Cosmopolitan build. Couple questions

[billstein]

Building a Cosmopolitan and have a couple of questions.

How do I know what the collector-base-emitter is on Q2 and Q3? Those transistors are round.

Does anybody have  suggestion for substituting the AC127?

Thanks guys,
Bill

[midwayfair]

How do I know what the collector-base-emitter is on Q2 and Q3? Those transistors are round.

Does anybody have  suggestion for substituting the AC127?

You'll have to look up the datasheet for the actual transistor you're using. You should use a socket anyway -- so you don't fry it.

Almost any germanium NPN with gain between 50 and 120 works fine in the Screwdriver. It can even have high leakage. The circuit's practically bulletproof. I like CV7112 [a little "rough"), MP38A ("A" range is important) (very smooth), and 2N130x (in between).

[billstein]

Thanks Jon. I guess what I was asking is when you see a parts layout, it's easy to tell how to place a transistor that has that same shape of being round with one side flattened, but when the transistor is round, is there a way to tell which one is the emitter? Just trying to find out if there is a key that I'm missing.

[midwayfair]

Thanks Jon. I guess what I was asking is when you see a parts layout, it's easy to tell how to place a transistor that has that same shape of being round with one side flattened, but when the transistor is round, is there a way to tell which one is the emitter? Just trying to find out if there is a key that I'm missing.

I don't like to give rules because the pinout might be different for any particular transistor. You really do need to look up the datasheet.

If you're just not sure on the layout, you'll have to trace the pads against the schematic.

Again, use a socket to be sure.

[alanp]

Sorry for the dredge 

Just ordered a load of MP38A, I'm going to have a lot left over from my project! (Hopefully I can find uses in the Hipster or the Brown Source or something.) It's a Russian transistor, the datasheets are in English, right?

[midwayfair]

Sorry for the dredge 

Just ordered a load of MP38A, I'm going to have a lot left over from my project! (Hopefully I can find uses in the Hipster or the Brown Source or something.) It's a Russian transistor, the datasheets are in English, right?

Well, you can find datasheets in English but the diagrams will be in English, or, interestingly in German. If you ordered from Gordeluxe, chances are you'll get the original datasheet in Russian. Which is cool if you speak Russian. Not so cool for those who don't!

Fortunately, you only need to recognize the first letter in the diagram.
K = collector
The one that looks like a lower case d with a tail is a B = base
The letter that looks like a 3 is an "Eh" = Emitter

With the pins facing you, the pinout is:
C      E
    B

i.e., same as most continental DO-18 silicon transistors and nearly all 3-pin germanium transistors.

By the way, I think there's a whole thread on Russian germanium transistors.