Cosmo - transistor orientation

[Bret608]

Hi everyone,

I'm planning to test my Cosmo build tonight, and I want to ask about transitor orientation since I went "off road" on some of the tranny choices.

For Q2, I'm using one of the high-gain BC108s from Smallbear per JakeFuzz's suggestion. Will this be oriented as per the build doc, or the reverse?

For Q3, I'm using a cool 2n1304 that JakeFuzz kindly shared with me. Will that one go with the build doc?

Thanks in advance guys!

Cheers,

Bret

[jtn191]

the BC108 should be fine, I couldn't find much info on the datasheet about the 2n1304. my guess is that'll it'll work too

[Bret608]

Thanks man! The BC108 was fine alright...I couldn't get anything too conclusive from the 2n1304 datasheet either, so I just oriented it as per the build doc and it fired up with no problems. Build report in a few!

[Bret608]

Hi again,

Sorry to gravedig my own thread here! Due to a recent mental breakthough on understanding transistor pinout, and how that plays out with the different transistor packages, I'm going back and looking at prior builds to make sure I've got things right. Could someone let me know if I have Q2 oriented properly here? It's a BC108, an NOS from Smallbear. I looked at other build reports, but I've seen it both ways. If you're looking at the component side from above, should the emitter tab be facing "northwest", or "southeast"?

Thanks!



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[midwayfair]

There's a much better way to tell. The little wing is the emitter. According to the schematic, that should be connected to ground. You can use your multimeter to check -- just probe any ground point and the pin on the transistor closest to the wing.

The reason it's a little confusing is because the etch picture used a TO-92 package instead of the metal can. The TO-92 looks "backwards" from the metal can.

[Bret608]

Thanks Jon! I am glad it was you who answered. Quick follow-up question or two...should I be getting 0 volts on that pin? And would this methodology apply to Q3 as well?

You're right, understand the TO92 image's backwardness relative to the metal can is the mental "breakthrough" I mentioned!    I suspect I have both of these backwards. The pedal does work, but not at its best if I'm right about this.

[Bret608]

Just a quick update...check the transistor datasheets for the ones I used against the schem and layout diagram, and sure enough they were as backwards as the day is long! Flipped them the right way and it sounded like I took a blanket off the pedal or something, it's just amazing. This has been educational--there are more circuits out there than I thought that can kind of work with the trannies oriented improperly. If you're like me and haven't always heard the original pedal enough to know something is wrong, you can go some time before correcting it. I realize now that both this and my Pepper Spray sounded kind of weak and mis-biased. I'm glad I know what to do going forward, though!