Bias Current Checker

[plexi50]

I built the bias current checker using Dougs diagram and directions. I am getting no measurments at all when plugging in the amp socket and then installing the tube

I used JB Weld to fill the socket cavity and it isnt going no where

I have checked all tube pins individually and everything is wired correctly including #8 cathode pin through meter and back to pin #8 cathode

Does cathode pin 8 of a EL34 have to be ungrounded for this to work? I would not  think so/////////

[sluckey]

Does cathode pin 8 of a EL34 have to be ungrounded for this to work?

no

[plexi50]

If i built this according to Dougs diagram then this should work right? I have had nothing but trouble from the mete im using floating around and unstable even checking resistors

Dam 3 meters in a month. I cant believe this Vellman meter could be bad. The socket wiring is perfect as per the diagram.........

[plexi50]

It works using a new meter. Dam how many of these things to i have to keep in stock
I simply need a good professional bench meter. I not going to buy any more of these DVM hand helds

The best one i had lasted a year and since then all i have been getting is crap

Well at least i know that it works

Im building a bias master to make life much easier

[sluckey]

If you're gonna be a professional, get a good meter. You won't regret it. Tradesmen are very often judged/measured by their tools. If that's a VELLEMAN DVM850BL, my lead set cost more than that meter. Just do it. Forgo one or two conversion projects and get a meter that will do you proud.

Did I mention Fluke?   ;)

[plexi50]

Yep it does pay to have the right tools and im sick and tired of buying a meter every other month. The fuses are not blowing in them either so im going to take your suggestion and Fluke it

[FYL]

I simply need a good professional bench meter. I not going to buy any more of these DVM hand helds

Get a Fluke - basic 8XXX models can be found second hand at more than decent prices. And their handhelds are really nice, too...

[PRNDL]

For the bias meter, how about getting a digital LED amp meter -- they're inexpensive ($15 on the bay). You could get one for amps and another for volts.

http://cgi.ebay.com/3-Digital-Red-LED-DC-0-2A-Amp-Panel-Meter_W0QQitemZ230236517007QQihZ013QQcategoryZ4678QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

I'm wondering what you did to burn out the DVM, or if it's because it's digital, and my trusty old cheap one is sturdier.

[plexi50]

I'll keep my eye out for a fluke at a good price. I dont know why all of a sudden i am having meter problems. I took the first velleman back because it was floating all over the place when testing resistors. The second one worked for about a week and then it started reading resistors out of the range it is switched to read within. My protek 122  was a cheapy but it worked great for a year or more and it was fully automatic in the readings other than having to switch it occasionally to m.a. or diode position. They no longer make the Protek 122. (Korea)

[rafe]

I have the one I made hooked permanently to a dc milliampere gauge
makes it easier for me. I got it for a couple bucks. [smiley=2vrolijk_08.gif] R

[PRNDL]

A used fluke 8012a may be a good candidate for those on a budget.

[bigugly]

well, in the second pic you posted it looks as though your red probe lead is inserted into the Volts/Ohms socket and it needs to be in the socket for Amps.

[sluckey]

well, in the second pic you posted it looks as though your red probe lead is inserted into the Volts/Ohms socket and it needs to be in the socket for Amps.

No, he's in the right input jack for ma (volt/ohm/ma). The 10Amp input is strictly for high current.

[PRNDL]

well, in the second pic you posted it looks as though your red probe lead is inserted into the Volts/Ohms socket and it needs to be in the socket for Amps.

No, he's in the right input jack for ma (volt/ohm/ma). The 10Amp input is strictly for high current.

The difficulty is that input has a 200 mA fuse. It's common for bad tubes to exceed 200 mA!

There are several possible solutions, but the easiest would be to use a 1% 1 ohm resistor and measure the voltage.

[tubesornothing]

I was thinking the same.  Rather than measure current directly through the meter, solder a 1ohm 1% resistor from pin 8 socket to pin 8 plug with leads on either side.  Then use the voltage setting to measure the current.

Since yours is already "welded" together, you can just strip the leads at the meter plugs and bridge a resistor.  Or Strip the leads at the plug/socket and solder on a 1R/1%. Then wrap in tape or heat shrink.

+1 on the fluke.  You'll never need another meter again.

[Nigel]

I built the bias current checker using Dougs diagram and directions. I am getting no measurments at all when plugging in the amp socket and then installing the tube

I used JB Weld to fill the socket cavity and it isnt going no where

I have checked all tube pins individually and everything is wired correctly including #8 cathode pin through meter and back to pin #8 cathode

Does cathode pin 8 of a EL34 have to be ungrounded for this to work? I would not  think so/////////

I set my bias using a signal generator and a scope.
I put a signal in that gives half voltage out on the output transistors.
I set the bias to zero to start with then lift it slowly until the crossover distortion goes.

[jhadhar65]

>...until the crossover distortion goes.

And that happens at exactly what idle current for you?

[Nigel]

>...until the crossover distortion goes.

And that happens at exactly what idle current for you?

It varies as the output MOSFETS arent matched.
The sum of the currents is around 100mA.

[jhadhar65]

Somehow I missed the word "transistors" in your previous post and was thinking tubes.  My follow up question would have been, "Do you supplement your scope with a meter".  I can tell from your reply, though, that you do this with your MOSFETs anyway.