at about 400 volts or so. Usually I just use the shotgun approach and replace all the capacitors except perhaps the really little ones in the picofarad range. the resistors fail a lot , they go higher with age usually and I replace the ones needed and keep the old ones if resistors measure within about 10% +/-.that's ok usually. In doing this work I will re-stuff the old cardboard tubes or the metal cans for the electrolytics. and use authentic looking wire and things to make it look as original as possible. when the radio is assembled you can't see the difference anyway because it's enclosed Many just don't worry about it. it depends on the rarity of the project.

in testing radio circuits you can't always check the voltage at the cathode as connecting the meter affects the circuit so I have often been told to use a resister on the end of the lead or to use a vacuum tube volt meter for this. I have one or two VTVM's I guess a scope can be used in the same way. If you just connect a normal multimeter to the set you can upset the signal path and the radio will stop playing.

some radios had a little battery to provide this small voltage difference and to repair these old batteries some find they can drill a little hole in them and wet them and they will spring back to life and others sometimes put a watch battery in there to replace them. they can keep their life so long beacuse they aren't really drained they just provide a difference in voltage.

some of the old radios have tubes with one volt filaments. they are very expensive to replace because of rarity. a used one that works is probably worth about $100 . sometimes people take a multimeter and try to check the filament and in doing so apply 9 volts (from the meter) and blow the filament. I guess that would be a place where you might use a shunt to see if you had continuity through the filament without applying over the 2 volts or so it takes to ruin the filament.

It would be a real niche business but it seems that someone could specialize in testing circuits in old buildings like this. it seems many electricians wouldn't know where to start with it, but it sounds like it's more common in Europe. .

Sometimes when we got new imported machinery we'd have to call in the guys from CSA ( equivalent of UL) to put their sticker on it and they might use a megger to check breakdown voltage before they put their sticker on it. the european electrical standards are usually quite high so I haven't seen too many issues. nowadays we get lots of made in china machinery and the switches and relays and other parts are so cheap they fail more often.

[GibsonGM]

I'm watching this conversation and enjoying it, lol.

Meter shunts: Read the section on shunts here, it's pretty basic (good!) and gets you up to speed. Knowing the resistance of the meter movement you're using is key, of course. You can get that with a DMM or by using a pot to send it to full-scale deflection, then calculate its resistance from Ohm's law
http://sound.whsites.net/articles/meters.htm#s4
The best part of this is that you can take a dead meter with a working movement and use it for something, which is far better than the dump


I have a movement from an old VTVM that I set up to do 100, 200....500mA, and is switched to then show 10, 20....100mA. VERY useful on the test bench, when the DMM is busy! I wire it into power busses going to projects, too, so I can see at a glance what's going on.

For a 1V filament, one could make a voltage divider and start off by sending only .5 or .75V to the filament....I can see where confusion on heater requirements could EASILY cause you to blow the thing, tho!! Everything I use is 12V or 6.3, generally speaking....

[Texas_Ranger]

I guess that's basically how most meters work, by using a test resistor, the movement reads voltage but it's referencing the voltage drop over a test resistor contained in the meter.

Yep, exactly! Although precision meters use a complex setup called a Wheatstone bridge, I think that's a network of four resistors, one of which is the one you want to measure. Been a while since I last had anything to do with them so my memory is quite rusty.

Shunts can also be used to measure large currents easily by inserting a resistor into the main circuit (i.e. in series with the load) and measuring the voltage drop across. If its resistance is much smaller than that of the load it'll only drop a small fraction of the voltage and only dissipate very little heat.

[phil]

thanks Gibson. the link is great. Ill read it over some more but I like that its pretty basic and understandable to me. Its so easy to get lost with electronics. I really only had a basic electronics night school course and have had to gather what I know just by fooling around and reading a bit. I got into tube radios about 15 years ago and for the first 5 or so I did a lot more but when I bought my house the radio restorations got put aside for house renos. I haven't lost interest and Ive got lots of neat projects I wan to look at.

I did restore one westinghouse columaire it looks like a grandfather clock. I have a couple more of those needing complete restoration. Ive got a Grunow Teledial 12 that I think will be a great radio and it has some neat history with shirly temple advertising it. evidently it has lots of tuning stages so should be quite selective.
these aren't mine but some links to similar ones. Just a few examples of the kind of stuff I like to work on.

heres the teledial http://radioattic.com/item.htm?radio=1110015
here's the columaire https://retrovoltage.com/2013/07/15/193 ... ock-radio/
here's a philco chairside radio again not my picture, but a sample. . I have one thats in nice shape but I think maybe someone else restored it. Im always scared to plug them in without opening them for a check of the wiring at least.
http://www.johnjeanantiqueradio.com/Philco370.jpg

I think I understand the basis of shunts but I need to try doing it more to get comfortable. as I think about this stuff I realize that it's been 10 years and my memory gets foggy so I should do more and try to get back up to speed a bit.

another thing I do is to plug my radios in through a clamp meter. The one I got came to me by luck as a hydro truck passed the other way and I spotted the meter drop out of the little door on the side of the truck and went bouncing down the busy road. I got it before it got run over but chasing down the hydro truck wasn't an option

That meter is for measuring higher amperage but I found I could make a coil with ten wraps around the clamp probes and one around my wire and I that multiplies the reading by 10 which gets me in about the right range. so if something is drawing too much I can spot the issue and hopefully unplug it fast enough

[Mick_VT]

This is so far that it might be considered at least the discussion is still electrical I guess

Do you need me to break this into a new topic?

[phil]

I suppose we should behave ourselves we are getting out of hand I'm probably the instigator as usual

[Mick_VT]

I suppose we should behave ourselves we are getting out of hand I'm probably the instigator as usual

LOL

Just having some fun with you guys but honestly wondering if I should split the topic

[phil]

mmccool719 hasn't responded since the original post but I am fine if you move it or delete some. we did steal the thread guilty as charged now we are going to get sentenced to some weekend paint scraping or something. maybe drywalling my living room ceiling will suffice? I started installing all the corner beads and taping. I must enjoy these things because I'm sure good at stretching them out. My contractor friend says I always start things and find harder ways and then do it that way. lol

[Mick_VT]

My contractor friend says I always start things and find harder ways and then do it that way. lol

I resemble that remark too!