Tuesday, April 19, 2016

Dual gate MOSFET amp prototype.(BF2040W)

I put a 5 Volt regulator on  the board. In the upper right corner the green is the filter capacitor. The strip closes to the front is 0 Volts. The next strip is 1 Volt. I have a square around the transistors which is ground. The next strip is 4 Volts. The top strip is 5 Volts. I'm feeding the board with 9 Volts.I have the dip meter feeding the input with about 1600 Khz.

 The scope is reading the output of the last stage. pretty good signal.
I used two 10 KOhm and a 22 KOhm to make the voltage divider so it isn't "dead on" but close enough. The 1 Volt bus is 1.19 Volts.

 The 4 Volt bus is 3.83 Volts. If the designer wanted he could use a pot instead of fixed resistors but I think it's close enough. Time to find out. I put the coil I made in the unusual IF post and a ear phone on it and lots of rush hissing in my ear. I used a screw driver as a core to adjust and I hear a weather report. I waited for the station ID and it was WWL New Orleans. I ask google and he said I am 135 miles from them. Not to bad my antenna is a test lead clipped to an AC duct.

Close up of the amp. I have the parts spread out so it's easy to work with. I'm using inductors in the drain circuit and capacitor coupling. The five blue things in the middle are 8.2 nfd caps. I'm thinking I will replace them with 10.7 Mhz resonator and have an IF strip. The circuit works but I probably should put some decoupling caps in it.I posted this picture so you can see my use of copper foil (found in the stained glass supplies) and head pins (found in the jewelry making supplies). The foil provides a bus to solder to and the pins can be used for wire wrap and clipping test leads.


  1. Hi, very interesting work. What precautions, if any, you took when mounting the mosfets? I am talking about ESD. I tried something similar and so far none work but my guess it was ESD or my Sencore tester voltage was too high for this model of dual gate mosfet.

  2. Replies
    1. Well I say no special precautions. My habit is to use as little time as possible to make a solder joint. I prefer a hot iron and short work time. I use tweezers to place the components. I have been told to place both hands on the bench or a piece of equipment (power supply chassis or computer). Sometimes I worked is a shop that required us to wear a ground strap on our wrist but i never was a fan of the strap.