Mpsa13 booster questions

[Kipper4]

I just bought a bucket load of MPSA13s
Is there any useful projects to build with them?
What about a booster?
Could you make a booster with it but limit the gain?
If so how?
Thanks
Rich

[nocentelli]

[Kipper4]

Hey Leo
So the idea there is limit the signal on the input?
I guess its not a limit the transistor gain type circuit right?
thanks

[nocentelli]

Or something like this? Might try it myself this afternoon. I suspect it it will get quite gritty as the 1k gain pot is turned up, but you could dial it up to where it starts to clip then back off a hair (or have it as a trimmer to set the "headroom") and replace the 220k with an output pot.

[TejfolvonDanone]

As far as i know darlingtons are used mainly in amps because there you can take advantage of their really high current gain.
Maybe you can search for one transistor fuzz/overdrive circuits. Eg: http://www.diystompboxes.com/smfforum/index.php?topic=41342.0

[Kipper4]

Thanks Guys good call.
I also remember the Smallbear little darlington TB

Anything else apart from boosters?

[duck_arse]

learn to luv the fuzz, rich.


also, the ampeg scrambler uses darlingtons, doesn't it?

[samhay]

What do you usually use NPN transistors for?
You can essentially treat Darlingtons like any high gain BJT, but remember that you get 2 diode drops from base to emitter.

[Kipper4]

learn to luv the fuzz, rich.

Maybe one day......
though I guess they are sellers.

What do you usually use NPN transistors for?
You can essentially treat Darlingtons like any high gain BJT, but remember that you get 2 diode drops from base to emitter.

Usually as a space saving device cause I dont want to put another op amp on the board.

So just use the darlingtons in practically any bjt boost/OD and expect no changes except higher gain and a further diode drop in at Vbe.

that simple
thanks

[nocentelli]

Yes, but not just a bit higher gain: the gain of the "two" npn's that make up the darlington are multiplied together, so a standard npn might has hfe of 400, but a darlington may be 10-20,000+ (look at original npn bazz fuss - collector resistor 100k vs version 2 with a darlington and the collector resistor dropped to only 10k).

[Kipper4]

Thanks Leo
I'll do some research and look at that
thanks
I ordered them for a research project. I already have a dozen mpsa14s which according to the data sheet have hfe above 5,000 but as you say the mpsa13s have gains above 10,000.
Maybe i could use them in a bearhug (IIRC) or somesuch too.

[samhay]

If you add negative feedback - e.g. an emitter resistor without a bypass cap - then you can set the voltage gain to something a little more useful (well lower) than 10k.

[Kipper4]

Cheers Sam I'll keep an eye out for that.
Emmitter to base?

[TejfolvonDanone]

What's the point in using a darlington just to decrease it's gain?

[Kipper4]

Cause I bought 50 of the buggers and its a shame to waste em

[TejfolvonDanone]

>Emmitter to base?
Emmiter to ground. Like in the schem from  nocentelli but without C3.

[digi2t]

Crybaby uses it in the first stage.

[Kipper4]

With 50 in stock there's only gonna be one cry baby round here and that's me

Depending on how the research project pans out too.

[digi2t]

With 50 in stock there's only gonna be one cry baby round here and that's me

Depending on how the research project pans out too.

[Groovenut]

Pretty sure you could sub it in for the MPSA18 in Jon's Bearhug compressor