Parallel Transistors - Night 2

I am not very happy with the way that this schematic looks.  I suppose that if I ponder it a while I can probably find a better way to visualize the circuit.

This is the same basic circuit as what I posted last night using the Java simulator.


We have three small signal NPN transistors running in parallel. I think that you could
drop in a quite a few different parts with similar results. The bias on this is AC
on the base of the transistor. That means that it is only going to turn on for the
positive portion of the sign wave and when it cross zero and goes negative the transistor
is going to turn off. This should run in "class C" since there is no DC bias to the
base assuming that we are dealing with small signal parts.

This circuit is designed to be driven with about +10 to +20dBm with the parts as shown. 
I would expect that the input may need a transformer given that input is likely around
20 ohms depending on the size base resistors used. (Base resistor
/ 3 = Zin)
The output impedance of this is probably in the 200-300 ohm range
so T1 is used to match it to something in the 50 ohm range.

Running in "class C" the current to gain ratio is probably not too bad. Running in
"class A" this circuit would likely be extremely current hungry.


I would like to try to make a board for this circuit and maybe a basic push-pull this

PS... Morning notes:

  • I updated the picture as I had an artifact in thee that I thought that I had moved...
    but I had grabbed the wrong image.

  • I added point of clarification in red
    about the input impedance.

  • It was suggested that I could use three 150 resistors to get a Zin of approx 50 ohms.

  • When I did the software modeling (grain of salt) a 50-100 ohm base resistor looked
    slightly better over all in the circuit with about 10dBm of input drive.

  • During the software modeling (grain of salt again) a 100-200 ohm base resistor looked
    slightly better over all in the circuit with about 20dBm of input drive.

  • It will likely be either a transformer on a T50 size core or a base resistor of 50-200
    ohms either solution is cheap and easy depending on my mood and how it plays in the
    real world. (50-200 ohms will probably not play much differently. It is more likely
    going to be dependent on what parts I have on hand. I probably have 47, 51, and 100
    ohm parts in bulk but probably not many or any 150 ohm.)