An illustrated guide to building an F5

[6L6]

Originally Posted by merlin2069er

But my left is way out of wack. I'll attempt to look at the board closely to determine if I've mixed up any resistors, hopefully I can check these values with a meter.

Any suggestions?

Let's assume that you haven't mis-wired anything on the the left, as you are getting legitimate numbers. It still won't hurt to look, however!

On the left channel, what is the max bias can you attain with zero offset?

[merlin2069er]

Ok, I'll give that a try tonight.

Thanks.

[merlin2069er]

ok, this is what I've attempted...

I've adjusted my left channel to ~ .004v dc offset after an initial few minutes of tweaking.

I had to adjust the voltages @ 1.284 v dc & -1.279v dc (across the .47ohm 3 watt resistors)

It definitely heats up quicker... I'll check it again at 30 minutes and 1hr.

That's more that 2x the .59v dc the service manual suggest to bias the amp at.

Any suggestions, or is this fine?

-----
I've checked it at ~ 30 minutes, and the heatsink is quite hot. I can leave my hand on it for 5 seconds or so.
It's 2x as hot as the other heatsink...
-----
I've turned it off just after ~ 40 minutes...

[6L6]

Huh...

Turn your pots all the way down and try it again. Can you, for instance, bias to .2v with zero offset? If so, then try for .3, and then .4, each time attempting to keep the offset to zero.

[merlin2069er]

ok, I'll turn the pots all the way counter clockwise until they click and try again tomorrow.

I might have adjusted the pots too quickly to begin with...

[6L6]

If everything is wired up correctly and you got that much bias, there is no doubt that you are well, well past the rated dissipation of the output devices. You have the 4U x 400mm heatsinks, right? You should be able to leave your hand on them indefinitely. It is more than enough heatsink. The fact that you could only do 5 sec means that something is wrong. Hopefully it's only a wrong bias adjustment.

Turn the pots all the way down until they click and start over.

[merlin2069er]

ok, got it!

I reset the pots to 0hms, and powered it up.

adjusted each pot and looked at the offset. As you adjust one pot, the offset grows larger, by adjusting the other it takes it back down to ~ 0v.


So after a few minutes I got ~ -.005 v dc

.536 v dc & -.537 v dc.

I'll leave it on for another .5 hr before I get to bed...


I melted my a pair probes on one of the resistors... at the higher bias.

[merlin2069er]

I just have to finalize a few things...

Can anyone recommend speaker binding posts for the F5?

I'm going to have to pick up some speaker wire too, maybe 10 feet.

[merlin2069er]

Whew, finally done with my final touches...

Here's a link to my quickie video clip.

f5 amp

[6L6]

Awesome!!!

I especially like the thick faceplate. And that we have the same DMM - the fluke in the center.

Can you post some pics here?