General Purpose Transistors in RF Amplifiers - Last Ouput Transistors Test

After testing some more transistors I found the 2SC4552 delivered 0.9Watt in my class A test amplifier at 3.6MHz. I am confident that a little more standing current and this transistor will deliver 1 Watt and it appears to be quite robust at this power level.

However, there are drawbacks:

• the input impedance of this stage is around 20 ohms at 3.6MHz. Increased current will see this fall further
• The efficiency is low with the transistor dissipating 3W's.
  
• at 20MHz the output had dropped to less than 100mW's
•  a unit price of $1.50 is approaching the lowest cost RF mosfets I can buy. 

So it's not the solution I had hoped for.

Nor have I found a suitable general purpose transistor that can work in a 1 Watt Class A HF amplifier. It's time to move on to an alternative approach.

 

Next Steps:

Investigate if parallel transistors will meet the 1 Watt target. 

Investigate if a 2SK3078A or 2SK3756 can be made to work at HF.

Consider a single ended Class AB final stage in the amplifier.

73's

Richard