Q70 replacement

Tom Cooper

Q70, the audio pre-amp, has a really big job in the uBITX and sometimes gets overdriven by very strong signals. Plus, since i replaced the 2822 audio amp with an LM380 I've lost 8db in audio gain.  I wondered if another transistor would improve this.

I have some 2sc945 transistors marked with the highest "beta"(AKA hfe) rating, so I took one with a 360 hfe and replaced Q70.  I made no other component changes.  The 2sc945 is supposed to be specially designed for audio pre-amps, so it should be good.

The results are totally positive.  I have more AF gain, the IARU HF contest could not overload it and I did not burn myself with the soldiering iron or drop molten solder onto my bare legs.  

If you are not needing more AF gain or not hearing any overload distortion, then this mod may not be for you.  If you are, it works for me.



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