Old Analog Ammeter Model 448 Identification, Usage, and Testing Methods

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#1 21665727 05 Jan 2013 11:41

Josh Stein Josh Stein

Anonymous
Post #1
21665727 05 Jan 2013 11:41

Greetings all. I came across the following panel meter while going through some of my dad's old stuff. I was wondering if any of you could help me identify where it came from, what it would likely be used for ("To read VOLTS press Key"?) and if there is an easy way for me to test functionality.
For sense of scale, the front face is approx 9cm across.
Model number is listed as 448. Google has proved fruitless to date.
Thanks!
--J

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#2 21665728 05 Jan 2013 14:24

stephen Van Buskirk stephen Van Buskirk

Anonymous

Post #2
21665728 05 Jan 2013 14:24

I had an old military surplus meter similar to this. I figure it was used for a radio or some such connected to a battery. I expect that if it was for an engine with a built in charging system the ammeter would show -150A to 0 A to 150A.

If you check the meter resistance with an ommeter if it's open the meter's bad and if it has a very low resistance, possibly less than your metrer can read, then it has a shunt resistor, or it's toast.

My meter did not have a shunt resistor for the ammeter built in. I used a 5v power source with a potentiometer in series with the meter. I started with a very high resistance and reduced it until the meter read half scale. I then measured the voltage across the meter. I calculated the resistance that would give 50A at the voltage I measured using ohm's law (not a local ordinance). I made a resistor with that resistance, put in parallel with the meter and I had an ammeter.
In my case it was a very low resistance and I used a piece of copper wire. You can find tables with the resistance per foot for various wire gauges on the net.
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#3 21665729 05 Jan 2013 21:31

Mark Harrington Mark Harrington

Anonymous

Post #3
21665729 05 Jan 2013 21:31

Sounds really stupid its also possibly ex marconi marine surplus too

I remember my father had similar when i was much younger. Just before the dawn of the transistor in those days germanium, but as Steven pointed out you will possibly need a shunt across this in order for this to be usefull

But dont throw it away

Its probably got historic value to it Anyway I hate too see this go to waste

I personally love vintage electronics It has so much more character I catogorically refuse to part with old valves. I still keep a collection even to this day

Yes possibly to some people a little strange however I cant bare to see just how unapreciative the world has become when they simply smash an electronic master peace such as the thermionic valve because they want the metal Its as distastefull as burning the books contained in a libruary or a school

As much i find the so called digital age interesting I also know and appreciate just what this is doing

You might like to read this article in connection with the digital gap and education I hope some of you will

http://live.vodafone.co.uk/html/defaultx.aspx...fi=28&typxm=NewsPage&segitemid=09092011175353
#4 21665730 05 Jan 2013 22:03

Mark Harrington Mark Harrington

Anonymous

Post #4
21665730 05 Jan 2013 22:03

Whilst discussing books digital age education and vintage electronics Id thought I would share this with you No its not for sale The book is older than I am and was given to me by my Dad Its got some very interesting articles inside valve related These were the projects that they built when they were youngsters

see below
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#5 21665731 05 Jan 2013 22:23

Mark Harrington Mark Harrington

Anonymous

Post #5
21665731 05 Jan 2013 22:23

Books that you can never buy again for the love of money

Experiments we used to play with when we were young
Nostalgia
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#6 21665732 05 Jan 2013 23:08

Mark Harrington Mark Harrington

Anonymous

Post #6
21665732 05 Jan 2013 23:08

This is another component you will possibley never see again I thought Id show this as well still in mint condition

Mecury switch with real mercury encapulated in glass also with original bakelite insulators on braided copper Worth more than money could ever buy and has history A real story about development

See below for image I still kept it
#7 21665733 06 Jan 2013 00:15

Rodney Green Rodney Green

Anonymous

Post #7
21665733 06 Jan 2013 00:15

HI Josh.
I can clearly see a meter shunt on the back of the meter and it looks like a fairly high current shunt to me. Thus i suggest that the meter scale could be used to see the current range, which is likely to be still accurate if the meter movement is OK. I cannot read the scale from the photo but if it is linear (equal spaces between the readings) and the readings themselves are linear, such as 10, 20, 30, 40, etc then it is a moving coil meter. If the readings are not linear across the scale then it is a moving iron ammeter. If you remove the shunt (carefully) you could check that the movement itself is OK with an ohm meter as described in other reply. You are likely to see the meter needle move as well as see its resistance. Start reading on the high Ohm range of the multi-meter and look at the ammeter dial to make sure the movement of the needle is in the right direction. If not (going backward) reverse the connection of the Ohm meter. Remember to replace the shunt if you use it to measure the current indicated on the meter face or you will instantly and permanently destroy the movement.
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Topic summary

The discussion centers on identifying and testing an old analog panel meter, model 448, approximately 9 cm in diameter, found among vintage equipment. It is suggested the meter may be a military surplus or marine radio ammeter, possibly from Marconi, used to measure current in battery or engine charging systems. The meter likely requires a shunt resistor to extend its current range, as indicated by a visible shunt on the back. Testing involves measuring the meter coil resistance with an ohmmeter; an open circuit indicates a faulty meter, while very low resistance suggests the presence of a shunt or damage. Functional testing can be done by applying a low voltage source in series with a potentiometer to adjust current and observe needle deflection, then calculating the appropriate shunt resistor value using Ohm’s law to scale the meter for high current measurement. The meter movement type can be inferred from the scale linearity: linear scales indicate a moving coil meter, while nonlinear scales suggest a moving iron ammeter. The discussion also touches on the historical and collectible value of vintage electronic components such as thermionic valves and mercury switches with bakelite insulators.
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Old Analog Ammeter Model 448 Identification, Usage, and Testing Methods

Old Analog Ammeter Model 448 Identification, Usage, and Testing Methods

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