An illustrated guide to building an F5

Amp biased fine and sound comes through speakers.

Only problem I had is I accidentally adjusted P3 and now both are out of whack.
I had the trimmer centered before installing.
Any recommendation of how to center them by measuring with DMM or should I just count the turns to get them equal?
The resistance between pins 1 and 2 and pins 2 and 3 should be the same.
+1 to both...

Measuring accurately to the 10th of an ohm between the two may not be the easiest. Try a few turns and see what it does for your own knowledge. If you find that too many turns has too little a change, and you're still worried, count turns from click to click and center.

Also adding to the previous... if you can't get to the bottom of the board, or just don't want to since they're mounted already, measuring across R3 and R4 is an option.


Paid Member
2005-08-02 10:47 pm
Anybody know a source for IRFP240s and '9240s?

I fried R13 on the left channel. I got a little hasty and careless while doing the biasing back-and-forth, and watched in horror as my meter showed 1V, rapidly climbing. Then smoke, so I shut it down. Fuse didn't blow. Right channel plays fine, so I'm anxious to hear the stereo version.

:cautious: :love:

I've had the F4, F6 (stock, not DIY) and Aleph J, so I'm kind of working backwards vis-à-vis other folks' order of selection. So far, the F4 is king, but it's also a PITA if you don't give it enough voltage swing.

Edit: forgot my ACA, which I'm thinking of upgrading with some IRFP150s. Big assumption there, "upgrading".
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Depending on how many you want... whether you want them matched... enough to match... etc...

The store here.
Swap meet here.
One of your other amps :oops: is a great resource if your normal places are out of one or the other and/or if you're looking for a manufacturer other than Vishay.
Mouser (but with a short wait)