EMRFD Message Archive 11911
Message Date From Subject 11911 2015-11-26 09:42:50 bob_ledoux Question: What SMT Transistor for Post-Mixer Amp
The 2N5109 was commonly used as a post mixer amp at HF frequencies. It was powered with lots of current to preserve dynamic range.
So what SMT transistors are being used for the post mixer amp function?
11912 2015-11-26 11:03:04 K5ESS Re: Question: What SMT Transistor for Post-Mixer Amp
Here’s a link that discusses an SMT replacement for the 2N5109 if you haven’t already seen it.
11914 2015-11-26 12:25:33 kb1gmx Re: Question: What SMT Transistor for Post-Mixer Amp there are a number of devices that will function well in the usual resistor feedback circuit.The criteria are:CATV types.1 to 2.5W dissipation capability.Good gain at high current 40-60ma12V (or slightly higher part)Low noise, sub 2db is adeqate for HFFT greater than 500mhz.One such part I've used is the 2sc3356 or 3357 (or the CEL/Renasis part of the same flavor).There are plenty of choices possible.When using SMT versions, remember the board and its pads are the heat spreader/radiator.So design accoringly, or take reference from the data sheet.Allison 11915 2015-11-26 13:56:20 vasilyivanenko Re: Question: What SMT Transistor for Post-Mixer Amp
Thanks Allison, great suggestion: I too have found that the 2SC3356 works great in that slot -- also I've plied and characterized:
Without appropriate collector heat sinking -- for sure, they'll run away and stink up your lab
11916 2015-11-27 05:16:24 i7swx Re: Question: What SMT Transistor for Post-Mixer Amp
I have used BFG135, BFG97 and BFG67 for RF amp without any problems. Noise Figure is not reported but for the BFG67 is 1.3dB at 1GHz and 2.2 at 2GHz, so the others should not have too much different NF.
As heat sink I have used bronze thick nuts soldered
11919 2015-11-27 08:01:32 John Harding Re: Question: What SMT Transistor for Post-Mixer Amp Why not look at the Clifton Labs Norton Amp - all surface mount. Earlier versions had thru hole.Happy Holidays