Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => AmpTools/Tech Tips => Topic started by: TubeGeek on June 14, 2009, 05:47:22 pm
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I have a small collection of vintage meters and recently I unpacked the box they have been in for five years and decided to try and use them. It is going to be a little project for me to build some kind of wood panel where I can mount these meters and label them so that when I am testing an amp I can monitor multiple voltage and current points simultaneously.
I have one thing called a Galvanometer...from what I read about this meter, I can't see a practical use for amp work, any ideas where/if I could use this thing?
http://www.glacieramps.com/Glacier_Amplification/Vintage_Meters.html
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(http://i40.tinypic.com/1zgci0k.jpg)
I happen to have just bought a 1963 catalog including Simpson's line. This object is listed as both a microammeter and as a galvanometer, part 1327C or 1329C depending on size.
A basic galvanometer is a compass with some turns of wire around it. It can read very small current, in either direction. A basic galvanometer is uncalibrated. It is excellent for showing small current, also to indicate zero current (exact equality of voltage potential). They were often built big enough for a whole classroom.
What do you do with it?
Connect to gitar pickup, wave a magnet slowly. The galvo needle will waggle. This shows how electromagnetic systems work.
Add a series resistance, it reads voltage. There are few uses for a zero-center voltmeter in gitar amp work; you could bridge it across push-pull cathode resistors to adjust bias-balance.
The meter sold for $18 back in 1963. I bet few survive. There are not many uses, but if someone today needed one, it ought to be worth $20.
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http://en.wikipedia.org/wiki/Galvanometer
Yes, they seem to show the existence, direction and amount of a small elec current. The amount may have accuracy issues.
They can show the presence of a tiny current in the human body, for example. I don't know what your 50 -0- 50 scale is: milli amps, micro amps? If the former it could measure curren in preamps. If the former, it could be fed current through a voltage divider to get measurements dwon to its level. Or it could just look cool on a shelf. Great collection!
EDIT -- URL fix -PRR
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And the real primary use for one, both in the old days and today, is to use the galvanometer in conjunction with a known voltage source and a few other pieces of test equipment to calibrate yet another meter.
When I say "known voltage source" I mean in the sense of an electrochemical cell that has an exact known voltage at a given temperature (usually somewhere in the neighborhood of a volt, but the cell is never exactly "1 volt").
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Unusual Meter--
I once took an old radio, that didn't have a dial--took an old backwards reading noise meter--Had a pot coupled to the tuning cap, Low dc voltage fed pot--Wiper voltage gave a reading number on the noise meter--had a chart with 4 numbers, my favorite stations--
a lot of work for a dial, huh!
Mackie2
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Thanks for the insight on this meter. It looks like it'll end up being a meter that will pretty much just sit around the shop unless one of you guys would like it?