Using BFR193 RF transistors in an audio amp introduces some interesting behavior! They will happily pick up stray high frequency (they are good to 2GHz) RF from even very short wires and amplify it quite a lot. I am running the first stage at nearly 35dB of gain at audio frequencies. When this UHF RF is damped, however, they are very quiet and sound very good. Quite a lot quieter than the general purpose transistors I previously used! #HamRadio #AmateurRadio
Discussion
Loading...
Post
Here's an AC voltage gain comparison of my BFR193 + 2n3904 amp vs the Soldersmoke 2n3904 amp. This is Qucs-S as I don't have a scope and can't measure the real thing. But you can see the hugely flatter response across the SSB voice frequencies and the much higher AC gain (this is dB).
Chart showing the AC voltage gain from my (EI9ITB) 3 transistor amplifier.
Chart showing the AC voltage gain from the Soldersmoke 3 transistor amplifier from the direct conversion receiver.
Note that the Stage3 line is not accurate as I could not isolate it from the collector bias. The total and first two stages are, however. In real life the volume difference is less than it looks like. I suspect that the work that I did to dampen oscillation in the Soldersmoke amp is returning better performance than this.
But there is no doubt that the BFR193 massively outperforms the 2n3904 at low signal levels. Look at that first stage gain.
bonfire.cafe
A space for Bonfire maintainers and contributors to communicate
Automatic federation enabled