Connect with us

Germaniums with 4 leads: Why

Discussion in 'Electronic Components' started by c a l a n d e, Jan 12, 2004.

Scroll to continue with content
  1. I've been salvaging transistors from some old AM/FM/SW radios and have a
    number of Hitachi 2SA234 and 2SA235 types.

    My limited research has told me these are high frequency transistor used
    in the RF mixer sections. But what I don't know is what's the purpose of
    the forth lead and what the pin-out is.

    Your help would be appreciated
  2. Dave Platt

    Dave Platt Guest says that the 2SA234 crosses to an NTE160. The latter
    is a PNP germanium (!) mesa transistor, designed for mixer and
    oscillator applications up to 900 MHz. The fourth lead appears to be
    a connection to the metal case - presumably this lead would be
    grounded in most applications.
  3. And of course it's not unique to germanium transistors. I can think
    of various silicon transistors with a fourth lead connected to the case.
    (Mind you, at least some metal cased transistors have the collector
    connected to the case.) It's surely the intended application, RF
    and maybe some other crucial uses, that adds that fourth lead,
    rather than the semiconductor used in the device.

    Though, from memory it does seem that fourth leads were fairly common
    in cheap radio transistors thirty and so years ago. I have no
    idea if that's because they figured it was needed, until they
    realized otherwise, or if it simply disappeard as metal case transistors
    became less common. Obviously, many/most transistors in those
    cheap radios been plastic cased for two or three decades.

  4. Not sure about that particular transistor, but most all of the RF
    tranaistors of those years had a metal package, with the fourth lead
    connected to the metal package. So that lead is grounded, to shield
    the transistor from the rest of the circuit.

    @@[email protected]@[email protected]@@[email protected]@[email protected]@[email protected]@@[email protected]@[email protected]@[email protected]@,@@[email protected]@[email protected],@@[email protected]@[email protected]@[email protected]@
    ###Got a Question about ELECTRONICS? Check HERE First:###
    My email address is whitelisted. *All* email sent to it
    goes directly to the trash unless you add NOSPAM in the
    Subject: line with other stuff. alondra101 <at>
    Don't be ripped off by the big book dealers. Go to the URL
    that will give you a choice and save you money(up to half). You'll be glad you did!
    Just when you thought you had all this figured out, the gov't
    changed it:
    @@[email protected]@[email protected]@[email protected]@[email protected]@[email protected]@[email protected]@@[email protected]@[email protected]@@[email protected]@[email protected]@[email protected]@[email protected]@[email protected]@[email protected]@@
  5. Thanks for the prompt response.
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day