FET Replacement Question

[Richard Solomon]

I feel it's better to ask than guess, especially at $110 a pop !!

When installing the new FET, the cross-piece gets screwed down and a small piece goes
between the cross-piece and the ceramic part of the FET. It has a set screw that holds
the small piece.

What is the installation procedure ?

Do I tighten down the two screws in the cross-piece first, then tighten down the set screw?
Or is it a case of going back and forth between the socket head screws and the set screw ??

When I removed the blown FET's, the two socket head screws were quite tight, but not such
that a small right angle socket wrench couldn't remove them.

Thanks for any tips.

73, Dick, W1KSZ

[Warren Stone]

When installing a new FET, clean out the old heat sink grease with isopropyl alcohol and a cotton swab.  Install a very thin layer on the new FET.  Do not solder it yet!

Loosen off the set screw above the FET.  Adjust the FET to the correct position with the RF input and out traces.  Torque down both sides to 4.5 pound inches.  (This what the Larcan supplied tool is set for.)

Now tighten down the metal cap above the FET with the same torque.  Be careful to keep the smooth side against the FET.  The set screw will cause scratches that could damage the FET if the cap is put in upside down.

Once tightened down it is time to solder the four tabs in place.

Turn both bias pots fully to zero so there is no bias current.  Power up the amplifier and adjust bias current to 500mA.  Now is a good time to confirm and adjust to 500mA bias current on all FETs.