Transistor Testing Ports In Multimeters: Junk?

[chris.knudson]

Gah! In that case, the "better" more expensive tester would be the one for builders to trust I'd think, but again - why?

This actually reminds me of a lesson I learned from an electrician I hired. I hired a guy to troubleshoot an electrical issue in my house. I expected him to show up with testers and probes and meters, etc. He shows up with a lightbulb connected to two probes. I was like, WTF dude, I'm paying you good money to diagnose a problem in my house, and you show up with a light bulb. He says to me, "I can diagnose any electrical issue you have in this house with this simple tool." He found the problem in 5 minutes and spent the next 55 minutes (of the hour I paid him for) showing me how to use a light bulb and two wires to diagnose any electric issue you'll ever encounter in household wiring -- best money I ever spent (on an electrician)!

 

[Ginsly]

This actually reminds me of a lesson I learned from an electrician I hired. I hired a guy to troubleshoot an electrical issue in my house. I expected him to show up with testers and probes and meters, etc. He shows up with a lightbulb connected to two probes. I was like, WTF dude, I'm paying you good money to diagnose a problem in my house, and you show up with a light bulb. He says to me, "I can diagnose any electrical issue you have in this house with this simple tool." He found the problem in 5 minutes and spent the next 55 minutes (of the hour I paid him for) showing me how to use a light bulb and two wires to diagnose any electric issue you'll ever encounter in household wiring -- best money I ever spent!

There are absolutely situations like this where more complicated/fancier/more expensive don't necessarily mean "better", but with testers (esp for Ge) and multi meters it seems like there could be some truth to it...? That being said, I love my TC1s! I'm just confused by the discrepancy in measuring a simple resistor between the TC1 and my multi meter... I figure that's one reading that would be pretty rock solid across the board.

 

[chris.knudson]

There are absolutely situations like this where more complicated/fancier/more expensive don't necessarily mean "better", but with testers (esp for Ge) and multi meters it seems like there could be some truth to it...? That being said, I love my TC1s! I'm just confused by the discrepancy in measuring a simple resistor between the TC1 and my multi meter... I figure that's one reading that would be pretty rock solid across the board.

Like I said in my earlier post -- every tester I bought was for a specific application and they all worked perfectly for what I bought them for. Your DMM wasn't designed to test components -- it's designed to test voltages, resistance, continuity, etc... The TC1 is specifically designed to test components -- so trust it for that.

 

[Ginsly]

Like I said in my earlier post -- every tester I bought was for a specific application and they all worked perfectly for what I bought them for. Your DMM wasn't designed to test components -- it's designed to test voltages, resistance, continuity, etc... The TC1 is specifically designed to test components -- so trust it for that.

Right - but the DCA75 was designed for components too, and it's giving @jwin615 differently results than his TC1... and a 3rd special component tester is different than those!

 

[chris.knudson]

Right - but the DCA75 was designed for components too, and it's giving @jwin615 differently results than his TC1... and a 3rd special component tester is different than those!

This is a case of you get what you pay for. If you are matching FETs or doing something that requires a level of precision, the DCA75 is a superior product.

EDIT: If you're just looking for open neutrals and shorts, a light bulb with two probes is probably a better choice.

 

[Ginsly]

This is a case of you get what you pay for. If you are matching FETs or doing something that requires a level of precision, the DCA75 is a superior product.

I'm not at the point of needing to do that yet, but I'm keeping this in mind for sure. It seems like the DCA75 (and adapter??) might need to go on a wish list...

 

[chris.knudson]

I'm not at the point of needing to do that yet, but I'm keeping this in mind for sure. It seems like the DCA75 (and adapter??) might need to go on a wish list...

It's already on my wish list

EDIT: That and a light bulb with two connected probes

 

[darwin999]

I'm starting to understand that, and the question I have is - which one is most relevant to pedal circuits? How would one pick a set of results if they had to (which they often do if they're selling them, I'd imagine).

Exactly the right question, and unfortunately it's not a simple answer - it likely differs for each circuit.
You need to measure under the conditions appropriate for the circuit under study, and then compare to what the testers are using to say which is closest (i.e., "best"). Odds are that neither instrument is going to be EXACTLY right for a given circuit when used in their hFE measurement.

For it's automatic hFE measurement, the DCA75 uses Ic = 5mA, which may be on the high side for many stompboxes (e.g., assuming a 9V supply + 1 to a few kOhm in series w/ the transistor, that implies a few hundred µA for Ic). HOWEVER, one major advantage of the DCA75 is that you can do a more detailed I-V trace of the transistor, and then evaluate hFE at the right value for Ic that corresponds to your circuit.

I just don't know what Ic current the TC1 or TC2 uses for its hFE evaluation - does anyone here know? Regardless, the TC1 only gives you one measurement at its chosen/fixed Ic value, there's no option for tracing or varying Ic.

Of course, another approach is to use the TC1 and/or DCA75 to get you close to the right hFE, and then let your ears take it from there...

 

[Ginsly]

I just don't know what Ic current the TC1 or TC2 uses for its hFE evaluation - does anyone here know?

Whenever you test, it says "Vbat = 3.83v" or however charged the battery is. Usually between 3 and 4v.

There seems to be some debate about how accurate TC1 hfe and leakage readings are, generally, for Ge transistors. Some say it matches up to the RG Keen method reliably, others say it's not even close.

It's good to know that there's not really one perfect answer. It seems like the RG Keen method is pretty reliable, but it seems like you really have to trust your multi meter when determining voltage across that 2.2m resistor. Plus, it's a little tricky to get that 2.472k resistor exactly right. The problem is, when choosing resistor combos for the test, I first have to test THOSE - and the TC1 and my multi meter gave me different DC voltage answers!

I tried the Keen test with a simple silicon transistor, which the TC1 is typically very reliable for. The results were VERY different between the TC1 and Keen method. I'm not sure if my resistors were too far off spec or if my multimeter is badly calibrated...