Transistors in parallel + simulating leakage

[polifemo]

Hi,

I'm new to Fuzz design but I've been doing a lot of reading lately and a couple of days ago I came across the idea of connecting Silicon transistors in parallel in order to reduce gain (often needed as silicon trannies are way hotter than the germanium ones).

I've bought a PEAK atlas DCA55 component analyzer that takes readings of HFE (+ many other things) but when I solder two transistors together I still get half the same HFE measurement instead of half the gain, which was what I expected...

I've also heard about simulating the leakage - from collector to base - in GE trannies by connecting a large resistor from collector to base on a silicon transistor but when doing so I don't get an reading of leakage as it remains at "Zero".

Something DOES happen though!
Gain now have dropped from about 330 (BC547B transistor) to 7 !?...
And what seems even stranger, collector and emitter have now "switched places" according to my component analyzer !?...

Will these things: "transistor in parallel/half the gain" and "leakage resistor" work differently IN a circuit?

Someone please explain

[DrNomis]

Hi,

I'm new to Fuzz design but I've been doing a lot of reading lately and a couple of days ago I came across the idea of connecting Silicon transistors in parallel in order to reduce gain (often needed as silicon trannies are way hotter than the germanium ones).

I've bought a PEAK atlas DCA55 component analyzer that takes readings of HFE (+ many other things) but when I solder two transistors together I still get half the same HFE measurement instead of half the gain, which was what I expected...

I've also heard about simulating the leakage - from collector to base - in GE trannies by connecting a large resistor from collector to base on a silicon transistor but when doing so I don't get an reading of leakage as it remains at "Zero".

Something DOES happen though!
Gain now have dropped from about 330 (BC547B transistor) to 7 !?...
And what seems even stranger, collector and emitter have now "switched places" according to my component analyzer !?...

Will these things: "transistor in parallel/half the gain" and "leakage resistor" work differently IN a circuit?
Someone please explain

When you connect a large value resistor from a Silicon Transistor's Collector to it's Base, the resistor biases the transistor "on" by diverting some of the current from it's Collector to it's base...

Silicon Transistors typically exhibit leakage-currents in the order of Nano-Amps, one Nano is one one-thousandth of a Micro-Amp, Germanium Transistors typically exhibit leakage-currents in the order of Micro-Amps, so the Leakage Current is about a thousand times greater than for Silicon Transistors....

[polifemo]

In my initial post the word "Half" was misplaced due to a cut n´paste procedure....


"I've bought a PEAK atlas DCA55 component analyzer that takes readings of HFE (+ many other things) but when I solder two transistors together I still get ( half) the same HFE measurement instead of half the gain, which was what I expected..."

I meant that I get THE SAME READING!

My component analyzer do not display any leakage at all when soldering a 1 meg transistor from collector to base.
Maybe I should try a really small one?

I´ll be able to test IN a circuit when some new compnents have arrived

[DrNomis]

In my initial post the word "Half" was misplaced due to a cut n´paste procedure....


"I've bought a PEAK atlas DCA55 component analyzer that takes readings of HFE (+ many other things) but when I solder two transistors together I still get ( half) the same HFE measurement instead of half the gain, which was what I expected..."

I meant that I get THE SAME READING!

My component analyzer do not display any leakage at all when soldering a 1 meg transistor from collector to base.
Maybe I should try a really small one?

I´ll be able to test IN a circuit when some new compnents have arrived

HFE is basically the same as a Transistor's gain, what you are actually measuring is the Transistor's "Current-Gain" (assuming it's a Bi-Polar Transistor), that is, how much larger the Collector-Current is compared to the current flowing into the Base of the transistor, say for example the HFE of the transistor is 200, if we apply a current of 1 micro-amp to the transistor's base, we would have 200 micro-amps Collector-Current, another name for a Transistor's Current-Gain that's commonly used is "Beta"....

The Collector-Current of a Bi-Polar Transistor is calculated using the following Mathematical Formula:

Note:

Ic = Collector Current.

Ib = Base Current.

B = Beta, or HFE (Current Gain).


Ic = Ib X B


Try changing the 1M resistor to a lower value resistor, say 100k, or maybe 220k....