amdx wrote:
Hi all,
I finished the amp that had the 5 Ghz transistor, I changed it to a slower
one.
The objective of this amp is to cause minimal loading of the circuit it is
measuring.
When I install the box cover the voltage gain drops by 7%, so I think the
input capacitor
plate is being loaded by the cover.
The input capacitor plates can be seen here;

http://i395.photobucket.com/albums/p...mspaced5mm.jpg

The plates are 1 cm x 1 cm spaced 5 mm apart.

I have thoughts about rectangular plates 0.25 cm x 4 cm to get more
distance from the top cover, (and the bottom.)
Or a real gimmick cap where I twist a couple of 39 Gauge wires together and
attach opposite ends to input and output.

Any ideas to minimize input capacitance to the box?

Here's the amp in box.
http://i395.photobucket.com/albums/p...erampinbox.jpg

This is the original circuit page with schematic;
http://www.crystal-radio.eu/enfetamp.htm
Thanks, Mike

PS, I was having trouble getting some close-up pictures, I grabbed a
magnifying glass and took some
pictures through that, works good.


Response before looking at others:
1. use one 10Meg and connect it to source OR cap bootstrap the 10meg
input divider to the source.
2. "wrap" a shield around the input wire & plate and drive the shield
from the FET source or T2 emitter.
3 What the heck is that HUGE block attached to the input plate?
Ditech it; you will see a significant decrease in input capacitance.