Discussion in 'General Electronics Chat' started by EXG, Jul 3, 2009.

1. ### EXG Thread Starter New Member

Jul 3, 2009
8
0
I ruined my digital meter so I took out an old Simpson 260 analog meter and there is one thing I just cannot figure out. Al I want to do is check the currant on my amplifier so I can bias it. The currant I am looking for should read between 25 and 35 ma. If I set my selector on my meter to 100ma, which scale should I read. The scales are 0-10,0-50, and 0-250 dc. The currant selector is 100ma,10ma,1ma. Thanks Emmanuel

2. ### beenthere Retired Moderator

Apr 20, 2004
15,808
294
You read on the 0 - 10 scale. Just pretend it's 0 - 100.

3. ### SgtWookie Expert

Jul 17, 2007
22,199
1,801
There were a number of different series of meters.

Be careful to start reading current on a higher scale setting than you expect, or you may blow the internal fuse - or the meter for that matter.
For example:
Start using the 500mA range. Read the value on the 0-50 DC scale, multiply the result by 10.
If your reading on the 0-50 scale is less than 10 (indicating 100mA) then switch to the 100mA range.
In the 100mA range, you read from the 0-10 DC range, and multiply the result times 10 to obtain 0 to 100mA.

Tips:
Rest the meter flat on it's back while taking measurements; this minimizes the effects of gravity on the D'Arsonval meter movement.
Use the screw slot at the pivot point of the needle to adjust the needles' zero.
Look straight down at the meter with one eye when taking your reading. If you see the reflection of the needle in the curved mirror, adjust your head position so that you can no longer see the backside of the needle. This helps eliminate parallax error while taking the reading.

You are generally much better off to derive current measurements by measuring the voltage across a known resistance. I=E/R, or Current = Voltage/Resistance. This greatly reduces the chance that you will reduce your meter to a smoking pile of rubble.

For example, if your tube has a resistor from the cathode to ground that measures 100 Ohms, and you read 3v from ground to the tubes' cathode, then 3V/100 Ohms = 0.03A = 30mA.

4. ### EXG Thread Starter New Member

Jul 3, 2009
8
0
Thanks to SgtWookie and beenthere. You gave me the answer I was looking for and I also liked the download information for my Simpson. I can now continue on my project with confidence. Once again thank you for your help and information. Emmanuel

5. ### KL7AJ AAC Fanatic!

Nov 4, 2008
2,182
415
I love my Simpson.

6. ### loosewire AAC Fanatic!

Apr 25, 2008
1,575
443
Can't the battery voltage in the probes of some old meters
burn transistors when you test them ?