Hello, I am building a small QRP amplifier for HF and I was wondering if there is any common transistor more powerful than pn2222 in the same small plastic case (TO-92)?
A PN2222 has a maximum allowed collector current of 600mA. That is for continuous DC that has no frequency. At 100MHz its minimum current gain is only 2.5 which is not much better than a piece of wire.
A PN2222 has a maximum allowed collector current of 600mA. That is for continuous DC that has no frequency. At 100MHz its minimum current gain is only 2.5 which is not much better than a piece of wire.
A 2N4401 is another "general purpose" transistor, not an RF transistor. Its typical gain-bandwidth product is 250MHz where it has no current gain like a piece of wire and at 25MHz its typical current gain is only 10. Its minimum frequency or minimum current gain is much less.
I have seen some TO-92-like cases which have an itty
bitty "power tab" sticking out, presumably to help with
thermal impedance (you might even be able to solder to
a better sink). But why is TO-92 so important, while other
can and tab styles aren't considered?
You can also, I believe, find press-on heat sinks for TO-92
devices which will at least improve upon free-air heat
throw.
You want a fT which exceeds your desired forward gain
times signal frequency.
I have seen some TO-92-like cases which have an itty
bitty "power tab" sticking out, presumably to help with
thermal impedance (you might even be able to solder to
a better sink). But why is TO-92 so important, while other
can and tab styles aren't considered?
You can also, I believe, find press-on heat sinks for TO-92
devices which will at least improve upon free-air heat
throw.
You want a fT which exceeds your desired forward gain
times signal frequency.
I parallel multiple transistors (10 of them) to make a class-A 1W HF amplifier, so you can get an idea of the circuit I am working on.
Heatsinking is done by a small fan, blowing forced air to the transistors. This is lighter, smaller size and cheaper than a huge heatsink required for class-A for the heatsink-requiring packages. I have managed to make a class-A 1W HF amplifier using 10 2n4401 and 15R emitter resistors, with about 40mW input. All harmonics are -40dbc. I think it is a good setup.
I am looking for these TO-92 because they are generally cheap, 10 of them are the same cost as a big 2sc2166 (which did not gave a better performance).
What sort of Ft should I look for, for the 1-30MHz range? Should I look for an Ft in the UHF range?
Like for example the 2sc9018 Ft 700MHz min Ic 50mA???