Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => AmpTools/Tech Tips => Topic started by: CAMSHAFT on May 13, 2011, 11:50:03 am

Title: Current meter instead of multimeter?
Post by: CAMSHAFT on May 13, 2011, 11:50:03 am

Hello,
  I recently bought and built a Hoffman bias checker.
I am concerned because my multimeter manual says not to
Leave it in the circuit for more than 15 seconds!
I'm wondering if i can use a milliamp current meter
Instead, and if then i could keep it in the circuit indefinitely.
Can anyone offer me any good advice?

Title: Re: Current meter instead of multimeter?
Post by: RicharD on May 13, 2011, 06:49:27 pm

The Hoffman current checker has a 1 ohm resistor so you are actually reading voltage and not current with your meter.  Since we know that E=IR, and R=1, then E=I.  Much safer approach for the user, and the meter. 

Title: Re: Current meter instead of multimeter?
Post by: CAMSHAFT on May 13, 2011, 07:38:44 pm

Yes, I see what you're saying, but the version of the one i have does not have a resistor and
measures current. 

Title: Re: Current meter instead of multimeter?
Post by: sluckey on May 13, 2011, 08:46:52 pm

Quote

The Hoffman current checker has a 1 ohm resistor

I don't think so...   :think1:

Quote

I am concerned because my multimeter manual says not to
Leave it in the circuit for more than 15 seconds!

I've never seen that warning. What multimeter do you have?

Quote

I'm wondering if i can use a milliamp current meter
Instead, and if then i could keep it in the circuit indefinitely.

Absolutely.

Title: Re: Current meter instead of multimeter?
Post by: PRR on May 13, 2011, 09:46:37 pm

> not to leave it in the circuit for more than 15 seconds!

At HIGH current, the internal resistor may over-heat. The 20 Ampere range could be dissipating 4 Watts inside the plastic case, not good.

Tubes suck 0.05A, maybe 0.2A in extreme beast-amps. This is 0.04 Watts or less. The multimeter can carry that continuously forever.