Bias circuit.what.s the clue?

[R.G.]

If one prefers platinum plated to gold-plated, one can diddle the resistors and caps to make, say, -75V and then use a 50V zener to fix the bias voltage without respect to what the ripple voltage is, so HW vs FW doesn't matter. A 51V zener is $0.21 in 1W, $0.12 in half watt.

One could double the cap value in HW, and have the same ripple as FW. A 10uF/100V cap costs $0.09, a 22uF/100V costs $0.15 (today, Mouser, ones)

One could use a capacitive divider; a 47nF to 150nF cap plus a DC restoration/clamp diode added instead of a series resistor gives about the same bias voltage results as a series resistor HW version.

There are many solutions. Cost and durability should be considerations in any design.

[Leo_Gnardo]

Ease off on the caffeine.

Bbbbbut but but but... hold on there a second, listen to this:

Starting cup #4 for today! I'm biased towards caffeine. Even better, now it's a Sinatra Sunday.

[Enzo]

Hey jmaf
Did I do something to you elsewhere? Why the hostility? All I did was disagree on a small point. I am not forcing you or anyone else to agree with me.

I disagreed with your assessment that bias supplies are half wave due to Chinese competition, and offered the Fender pre-China designs as examples. if that was not what you meant, then I apologize, but it was certainly no attack on you, nor meant to be pedantic. This conversation is not something to win or lose.

And while I agree with you that FW offers better results than HW in many situations, I disagreed with you in THIS case, since there is no current draw to create the ripple. Again, you may think i am wrong, but there is no need for personal hostility. I believe I made my contrasting point politely and in civil manner.

[jmaf]

I didn't say you weren't polite and civil, Enzo. I said your comment was pedantic. Nothing personal at all either. According to the dictionary pedantic is something "marked by a narrow focus on or display of learning especially its trivial aspects".

For a Chinese factory adding 2 diodes may be a serious cost, for hobbyists who make a few units a year it is not an issue so just make it full wave if you can. Isn't that what OP asked? Those were my 2 cents about it. I respect you disagreeing with that though, I have no passion for the two lost diodes at all.

[DrGonz78]

I think your both just tubular dudes!!

[The Dude]

I would never play through one of those vintage crappy Fenders. They don't have FW rectifiers.

[jmaf]

I would never play through one of those vintage crappy Fenders. They don't have FW rectifiers.

If you're competing with China, then using half wave means big savings in millions of units.

But if you're building amplifiers as a hobby, a few units a year, paying U$ 2 more for a full wave rectifier doesn't hurt and gives you twice the power and half the ripple, even if you don't need the power at all it's still a superior bias supply.

For the record, I never said what you're implying I said.

[nickb]

Notwithstanding the ripple argument, there may be circuital reasons why a FW rectifier could not be used. Consider a center-tapped HT winding with bias tap. You cannot use a FW bridge here as the CT as it is already connected to ground.

[The Dude]

I wasn't implying anything and the post wasn't directed at you specifically. I was just making the point that, IMO, this thread is "much ado about nothing". Full wave, half wave, bridge, whatever. Any of them can be made to work for this purpose. Half wave rectifiers have been used successfully in bias circuits since the conception of tube amps and there's nothing wrong with FW either. It's a silly argument.

[jmaf]

I wasn't implying anything and the post wasn't directed at you specifically. I was just making the point that, IMO, this thread is "much ado about nothing". Full wave, half wave, bridge, whatever. Any of them can be made to work for this purpose. Half wave rectifiers have been used successfully in bias circuits since the conception of tube amps and there's nothing wrong with FW either. It's a silly argument.

[The Dude]

I rest my case.

[jmaf]

I rest my case.

C'mon man, don't go now. Tell me more.

What's your opinion on avalanche vs Zener effect on triple distilled bias supplies?

[catalin gramada]

I intend to use some nice very low impedance 100uF electros caps. But...have a doubt if have any more sense to replace the last one to better AC decouple with a fast 22uF polyprop capacitor /from a driver load perspective/ .please? Thanks.

Late edit: one more question.please... How imperative is for bias voltage to precise track the plate voltage supply variation in dynamic conditon.please ? Thanks