biasing help - strange reading on multimeter

[afterburner]

Hi everyone,

Need some help here... first time biasing my new Tweaker 40 amp.

Bought this multimeter and using it in the 200mV setting.
http://www.amazon.com/Equus-3300-Hands-free-Digital-Multimeter/dp/B001O1X65A/ref=sr_1_4?

Problem is, I get a reading of 06.5 instead of anything like the 65mV I'm trying to set it too.

Any ideas on what I'm doing wrong?

Thanks in advance!

 

[cap47]

Check your meter setting.

 

[Blue Strat]

Do the Tweaker instructions indicate you should read 65mV? The reason I ask is that it's possible to use a 10 ohm, rather than a 1 ohm, resistor for current sensing in which case you would read 6.5 versus 65.

What happens when you tweak the bias pot?

 

[oldhousescott]

According to a post by Bruce on that other board, it should be set for 65mVDC between test points 1 and 2, for 6L6s, 5881s, and EL34s.

Make sure the battery in your DMM is good. Try the 2VDC scale, it might give you 3 decimal places of accuracy, enough to measure .065 VDC.

 

[afterburner]

The instructions say 65mV.

The initial reading with the stock tubes were 07.3 or so. I got the amp used so I don't know what (if any) biasing was done. The bias pot is really sensitive to small adjustments, but I didn't try to see what the min/max I could get it to be was.

 

[afterburner]

According to a post by Bruce on that other board, it should be set for 65mVDC between test points 1 and 2, for 6L6s, 5881s, and EL34s.

Make sure the battery in your DMM is good. Try the 2VDC scale, it might give you 3 decimal places of accuracy, enough to measure .065 VDC.

Would the 200 mV setting be wrong? I will try the 2VDC later.

 

[Blue Strat]

Would the 200 mV setting be wrong? I will try the 2VDC later.

It SHOULD be correct but in a case like this you try different things just to be sure.

 

[afterburner]

It is labeled 10 MegOhm input impedance on the DC V settings part. Does that have anything to do with it?

Going to pull the chassis and try to take the reading again now...

 

[Blue Strat]

That's the input impedance of the meter which is more than adequate.

 

[VacuumVoodoo]

Low battery in the DMM?

 

[Blue Strat]

Low battery in the DMM?

This is ALWAYS worth checking when readings look flaky.

 

[afterburner]

Didn't check the battery yet...

BUT I did finally get it working. I turned the bias adjustment knob all the way down and gradually turned it up. It started showing readings in the proper range... and I got it to 65mV.

Will have to check the battery in the DMM.

Thanks everyone!

 

[Blue Strat]

Didn't check the battery yet...

BUT I did finally get it working. I turned the bias adjustment knob all the way down and gradually turned it up. It started showing readings in the proper range... and I got it to 65mV.

Will have to check the battery in the DMM.

Thanks everyone!

Congrats! Try another battery just in case though. It would really suck if you were really running them at 650mV.