I dont think thats right....

[Alpha579]

Hey all,
I was 'aving a go at a single stage Mosfet booster, as there ment to be quite high gain, and i got as far as getting 6.5db out of it??? Im using a 2n7000 Fet, and the schematic is here (bottom of the page):http://www.geocities.com/alphaeffects/
all help apprieciated!
ps.
the pins of the mosfet are as follows:
G:4.5v
D:4.766v
S:0.0622v

[Peter Snowberg]

For testing purposes, you might want to try a pot (50K to 500K) instead of the fixed divider to set the bias.

Connect the element across power (CCW end to ground and CW end to +9), and then attach a 1M resistor from the wiper to the gate. To lower the noise a bit, add a cap from the wiper to ground.

See how things respond with the bias at different voltages.

Take care and best of luck,
-Peter

[Boofhead]

Something looks wrong alright.

The bias is wrong and the MOSFET should be turned on hard, you should be seeing a Drain to Source voltage difference of nearly 0V.  The gate to source voltage is in the 4V region that is normal when the MOSFET is hard on, which is should be according to the values you are using but it's not so there's one problem already.  When the MOSFET is biased properly (not hard on) the gate to source voltage should be more like 1.9 to 2V.

Assuming you fix the previous error.....The 1k source resistor is too small to provide a stable bias point with a 68k drain resistor   Shouldn't be less than 3.3k or so - in that case you upper 1MEG bias resistor will need to be around 3.3MEG but the bias still isn't well defined.   More preferable is a 10k source resistor and a 2.7MEG bias resistor to +ve.   Perhaps better again is to drop the drain resistor to 10k, use a 1k source resistor and a 2.7MEG bias resistor to +ve.  Larger source resistors will define a better bias point.   These are only a rough guide you might have to go up or down a value.