Building with Mosfets

[markbul]

I ordered some Mosfets to use in amp builds "Mosfet Follies" style. What would be the best way to integrate a mosfet into an eyelet board build? Those leads are a liitle too close together. Any concernes about soldering them? They came in an electrostatic bag - do I need to de-louse myself before touching them? :D

[Steve Conner]

Most MOSFETs you get nowadays are fairly tough against static. I build dozens of prototypes of things using MOSFETs and CMOS chips at work and I've never zapped anything. But I still wouldn't do anything dumb like rubbing the transistors with a cat while wearing nylon underwear.

I think the easiest way of integrating them is to solder longer wires onto them. Having said that I once built a hybrid amp that used tubes, MOSFETs and ICs. I mounted all the silicooties on a piece of stripboard (the stuff that has a grid of holes and copper stripes underneath) that I screwed to the chassis next to the eyelet board that held all my sensible-sized tube components.

[R.G.]

The longer wires idea is good, but there are some things you need to do to keep them running.

- Solder a 100R to 1K resistor in series with the gate lead right out at the MOSFET package. Otherwise, you may be transmitting VHF or UHF radio and not know it.
- If the device does not have an internal zener diode, add a gate-source zener again, right at the package.
- Cover the wire-MOSFET joints with heat shrink, including the gate stopper resistor.
- Be sure you insulate the tab from chassis ground. It will most likely be at about B+. Sil-pads are easiest, coupled with shoulder washers.

[markbul]

The part is IRF820B Fairchild Semiconductor - I don't see anything about an internal zener. What kind of zener would it take?

[R.G.]

Get a 12V 1/2W zener, any kind, there are several type numbers for this. Hook the cathode/bar to the gate, the anode/arrow to the source. In the forward direction, this lets the gate go up to 12V higher than the source, good for many amperes in the channel. In the reverse direction, it's clamped to -0.6V.