Killing crossover distortion

[Stevem]

In terms of getting this done would you folks go with the Paul Ruby method ( see Paul Ruby / killing the buzz) of placing a Two diodes ( a Zener and a non Zener) on each OT grid input , or the Fender Bassman AB165 version of placing a 220k resistor from each outputs plate back to each PI plates output?

The Ruby version does not kill off the output power and still seems to leave some overshoot in place, the Fender way is pure square wave with some duty cycle shift like the Ruby fix, but knocks off about 6 watts of power.

[pdf64]

the Fender way ... knocks off about 6 watts of power.

Is that using the correct circuit driving it?
I seem to remember a thread where a 12AX7 was being used in place of the 12AT7 for the LTP with one of these, and power was being reduced.
But that may have been due to the 12AX7 having excessive plate impedance.

My preferred method to reduce bias shift under overdrive is to reduce the value of the power tube control grid leak resistors, eg from 220k to 100k, as this one change has multiple benefits, mitigating issues with minimal effect on the good stuff.

[martin manning]

What circuit are you working with Steve?

[Leo_Gnardo]

Killing crossover distortion, at what output condition? Certainly if there's sufficient bias current, there will be no crossover distortion until you reach clipping. By the time you're clipping, there's audible distortion & what does it matter whether it's clipping or crossover. For those who want a little extra margin, you can dial the bias a little hotter then crossover distortion won't show up until the amp is deeper into clipping. Comes a point you get the buzzsaw effect, who cares clip or crossover.

Never did much like the 220K plate to grid feedback R Fender design. Zener clipping at PI input, sure you can pick a value that will fuzzbox your audio before any dreaded crossover distortion shows up but now you've subsfituted an even more obvious-to-the-ear distortion.

I don't see what's the point but then again I'm only half way thru my first cuppa coffee & it's upsetting enough to hear one of my heroes, the world's foremost tautologist Yogi Berra has left the field permanently. I bet he'd have something to say about this.

[Stevem]

The buzz saw part of the distortion is what I am playing around with as those harmonics are very offensive to my ears in other amps!
This AB165 a Bassman circuit knocks off about 6 watts of peak output when it's in place ( 220k) from what I have seen, it's no big deal, I am just making note of it.
Last night I upped the 220k resistors to 330k and saw little change, still fat square waves at clipping with no over shoot.

Yes, that was my post on swapping out the at7 PI in this amp with a ax7, but my notes I was taking are missing at the moment.

[rp]

...the world's foremost tautologist Yogi Berra...

Yogi also practiced medicine?!

Berra’s Yogi-ness was exploited in advertisements … perhaps most famously Yoo-Hoo chocolate drink. Asked if Yoo-Hoo was hyphenated, he is said to have replied, “No, ma’am, it isn’t even carbonated.”

[Leo_Gnardo]

...the world's foremost tautologist Yogi Berra...

Yogi also practiced medicine?!

Berra’s Yogi-ness was exploited in advertisements … perhaps most famously Yoo-Hoo chocolate drink. Asked if Yoo-Hoo was hyphenated, he is said to have replied, “No, ma’am, it isn’t even carbonated.”

If you need a laugh, tautology is good medicine. In some of his TV ad gigs Yogi had script writers to do it for him. AFLAC insurance ad: "They give ya cash, which is just as good as money."

I always loved "That place is too crowded, nobody goes there anymore."

And made up a few of my own, never as good.

When I was a very young pup @1960 my Mom would sometimes drive me past Yogi's house in Montclair and point it out, nice big place with post-and-beam appearance, sort of Olde English look. Couple years later my Dad was hired to build a tract housing development across the street from chez Yogi. They got acquainted but this wasn't made known to me until after Dad passed away 1989. It's all history now.

And none of it has anything to do with eliminating crossover distortion. Please excuse the hijack folks, back to the business at hand, if there is any.

[Teleguy61]

When you come to a fork in the road, take it.

[Stevem]

It's getting late earler !
On talking about eating a Pizza he said, " Don't cut it in 6 slices I can't eat the whole thing, make it four!"

[Leo_Gnardo]

You can observe a lot, by watching.

[Structo]

Hehehehehe