I borrowed a multimeter...

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Tatosh
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Joined: Tue Nov 08, 2005 5:02 pm
Location: South

I borrowed a multimeter...

Post by Tatosh » Sat Dec 31, 2005 10:19 pm

I just got it and I want to be sure if its ok to use this. If it isn't then I will just return it and go buy one or something. I don't want to use this one if it isn't safe and besides it isn't mine... :wink:

anyway, it says TULMEX 16-30 it is quite msall, with a digital display. specs in the front say:

500V MAX
200 mA MAX
FUSED

is it ok to use this for taking readings in an amp? this would be for checking the tranies and for biasing my Superlead and Superbass.

My guess is that this wont be enough. Which is the best option?
1984 Gibson Explorer
home made Strat with fender and Warmoth parts and Duncan PUs.
1969 Marshall Superbass
1971 Marshall Superlead
Legendary Tones Time Machine Boost
THD Hotplate
Avatar cab 412 with G12 H30s.

Billy Batz
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Post by Billy Batz » Sun Jan 01, 2006 1:09 pm

Your pushing it with the 500v max. That said I have used my cheapy shitshack DMM to read voltages before in amps I knew where less then 500v. Those RS DMMs are rated for 500v as well and when the voltage approaches 500 like say 495, the readings get all 'funny'. If its going to be your main DMM get another. I use that one for reading resistors mostly. I got an Elenco off ebay for $11 and $10 shipping. The thing is $80 retail and it reads everything. Continuity, resistance, capacitance, diode, transistor, freq, signal gen etc...

Tatosh
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Posts: 115
Joined: Tue Nov 08, 2005 5:02 pm
Location: South

Post by Tatosh » Sun Jan 01, 2006 10:27 pm

I returned it today and bought one that goes up t 1000VDC. Used it today to great results... :D
1984 Gibson Explorer
home made Strat with fender and Warmoth parts and Duncan PUs.
1969 Marshall Superbass
1971 Marshall Superlead
Legendary Tones Time Machine Boost
THD Hotplate
Avatar cab 412 with G12 H30s.

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novosibir
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Post by novosibir » Sun Jan 01, 2006 10:45 pm

The best multimeter money can buy is the Fluke 87 - look at eBay, there you'd get it sometimes used for not much more than 100 US$

In mA mode the Fluke has an internal resistance from ONLY ONE OHM !!!
What makes very easy biasing amps exactly with the transformer shunt method.

Think about, that a half OT's primary has a DC resistance of about 15 ohms. That means, that by measuring with the shunt method through the meter runs 15 times more current, than through the measured half OT's primary - means 15/16.

So the equation for a EL34 fitted 100W amp is easy:

Measured current (in amps) : 15 * 8 * B+ : 25 (max. plate dissipation) = dissipation's value

Example:

.068A (68mA) : 15 * 8 * 460V : 25W = .6673 = 66.73%

Just my recommendation

Larry
The fault almost always is sitting in front of the amp :wink:

Larry's Website now with included Pix's Gallery

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