BF822/MJE250 substitutes ?

[KrammeAcoustics]

Hi forum

I want to build this simple construction. I want to use 2SJ50/2SK135 Mos-Fet's instead of IRFP240/IRFP9240 ( i hope it's possible because i've got those in stock ), but i don't have (NPN) BF822 and (PNP) MJE250 in stock, so it would be nice, if it's possible to find "more well known" substitutes for those. I would also like the BF822 substitutes, to be in TO-92 housing, if it's possible.

Please list some substitutes, thanks.



NOTE: Yep, it smells like a simplified ver. of the amplifier, shown in the last number of Elektor Electronics ...correct !

[Tekko]

MJE340 and MJE350 i think.

And that circuit as is would only work with laterals, for the irfp's stated, your gonna need a bias transistor attached to the heatsink to compensate for thermal runaway.

[KrammeAcoustics]

Originally Posted by Tekko

MJE340 and MJE350 i think.

And that circuit as is would only work with laterals, for the irfp's stated, your gonna need a bias transistor attached to the heatsink to compensate for thermal runaway.

UPDATE: I've just found a couple of MJE251 and it seems they should be able to replace MJE250.

But i still need substitutes for BF822

Tekko, please explain, i thought SJ50 and 2SK135 ( I were intended to use instead ) is laterals ?
...but maybe i've been misunderstanding something:
sub for 2sj50/2sk135

[Tekko]

The schematic says IRFP240 and IRFP9240, these are vertical fets.

But yes in think that 2SK135 and 2SJ50 are laterals, but im not sure.

Im only familiar with the ACD100NSD and the ACD102PSD laterals.

[HighTec]

KrammeAcoustics,

before you turn that 'amplifier' on, I suggest you to wear protective glasses cuz I have a feeling it might produce a big bang!

[tom31415926]

Hi,

I don't see a path for DC bias current into the base of the right-hand transistor of the diff pair. No DC current will flow through the 47pF capacitor and the NPN transistor must have some base bias current.

What might be used here depends on the application. If this circuit is embedded in a larger feedback loop, then the base of the right-hand transistor could be held at same bias voltage as the input (the arrow is the input). I suppose a differential input could be derived.

You could create a local feedback loop if you connect the output to the base of the right-hand transistor of the diff pair, but you would need a level shift. No matter what, some attention to DC bias is required in order to see this amplifier work.

Hope this helps.
Tom

[Tekko]

Yeh the circuit is missing the entire frontend, i just assumed he was only showing this part in purpose of finding subs for the transistors. And the 15k resistor can be replaced with a transistor with the base tied to ground.

[jaycee]

Agreed the diagram is only part of the story - it is a typical "complimentary" VAS and output stage, designed to be driven by a long-tailed pair input circuit with feedback.

[KrammeAcoustics]

Tekko, HighTec, jaycee and tom ...you're right something is missing, even i can see that now. This schematic needs some polishing !

[jaycee]

Should look akin to this http://www.ampslab.com/Images/lm60/lm60_schema.gif