Germaniums with 4 leads: Why

[c a l a n d e]

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

 

[Dave Platt]

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.

www.nteinc.com 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.

http://www.nteinc.com/specs/100to199/NTE160.html

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[Michael Black]

Dave Platt (dplatt@radagast.org) writes:

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.

www.nteinc.com 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.

http://www.nteinc.com/specs/100to199/NTE160.html

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.

Michael

 

[Watson A.Name - "Watt Sun]

In article <f6oMb.6028$zj7.2852@newsread1.news.pas.earthlink.net>,
r86calande@earthlink.net mentioned...

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

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.


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[c a l a n d e]

c a l a n d e wrote:

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

Thanks for the prompt response.