Can I check my bias with this fluke

[Samhain]

Volts

It would get you in the ballpark to check them, but if you want increased accuracy you're going to need a multimeter that can measure millivolts specifically and not just volts.

You can't measure millivolts by measuring "volts".

 

[Samhain]

Right ? I was surprised too . Probably run to Home Depot for a 20$ one

You'll pay about $45 at home depot.

 

[glpg80]

You can't measure millivolts by measuring "volts".

0.004V is identical to 4mV

 

[Smash]

0.004V is identical to 4mV

Math

 

[glpg80]

Just checked your fluke T5-1000 manual. It has a 1V resolution. It's not precise enough to bias your amp. You need mV for that.

This is the real problem though - the meter doesn’t have the resolution set to Volts to capture millivolt changes. Some do - it’s all about their autoranging capabilities and resolution accuracy.

 

[Samhain]

Yeah that’s part of the reason I’m wanting to experiment with it . It sounds good but I’m curious to roll some nos el 34s and bias it a little hotter . I don’t know if current draw has anything to do with actual temperature? But compared to my old wizards and my Matamp. The fortin is “warm” after about an hour of playing at moderate to low volume . After about 30 mins on the Matamp you could start a fire

Current draw or Z of the tubes has EVERYTHING to do with if the tubes are going to work or meltdown/blow or whatever.
You're much better off with a new quad of Russian EL-34's.
Even if the NOS 34's bias right the difference in tone or whatever is negated.
You want matched power tubes to be sable & bias correctly for stable non-hassle operation.

 

[Samhain]

This is the real problem though - the meter doesn’t have the resolution set to Volts to capture millivolt changes. Some do - it’s all about their autoranging capabilities and resolution accuracy.

volt = 1.
millivolt = -.001 [ten to negative 3rd]

 

[Samhain]

Math

correct.

 

[glpg80]

volt = 1.
millivolt = -.001 [ten to negative 3rd]

1 volt is 1000 millivolts.

-0.001 millivolts is equivalent to -0.000001 volts. The negative sign indicates the flow of current and is meaningless here.

 

[Smash]

1 volt is 1000 millivolts.

-0.001 millivolts is equivalent to -0.000001 volts. The negative sign indicates the flow of current and is meaningless here.

Yeah. that's why i told the op to ignore the charge. It is irrelevant and often is from mixing up the probes, which doesn't really affect anything.

 

[scottosan]

You don't need a mA setting nor a bias probe. You could measure the resistance across output transformer primary (from each end to center point) and then measure voltage drop across each side of the primary. First, with the amp off, clip one probe to pin 3 of power tube then probe center point of primary to measure resistance. Should be between 10 and 20 ohms roughly. make that for each pair (or single) of power tubes.

Then with the amp on, clip one fluke probe to ground then with the other probe, measure plate voltage (power tube pin 3). Then measure output tranny primary center point voltage. Subtract value from plate voltage, it gives you voltage drop. If your wall voltage fluctuates too much, you could clip one probe to pin 3 and the other to center tap to measure voltage drop directly. Be careful with your hands in the running amp. Then with ohm's law (U=R*I or I=U/R), divide voltage drop with measured primary resistance, it gives you mA for that side of the output tranny, either a single tube or a pair of tubes. If it's a pair of tubes, divide by 2. Same value as measured with bias probe.

I did that no later than last week on my SLO and one of my 2203 that was giving me trouble. Put new tubes in and biased them that way. Worked fine, was quick, everything measure as it should and it sounds great. I used 35mA for EH EL34 (70mA for a pair of tubes) in the 2203 and 30mA for Sovtek 5881 wafer base (60mA for a pair of tubes) in the SLO.

That is not good advise for someone that doesn’t even know how to set the multimeter