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The 2N4427 works very well here, but is obsolete.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.
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
Hi Rickard. In my area 2N2369A are fairly common, inexpensive, and also have an even cheaper local equivalent, KT3142A. I successfully used it as a driver for either IRF510 (<= 14 MHz) or RD15HVF1 (<= 30 Mhz) in several recent transceivers, both SSB and CW ones. Another option could be 2SC3953, but it has fT = 400 Mhz vs 500 Mhz for 2N2369A / KT3142A. Finally, I tried 2SC5694, but it didn't work well in my typical circuits.
ReplyDeleteOoops very sorry for the typo! 73s de Alex, R2AUK
ReplyDeleteHi Alex
ReplyDeletethanks for the info. I'm sure it will be useful to many people.
73's
Richard