Low gain Si Tranny? I think so...

[Brossman]

Hey guys,

I was rummaging through a box of electronic components in the basement where I work (appeared to have been untouched for ~20-30yrs, based on the dust), and I managed to find some very interesting stuff...

I found a box of trannies, so I started looking up datasheets.  I forgot to write them down and/or save the dataheets, but I can always go back and check.  I was surprised that one of these had an Hfe rating of min. 40 - max. 120...  I didnt even think Si-trannies were available this low. Is it possible to use these little pipsqueaks in something that is low gain (normally Ge-tranny) circuit?  Maybe say...FuzzFace?

Thoughts?

[newfish]

Absolutely!

If you have a DMM with Hfe readings, sort your batch out into low / high order, then 'audition' the devices on a breadboard / socketed board.

If you haven't got access to a DMM, you could do a lot worse than simply swapping devices in and out of your circuit (sockets are a god-send here...)

I currently have a Fuzz Face clone with NPN Si devices of 40 (Q1), and 87 (Q2) - and it sounds great - really warm and 'bloomy'.

Good luck!

[Johan]

look at MPSA 42/92 for real low Hfe.
J

[~arph]

I like the 2N3440 thats 40 -160

[trjones1]

Datasheet for the PN2369A show it to be in the 40-120 range, though I've never measured one below 110.  Tried some in a fuzz face, they sounded ok, but then I'm not a huge fan of the fuzz face at this point.

[LucifersTrip]

loads of the vintage 60's transistors I own have hfe < 20 !

The 2N2222A metal cans that are sold now have hfe ~ 60
http://www.taydaelectronics.com/servlet/the-43/2N2222%2C-Transistor%2C-transistors%2C-npn%2C/Detail

Though, a couple of my modern favorites that don't have high gains are the 2n5550's and the 2SC1815's with gains of around ~ 100-150
They've worked well in some vintage silicon fuzzes.

[Gus]

You can also use med power transistors like a TIP29, TIP30 etc.

[Brossman]

Hmm, so on the topic of the FF, would I have to use a - gnd version to use NPNs, or can I rewire the circuit to run as per the old +gnd?  or...does that absolutely require PNPs?

[newfish]

If you have NPN devices, you'd be better using negative (conventional) ground.

You'll need to swap the +9v / Ground wires from the battery / DC jack, and also reverse the polarity of the 22uF cap (on the 'gain' pot) so the '-' terminal goes to ground.

That should be it!

[mac]

look at MPSA 42/92 for real low Hfe.

Nice transistors, also can be found as KSP 42/92

mac

[Gus]

Look at transistor data sheets and note Hfe vs Ic (collector current) graphs

Hfe can vary a bit with current AND the transistor tester used.

IMO the best way to use one is to build a tester that operates the transistor at the Ic etc of the circuit you want to use it in

Search for transistor tester.

[mac]

Look at transistor data sheets and note Hfe vs Ic (collector current) graphs

Hfe can vary a bit with current AND the transistor tester used.

IMO the best way to use one is to build a tester that operates the transistor at the Ic etc of the circuit you want to use it in

Search for transistor tester.

You can also use RG test to get hfe at different ic's. Assume leakage is zero.
http://www.diystompboxes.com/smfforum/index.php?topic=45481.0

mac