HFE Testing Issue

[rocket88]

I recently purchased from smallbear a bunch of silicon transistors for some products. I decided I should probably start to test the HFE of my transistors before installing them, but I've found that what smallbear says they should be my tester tells me something different. For instance these  are supposed to average 210HFe, but when I plug them into the tester of my multimeter I get readings like 354HFE. I'm seeming to only have a real issue with older vintage silicon transistors, while newer ones seem to fall spot on like 2n2222a's from tayda I'm consistently getting around 200HFE. Should I build the germanium tester here, even though I'm not sure it will work for silicon, or just ignore the readings I'm getting and just assume they fall within range when building. I'm just worried that it will cause biasing issues if the HFE is higher or lower then what it would be expected, which will be a huge problem after the pedal is built.

[Silver Blues]

Well all you have to do is socket your trannies, and if you have a problem you can just swap it for another one.

[induction]

RG's transistor tester works with silicon as well as with germanium. The only difference is that silicon transistors have nearly zero leakage, so you can safely skip that part of the test. I doubt that it will give much different readings than your DMM, but I might be wrong.

Whether it makes a big difference in the biasing will depend on the circuit, but you can always socket them so you can swap them out. Or you can breadboard before you build, so you know it will bias correctly.

[rocket88]

I usually socket them anyways so that I don't have to worry about heating them too much, and I can easily replace them if need be. Any idea why i would be having such different readings? I've heard that sometimes vintage silicon transistors can give odd results, but not sure if its a problem with the tester on my multimeter. Also, when it comes to the transistors in schematics/layouts they never list the HFE, how does the HFE affect a circuit? Is it really much of a concern?

[Vince]

Buy one of these. Mark recommended it to me and it's invaluable now. So easy it's worth every penny

http://www.peakelec.co.uk/acatalog/jz_dca55.html

Also, I've found it really depends on the circuit. All the Death By Audio layouts are a pain in the arse when it comes to hfe's but I've found that the majority of layouts work well with the recommended transistors regardless of hfe.... excluding germaniums of course as they're more temperamental.

[Silver Blues]

rocket88 wrote

Also, when it comes to the transistors in schematics/layouts they never list the HFE, how does the HFE affect a circuit? Is it really much of a concern?

I read somewhere that a "good circuit designer" doesn't design his circuit around a transistor of a particular gain level. IME In a way this is true, because you'll find that most circuits work just fine with a wide variety of HFE numbers; the sound may be slightly modified, or the drive characteristic might be different, but it won't compromise the functioning of the circuit. Unless of course you're using germaniums (as Vince mentioned) but that's an issue more with temperamental bias (which will mess up your circuit's function) than gain.

[rocket88]

Thanks guys. I guess I'm going to break down and get a peak, its just they are so expensive, but I have some people that want me to build stuff for them so I guess it's really worth it. Am i right though that the Hfe for the most part really only affects the biasing or does it really have an effect on the sound? I know not all circuits are the same, but I just mean in general.

[Silver Blues]

rocket88 wrote

 Am i right though that the Hfe for the most part really only affects the biasing or does it really have an effect on the sound? I know not all circuits are the same, but I just mean in general.

I'd say if it has an effect it'll be on the sound, I haven't yet come across a circuit whose bias was messed up by using a 'high' or 'low' gain transistor of the same part number. There are of course some circuits, like my personal favorite the Muff, where the gain of the transistor doesn't play a really large part in the sound of the circuit (type does, though). I'll surely defer to a more experienced builder if I'm wrong but this is my experience if it helps you out.

[stringfellow_Hawke]

I stumbled across this thread about the DCA55 on DIYStompboxes recently and I think there are some pretty interesting insights. Definitely worth checking out. I also think it's worth noting that often on small bear you'll see an average HFE and sometimes you'll also get a high and low HFE. If you're only seeing the average in the description it's a safe bet that you're going to get transistors that are all over the map within the tolerance. I notice that when I'm checking data sheets the range listed is sometimes as much as +/- 200Hfe from the nominal, so it's likely perfectly normal to see the variances you're describing.

http://www.diystompboxes.com/smfforum/index.php?topic=91115.0

[Vince]

Personally, I've never experienced any of the issues they speak of. I use mine 99% of the time to measure germaniums for Rangemasters and Tonebenders etc. Of course it is just to get a rough idea of the hfe's so they can be placed in the recommended positions but ear plays a large part in it too. I built a ger fuzz face with AC128's q1=80 and q2=120... didn't like it at all then put 2 Russian IT308B's at 82 hfe and they sound fantastic, much lower hfe than recommended but they sound higher gain??... So the Peak should just be guide but ears should play the biggest part...

[rocket88]

Very interesting Vince. I've heard things like that before, which is why I'm still confused as to what the gain, Hfe, really does in a circuit. If you know what I mean?

[Vince]

There is some interesting info found in these videos. In one he speaks of the lower hfe sounding higher gain due to frequency ranges etc..

http://www.youtube.com/results?search_query=germanium+transistor+guide&oq=germanium+transistor+guide&gs_l=youtube.3...542.6615.0.6798.26.26.0.0.0.0.207.2522.20j5j1.26.0...0.0...1ac.1.11.youtube.8eNaLt2JePU

[rocket88]

Cool Vince. I've been watching his stuff for awhile, but didn't get to those yet. Some really interesting stuff, and really makes you think about it.