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QRP HF amplifier schematic needed

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neazoi

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Hello I am building a QRP (CW) transmitter tor the HF bands 160m to 10m and I need an amplifier to drive my oscillator so I can get 1-2W max out.
I have found this circuit **broken link removed** (picture at the bottom) and I have built the oscillator but I need to eliminate the interstage transformer (capacitive coupling)

I have managed to eliminate the transformer on the oscillator but capacitive coupling does not work at the input of the amplifier.

I was wondering if you can suggest something for correct capacitive coupling (or another amplifier circuit)

Note. I have tried different base, collector, emmiter biases but the amp does not give output power at all! The transistor is new.
 

Using a transformer means you get inductive coupling, and not capacitive coupling.

Using just capacitors, without any inductance, you lose the interstage impedance matching. That means you are losing power.

So, there is a possibility to eliminate the transformer, with an LC matching network.
 

if you use different switched capacitors for the different hf bands you should be able to compensate with impedance matching with low power losses I think?
I managed to drive a 2n2222 power amplifier with this oscillator using cap-coupling. the extra 2n2222 gave me about 50 (worst) to 170mw (best) throughout hf. maybe the transformer coupling in the original circuit performs also some voltage step-up so it can directly drive the 2n3553 amp without the need of a buffer stage?

have you got to propose any cap-coupled circuit for hf?
 

Using just capacitors (or just inductors) for matching, is valid only for impedances which have particular real part.

You can use a simple Γ or an L network for the matching (the net, or the RF books are full of examples), but you have to know somehow the source and load impedances.
 

Thank you.
I have managed to make it work on 40m to 10m bands on the 2n2222 only. on 6mhz it does not aoutput any signal and on 4MHz the signal is again ok.
Is there any case that the amplifier stops to operate at a point between two other operate points? I thought that the amplifiers have a frequency range and they do not do any glitch (stop band point) through it.
sorry for my english
 

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