SFT358/2SA246 have 4 legs...why???

[gigimarga]

Hello,

I've just grabbed a couple of NOS germanium PNP transistors from a store (big deal...30-40 transistors at 2-3$ )...but when i've came home i saw, between 2N404/SFT229/SFT242/2SB77 that i've already used in the past, some strange transistors with 4 legs: SFT358 and 2SA246...i've searched on the Internet but i didn't found anything to help me...anyone knows what are these transistors?

Thx a lot!

[theehman]

It's likely that the extra leg is attached to the case, if they're metal can transistors.  You can either clip off the extra or solder it to ground. 

[gigimarga]

Thx a lot!!
You're right - they are metal can transistors!

[foxfire]

the 4th leg is supposed to help with noise so it may be worth it to not just cut them? rylan

[spudulike]

Be careful - you need pinout details.

Because of the inherent noise in Ge pn junctions, transistors designed for RF use included an internal screen brought out to the 4th lead for grounding. The lead connected to the case may actually be the collector. If you check TO-3 power tranny cases the collector is the case (heat dissipation reasons) which is why you need to insulate them from the heatsink.

[gigimarga]

...if they are RF trannies...can i use it for Tonebenders/Fuzz Faces??

[Paul Perry (Frostwave)]

Being a RF transistor just means it is guaranteed to have gain up in the RF area. It won't stop it working in a fuzz, if the gain & leakage are OK.

[gigimarga]

Ok...thx a lot Paul...i have over 20 transistors of this type