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Saturday, 29 January 2022

General Purpose Transistors in RF Amplifiers

I noticed the availability and cost of transistors I had previously used had become an issue. I decided to test a range of low cost widely available transistors to determine what might be suitable. 

Output stage

I left the output stage as a through hole part because heat sinking a 1W Class A transistor is difficult with a surface mount part.

Driver 

The 2N4427 works very well here, but is obsolete. A SOT89 package looked suitable for the 230mW of dissipation and numerous transistor choices wer available.

Pre-driver

The 2N2219 I had previously used was very expensive now if your junk box lacked any. Seemed complete overkill for a stage delivering 5dBm so a SOT23 package was decided upon.


PCB's were fabricated which would allow me to systematically try alternative transistors and test output levels, gain and frequency response.

Stage            Original       Version 1    Version 2    Level

Pre-driver    2N2219        2N2219        SOT-23    5dBm    Very expensive

Driver           2N4427        SOT-89        SOT-89   15dBm    Obsolete, but good if you have one

Output           2SC3230     TO-220        TO-220    30dBm    Obsolete now.  

 

 

After a record heatwave last week (6 days of +38 degrees) I'm about to endure another hot weekend so progress will be slow. But as test results come to hand I'll post them.

73's

Richard