"Class A" nonsense

[Old Tele man]

h-m-m-m-m-m...the more I think about it, the more I think you're right, and I'm wrong...and, yes, I had (oops!) resistive loads in mind.

...now that you kindly "...turned ON the lightbulb..." for me, I recall how the downward plate "swing" (voltage & current) travels along the projected reflected load line (downward right, toward cutoff) courtesy of the OT winding inductive "flywheel" effect.

...the idle "point" is where the DC-load line (almost vertical) crosses the reflected AC-load line (horizontally rising toward the left).

...yes Sir, I deserve todays' "Dunce Cap" and shall proceed to the corner and sit in humility...repeating to myself "...it's inductive loads versus resistive loads..." a thousand times (ha,ha).

...I stand (sit?) corrected (admonished?)!

[Merlinb]

So does that mean the matter is settled then? There is design Class, and operational class. You push something beyond its design Class so that it temporarily operates in a different operational class.

That being the case, a single-ended audio amp can be Class-B, but only if someone deliberately designed it that way. For some crazy reason.

[tedmich]

Human constructs can have sharp definitional boundaries, but if they are actually physically manifest, this becomes exceedingly difficult to do. Thus theoretical amps can be in strict classes, but as Merlin has pointed out, once you build them and use them they tend to blur these necessarily superficial definitions. Few (if any) concise definitions can fully describe any actual physical construct. Such simplifications often work in theology, and then only because the subject matter is intangible and the analysis is necessarily incomplete. Many people require such certitude to feel comfortable, for whatever reason, and it is best not to debate them, IMHE.

Nice to know what the simplified amplifier class models describe though!

[Old Tele man]

...we humans are rather ingenious lot, which is why:

1) a butter-knife is often used as a screw-driver...
2) a high-heel shoe is often used as a hammer...
3) a Class-AB amp is often 'called' Class-A for better sales potential.

...it all depends upon how much someone cares to "fudge" the items' real intended (design) application...and, not upon the success/failure of the not-as-designed mis-application.





...I'll be quiet now, because it's sorta difficult to talk with my foot in my mouth (wink,wink)!

[balijukka]

What if...

What if you have a 4 tube push-pull amp with two pairs of different tubes.
B+ low enough that you can run pair in class A all the time, but then bias the other pair so cold that it is class AB.

What do we call the amp as whole ?? - other than a mongrel.

jukka

[R.G.]

What if you have a 4 tube push-pull amp with two pairs of different tubes.
B+ low enough that you can run pair in class A all the time, but then bias the other pair so cold that it is class AB.

What do we call the amp as whole ?? - other than a mongrel.

jukka

We call it "Holy Crap, Batman! Let's go to the patent office!" if we're Randall Smith.

I believe you just almost reinvented Simul-Class (tm).

[Enzo]

You call it an anomaly which has no standard designation.

[balijukka]

...and you think you're so clever and classless and free...

jukka

[Steve Conner]

"As far as the laws of mathematics refer to reality, they are not certain; and as far as they are certain, they do not refer to reality." Albert Einstein

Substitute "amplifier classes" for "mathematics" if you like.

[imaradiostar]

We call it "Holy Crap, Batman! Let's go to the patent office!" if we're Randall Smith.

I believe you just almost reinvented Simul-Class (tm).

Man...you beat me to it. I was gonna make that joke.

jamie

[raiken]

What if you have a 4 tube push-pull amp with two pairs of different tubes.
B+ low enough that you can run pair in class A all the time, but then bias the other pair so cold that it is class AB.

What do we call the amp as whole ?? - other than a mongrel.

jukka

That is called "Extended Class A" operation, as described in RDH4 (no doubt where Smith "discovered" it...)

[Old Tele man]

...from page 587 of RDH4:

"(ix) Extended Class A

Extended Class A is the name given to a push-pull amplifier using a triode and a pentode in parallel on each side. The amplifier operates entirely on the push-pull triodes at low levels, with the pentodes (or beam power amplifiers) cut off; at high levels the output is mainly from the pentodes. Consequently there is some curvature in the linearity ("transfer") characteristics at the transition point. The total dissipation is, however, only about one third of that of a Class A amplifier with the same maximum power output (Ref. E31).

This principle might also possibly be applied to any Class AB or Class B amplifier merely to avoid current cut-off in the transformer and its resultant parasitics (Ref. E13) unless one with very low leakage inductance is used."

...makes one wonder what "novel" difference Randall Smiths' Simul-Class™ has to merit a Patent?

[mooreamps]

the pentodes would have to be biased closer to Class B, if they are supposedly at cut-off, with no signal condition and/or low signal condition.

-g

[Old Tele man]

the pentodes would have to be biased closer to Class B, if they are supposedly at cut-off, with no signal condition and/or low signal condition.

-g

...from the "Claims" statements of U.S. Patent 4,593,251, dated June 3, 1986:

"1(c). first input impedance means coupled to one said pair of electron discharge devices for causing said one pair of electron discharge devices to operate in Class A; and...

1(d). second input impedance means having a lower impedance than said first input impedance means coupled to the other said pair of electron discharge devices to cause said other pair of electron discharge devices to operate in Class AB,..."

"11. An amplifier as set forth in claim 10 wherein the input electrodes of said one pair of electron discharge devices have a fixed bias thereon substantially less than the fixed bias of the input electrodes of said other pair of discharge devices."

...looks to me like an UL OT with the two outer pentodes strapped as triodes using the 43% UL taps and lower bias voltage, while the two inner pentodes use the full OT windings and higher bias voltage.

[mooreamps]

...from the "Claims" statements of U.S. Patent 4,593,251, dated June 3, 1986:

"1(c). first input impedance means coupled to one said pair of electron discharge devices for causing said one pair of electron discharge devices to operate in Class A; and...

1(d). second input impedance means having a lower impedance than said first input impedance means coupled to the other said pair of electron discharge devices to cause said other pair of electron discharge devices to operate in Class AB,..."

"11. An amplifier as set forth in claim 10 wherein the input electrodes of said one pair of electron discharge devices have a fixed bias thereon substantially less than the fixed bias of the input electrodes of said other pair of discharge devices."

...looks to me like an UL OT with the two outer pentodes strapped as triodes using the 43% UL taps and lower bias voltage, while the two inner pentodes use the full OT windings and higher bias voltage.

What you are discribing is a power amplifier working in the Mixed Mode of Operation. I've thought of using such a layout for a rock amp ; having the warmness of Class A for soft tones, and the punch of Class A/B for attacks on the string. I would have liked to run a pair like Class A for a 6L6 and Class A/B for a pair of 6V6. But since I tend to run the plate volts for 6L6 much higher than what I would run for a 6V6, so I may have to give this layout some more thought. Given as such, it would probably work out to either running it with just all 4 as 6V6 or just all 4 as 6L6.

-g