Four terminal Ge transistors

[lopsided]

Hi,

I have come across a couple of germanium transistors with a pair of GF506 among them.
These transistors have four terminals. Any idea what they are and what they could be good for?
The fourth terminal is called "S" here http://katalogy.ic.cz/GF506.html , but I do no get what that should stand for.

J.

[CynicalMan]

Probably substrate.

[ubersam]

The "S" could mean shield. I have some like that with four lead and the fourth lead is connected to the can.

[gritz]

^This rings a bell^

The fourth lead is a shield and if my addled memory serves me right it's to reduce the Miller capacitance coupling between base and collector (or something!) The shield lead is (I think) connected electrically to the can and should be grounded.

However... I believe that some (Mullard?) trannies suffered internal migration of the can plating which could short the die to ground. IIRC a hack that sometimes worked was to cut the shield lead. Remember that these transistors are radio frequency (VHF, or thereabouts) items , so the shielding isn't a big deal at audio frequencies, but they might not have a great deal of gain.

Even so, it would be a shame not to test them and maybe get them to bend some sound.

[LucifersTrip]

...and what they could be good for?

anything....you just chop off the extra leg and use it as any other normal transistor. I've done that many times...

[lopsided]

The "S" could mean shield. I have some like that with four lead and the fourth lead is connected to the can.

This is it, DMM confirmed this. Thank you all.
Unfortunately this particular pair seems  to be excessively leaky. I measure about 7 V across the 2,4V resistor in the geofex test. Have breadboarded the tonebender input stage just to try them and they just fart very badly no matter how the C resistor is adjusted.
Luckily some other types I got passed this test, so I will try them out in some circuits.