Running this as class A is really inefficient but this is what I roughed out. The output is just starting to clip at the input level shown.

What kind(s) of transistors are you using in your sim?

 

I used what the OP used in his schematic... 2N3700's.

 

I've since updated the schematic text data to reflect the transistor models. BTW, I doubt that I would have approached the circuit in this way if I were doing this for myself. Since the OP doesn't need a broad band amp I would have built a tuned amplifier. With tanks I wouldn't need 50Vcc. Cool things happen with resonant circuits, including transformer action.

 

I am so sorry guys. I didnt get an email from the forum in a while so assumed that there were no replies. Just thought I would check in case! So very sorry for being quiet for a while! I will give your posts a more thorough read later and get back to you. Thanks all.

Just regarding the last post.. how would you have gone about the design? I am a beginner, so any feedback or ideas is really appreciated!

Thanks again,

Mark

 

Ok.. have had a little time!

Am using class A purely for simplicity. power efficiency is not an issue. however, if you think there is a better option, please do say! i just figured that a push pull would require a more complex design and also for speed, i need to keep in the active region..

that sim looks very promising! i will try to get it running myself so i can investigate it a bit more.. i think that having got the CE working, i didnt want to break it by changing all the values.. but perhaps building with the CC from the start makes more sense. thank you for taking the time to do that.

as far as a tuned amplifier goes, how would i go about doing this? I know how to find the L and C from the frequency, but this sits towards the top of my voltage swing. using a larger Re has made the gain smaller so that it is not distorted, but i cannot get it at a lower average point. what is the advantage of a tuned amp over my solution? is it more efficient?


what exactly do you mean by transformer action?

Thanks again for your help!

Mark

 

Me again..

I have had a change to replicate your circuit and managed to get it working, as you showed. Thank you so much!

I was just wondering if I could ask the following..
What would be the advantage of using a cascode amplifier? If, indeed, there is one?
With a tuned circuit, would you have a series capacitor and inductor in parallel with the 820 ohm CE load resistor? How does this work to benefit the efficiency?
And what is the transformer action you mentioned? Is it good?!

Thanks again!

Mark

 

Me again..

I have had a change to replicate your circuit and managed to get it working, as you showed. Thank you so much!

I was just wondering if I could ask the following..
What would be the advantage of using a cascode amplifier? If, indeed, there is one?
With a tuned circuit, would you have a series capacitor and inductor in parallel with the 820 ohm CE load resistor? How does this work to benefit the efficiency?
And what is the transformer action you mentioned? Is it good?!

Thanks again!


Mark

Been a long long time since I've played with resonant and cascode amplifiers. In fact, the last one I built for 20 meters was a cascode preamp using two 6CW4 miniature vacuum tubes. I still have it 35 plus years. They were just a bit larger than a T05 transistor.

Anyway, as I remember cascode amps exhibited exceptional stability from breaking into oscillation. Building a resonant amp is quite an undertaking for a nube though. Resonant circuits have the advantage of taking the most horribly distorted waveform and making it a perfect sine wave, which is why the amps can operate class C, if enough drive is present.

 

Thanks for your reply!

I see. So no particular need for me to look further into cascode i hope.

Yes, I think that perhaps a tuned amp is a bit above my ability! Although if it would provide a better sine wave, I may try to look into it a bit. I am not sure I can move to a class C, because I think that turning the transistors on and off would be too slow.. Is there an efficiency benefit of using a tuned load on a class A, or would it simply be cleaning the sine wave?

What do you mean by if enough drive is present?

Thanks for all your help!

Mark