Biasing combination bias

[jpfamps]

OK so what have we gotten from this so far? Let's see:

1) Bias is bias, whether it is fixed or combination (though I HAVE, in the case of the aforementioned '68 chassis Fender's, saw negative harmonic effects on a sine wave, which was also palpable when checked with speakers with a guitar; it was a bit cold and ugly-sounding).

Did you trying removing the 5uF cap between the cathodes?

[R.G.]

1) Bias is bias, whether it is fixed or combination (though I HAVE, in the case of the aforementioned '68 chassis Fender's, saw negative harmonic effects on a sine wave, which was also palpable when checked with speakers with a guitar; it was a bit cold and ugly-sounding).

Bias is bias for power dissipation issues. The degree of bypassing on cathode resistors does have a measurable effect on distortion, with distortion rising if you omit the cathode bypass capacitor. So your observation is correct.

2) There is NO 100% failsafe biasing system. Perhaps the best bet would be UNBYPASSED cathode-biasing, leaving the possibility of the capacitor shorting out of the equation.

That would be safest for cathode biasing, although it does introduce the distortion you found. Actually, it is entirely feasible to put a current monitoring system on the output tubes and have it sense the current (including averaging over some time period to eliminate transient issues) and shut things down when an over-disspation situation exists. I've built such a system and it works.

3) "Magical" designs are usually nothing more than tweaks, and everyone seems to have their own version.

Yep. Magic is personal - it exists only inside a human head, and it's different in each one.

4) Goat cheese doesn't seem to be very popular on this forum. I happen to love it.

So do I.

[R.G.]

I liked goat cheese until I went on a field trip with my son to a farm. As it turns out, goat cheese smells just like goats. I don't enjoy goat cheese nearly as much as I used to.

Just like the old saying - if you like sausage and respect the law, don't ever watch either one being made.

[Enzo]

Goat cheese is OK, as long as it isn't very "goaty." Billys really do stink though. It sticks with you.