Transistors hFE ~400?

[thermionix]

I want to try some 400-ish hFE transistors in my wah, but I don't have any.  I've got a bunch (2N3904s, 2N2222As, etc) with hFEs under 300.  I've got forty 2N5088s, a few 2N5089s, all hFEs over 500.

What's a good part number to look for, so that if I buy 20 or so I have a good chance of getting a few in the 400 to 450 range?

[Slowpoke101]

Have a look at the MPSA18 transistor. It may meet your needs.
Also they are used in some of the Crybaby Wahs.
They are just normal BJT devices and not darlington such as the MPSA13.

[thermionix]

I have looked at those, they seem to have typical hFEs quite a bit higher than 500.

I started off with a pair of BC109Bs, before I knew about hFE and just how variable transistors were.  IIRC the two I have are in the low 300s or maybe even 200s.  They sound nice, very glassy, but I would like a little more growl.

I tried 2N5089s in the mid-upper 500s, and that was too much, particularly for Q1.  So I have it in my mind that something in between would be right for me.  I bought the forty 5088s with the hope of finding some 400-450, but they are all very consistent in the mid-500s.  That's okay I needed resupply of those anyway.

I know I can tweak resistor values, but I'd like to try and get the sound I want with the stock values if possible.

[Slowpoke101]

Yes, the MPSA18s may be too high in gain for what you want.
I would suggest that you consider BC549B or BC550B series transistors.
The suffix generally indicates approximate gain range.

http://www.mouser.com/ds/2/149/BC550-888526.pdf

[Plexi]

I agree with BC550B.
Almost every I've used, was in the ~400 hfe range.

[thermionix]

Thanks, I'll add those to the list of possibilities.  Tayda lists a BC550 for $.03 a pop, but they don't specify a suffix.  I could order 200 of those and it will do me no good if they are all As.

Mouser has BC550B for $.15 each, but I'd probably have to buy quite a few to get the hFE range I'm looking for, which is right in the top B or bottom C range.

I'm eyeballing some Telefunken BC108Cs at Small Bear, probably better chance of hitting the desired gain, but too expensive to get a bunch of them.  (Though I am a sucker for anything made by Telefunken, Mullard, Amperex, or RCA).  Maybe I will buy 4 or 5 and hope for at least one ideal Q1 candidate.  Q2 is far less critical for me, but it would be nice get both in that range.

[thermionix]

Thanks Plexi, I was typing when you posted.  What brand or supplier are you getting those from?

[R.G.]

Um... I know I'm a pest about this, but why do they need to be 400-500?

[thermionix]

Um... I know I'm a pest about this, but why do they need to be 400-500?

They don't need to be, in order to work.  I'm just trying to zero in on a particular sound, a certain amount of "snarl" (I mistakenly said "growl" earlier, totally different thing).  I think it occurs in a pretty specific Q1 hFE range, but I don't really know yet, just experimenting.  Going through transistors I have on hand, seems to ba a gap in the range I'm looking for.

However, I've now rendered this thread essentially moot, because I just went full mojo nuts-o and ordered a 5-pack of these:

https://www.ebay.com/itm/222043812064

Same as original Thomas Organ "5117" part.  Gain range looks nice (fingers crossed).  Mouser has new manufacture 2N2925s for less, but they don't look as cool.

[R.G.]

OK. Good answer. Carry on.

[amptramp]

There was a circuit that showed up once in these pages where the resistor and base junction of the input stage were in parallel with a resistor and diode connected so some of the input current would divert into the diode.  The diode junction was in the same direction as the B-E junction of the input transistor and the other end of the diode was connected to the emitter of the input transistor.  By juggling resistance values, you could use a very high-gain transistor and tune it down to a lower gain to meet your requirements.

[mac]

BC549C
2SC2240

mac

[Plexi]

Thanks Plexi, I was typing when you posted.  What brand or supplier are you getting those from?

Fairchild!

Take a look closer to the Tayda's description:
Manufacturer: FAIRCHILD
Manufacturer Part No: BC550B
Package / Case: TO-92
RoHS: Yes
Datasheet: Click Here

They're 'B' rated 

Another one I would recommend is 2N4401, they're almost that range too

[thermionix]

Ah, you're right!  They should just say BC550B in the main list then.  I'll still look into those in the future to cover that hFE gap in my selection.

But, as we all know, Mojo is just a bit too big to fit into a TO-92 package.  So I had to go with the TO-98 style instead.

I'll update in a week or so with a "Best wah ever!" post when I get the 2N2925s installed.

[bool]

You should look after "B" suffix not "C"

BC549B, BC550B

With more parameter variance and a bit noisier BC548B.

[Guurf2]

i think the BC183C has around 400 in hfe, also i think the older style BC109 (mine don't have a suffix).
the BC183C is a bit noisy though.

[duck_arse]

Ivan at diy-tubes.com measured-for-gain some transistors for me recently. he might fix you up with some BC series, or maybe some big-muff types.

[no affiliation.]

[thermionix]

These five NOS 2N2925s showed up.  The hFE gods did not smile upon me today.  They all tested on the low side of, or below, the supposed range.  Still, I put the best two (hFEs about 260) in my wah to try them out.  They work, no noise problems, don't sound bad per se, but don't get me anywhere closer to my goal.  Very clean.  I guess I'll order 10 or 20 of the new ones from Mouser, and hopefully get at least one high gainer for Q1.  Or maybe just get the BC550Bs from Tayda.  I'll leave the NOS type in Q2, I think 260 is fine there.  For now, BC109B is going back in for Q1.

Oh well, wasted 9 bucks, not my worst mistake in life.

[Plexi]

That's why you never have to believe in mojo haha :-D

[thermionix]

Yep, got caught worshipping false idols, and paid the price.

On the upside, the experience seems to have confirmed that it is a specific Q1 hFE range I'm looking for, rather than some other characteristic.  These NOS transistors don't sound any different than some similar 2N3904s I tried months ago.  The BC109B I put back in tests about 315, and is definitely closer to the sound I'm after.