2n3904 vs bc109?

MrCoolGuy

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If a fuzz pedal uses 2n3904 transistors... (a 2-transistor fuzz...) could you use bc109's instead? If not, why? They are both NPN... what am I missing?
 

loopfinding

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You can practically use any Si transistors you like for any fuzz, it’s just the biasing points and gain are going to be a little different. So you either have to tweak your resistor/coupling cap values, or maybe in some cases you want more or less of saturation/cutoff weird stuff.
 

MrCoolGuy

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You can practically use any Si transistors you like for any fuzz, it’s just the biasing points and gain are going to be a little different. So you either have to tweak your resistor/coupling cap values, or maybe in some cases you want more or less of saturation/cutoff weird stuff.
Yeah, i kinda understand that... and im willing to change values as necessary...
But I swapped in some bc109's in this circuit (instead of 2n3904's which worked fine) just to hear the difference... but i get nothing.
Screenshot_20211126-215412_Acrobat for Samsung.jpg
 

kbold

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BC109 pinouts are C-B-E
2N3904 pinouts are E-B-C

In other words you may have put it in backwards ... remove, turn around and resolder.
 

Wound_Up

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I replaced the 2n2222a's in my fuzz with BC109C's with no issue. Just make sure you have the pinout correct as long as they're both NPN.
 

kbold

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Tab is pin#1=Emitter. pin#2 is Base, pin#3 = collector common to case.
https://my.centralsemi.com/datasheets/BC107.PDF
What you say is correct, so I should perhaps rephrase or explain.

I am in effect referring to the plastic TO-92 packages. I use those as my point of reference: flat face forward, pins facing down.
2N3904 = E B C TO-92A package (labelled as pins 1 2 3)
BC549 = C B E TO-92F package (labelled as pins 1 2 3) BC549 is the plastic cased (non mil-spec) equivalent of the BC109.
Some TO-92 transistors have a rear offset to the middle leg, making their footprint the same as metal can packages (direct drop in replacement).
So you can rephrase the BC109 as:
BC109 = C B E Emitter at Tab TO-18 package (Labelled as pins 3 2 1)

(From Wikipedia)

TO-18
(C-B-E)


Emitter is closest to tab

I omitted the use of numbers to avoid adding confusion (which it seems to have done for you).

I stand behind my earlier post.
 

cherryburst1

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What you say is correct, so I should perhaps rephrase or explain.

I am in effect referring to the plastic TO-92 packages. I use those as my point of reference: flat face forward, pins facing down.
2N3904 = E B C TO-92A package (labelled as pins 1 2 3)
BC549 = C B E TO-92F package (labelled as pins 1 2 3) BC549 is the plastic cased (non mil-spec) equivalent of the BC109.
Some TO-92 transistors have a rear offset to the middle leg, making their footprint the same as metal can packages (direct drop in replacement).
So you can rephrase the BC109 as:
BC109 = C B E Emitter at Tab TO-18 package (Labelled as pins 3 2 1)

(From Wikipedia)
TO-18
(C-B-E)


Emitter is closest to tab

I omitted the use of numbers to avoid adding confusion (which it seems to have done for you).

I stand behind my earlier post.
Well, sorry but I'm not the one confused. The OP said he had BC109's, not BC549's. BC109's are not BC549's.
The BC109 is still available and it's original case, the TO-18. You are cross referencing different components with different pinouts. The BC549 was introduced later than the BC109 and has half of the current capabilities than the BC109, hence the TO-92 package..
THe OP stated he was using BC109's so we must assume he knows which transistor he has.
Therefore, the datasheet stands as reference. Tab (pin 1 Emitter, pin2 Base, pin3 [case] Collector.)
So unless the OP stated the wrong transistor number, I stand by my earlier recommendations...
 

MrCoolGuy

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They are NewJersey Semi. BC109's. TO-18. And from what youre all saying, I put them in correctly. I'm not sure whats going on. The pedal worked fine with the 2N3904's...
 
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cherryburst1

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Transistor checker? You might have a dead or leaky one...Cold solder joints should also be checked.
If no scope and generator, look at the voltages on the devices to see if E>B, E>C and B>C are correct. Low voltages, no voltage drop across collector resistors or wrong bias voltages E>B will help tell the tale....
 




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