A clone of the Lazy J J20?

[Pedro Vecino]

My doubt comes from when I measure the intensity on the plates (in cathode biased push-pull amps like a Deluxe 5E3 or an AC30). When playing with them in a wide volume range, the intensity remains unchanged and when I exceed a certain volume threshold the intensity decreases.
Now I wonder if I dreamed it...

[Helmholtz]

My doubt comes from when I measure the intensity on the plates (in cathode biased push-pull amps like a Deluxe 5E3 or an AC30). When playing with them in a wide volume range, the intensity remains unchanged and when I exceed a certain volume threshold the intensity decreases.
Now I wonder if I dreamed it...

What do you mean with "intensity"?

[Chuck H]

Please show me at least one schematic.

Well don't put me to it like that I probably should have said "many purportedly push pull class A guitar amps". With that caveat I don't have a schematic to show you. I CAN say there are many push pull cathode biased amps that idle the tube at or very near 100% dissipation. Among these would be the VOX AC30 and even the Fender 5e3 for some units. I think this is where the class A fallacy comes from.

[Chuck H]

My doubt comes from when I measure the intensity on the plates (in cathode biased push-pull amps like a Deluxe 5E3 or an AC30). When playing with them in a wide volume range, the intensity remains unchanged and when I exceed a certain volume threshold the intensity decreases.
Now I wonder if I dreamed it...

Especially true in tube guitar amp design is see saw effect of current and voltage. Your pervieved compression is absolutely real. But as current increases voltages decrease. "Intensity" in this case would be the center of the see saw.

[tzurby]

n this case I'll guess that no one is referring to the "iron" itself but rather using the word iron to indicate the whole transformer.

Wow, these are very valuable information. (The quote I use is just an example - and shows that I, probably like most guitarists, have no idea about electronics in general and tube technology in particular. - But want a good tone... Without spending thousands of $... I could just buy a J20, but €3000+ is just too much for me.)

I will go with these information to my tube amp tech. I am sure, he understands all this.

May I ask were to find your "most popular amp design"?

[Chuck H]

May I ask were to find your "most popular amp design"?

Haha !

I'm an amateur overall. I only made six of them and never earned a penny But I will brag that it sounded good enough to get me a gig with Dean Markley at the 2009 Winter NAMM show. Dean still has one, I have one and it's the only amp I use. Dean sold his company and went into retirement soon after that so the design never made it into production. That would be two of the six. The others are in the hands of players that heard it and wanted one. I haven't built one in twelve years.

[Pedro Vecino]

What do you mean with "intensity"?

Especially true in tube guitar amp design is see saw effect of current and voltage. Your pervieved compression is absolutely real. But as current increases voltages decrease. "Intensity" in this case would be the center of the see saw.

Sorry, I meant to say current. In Spanish when we say intensity it´s always referring to the current.
For example: I have a Deluxe 5E3 with 360 volts on the plates and two ammeters connected across the plate connections. I get 36mA through each of them with no signal at the input. That current remains constant playing at low and moderate volumes, but when I cross a certain threshold (already developing high volume) that current decays. Around 34, 30mA or less. The moment I stop playing it returns to the initial 36mA.
Like I say, I hope I didn't dream it. I'll check back when I have the chance.

[g1]

(We are talking about the tone gets compressed and then blossoms again, right? Like in Neil Young, famously here: https://www.youtube.com/watch?v=eNQnXS9—oM) It is about the sweetness of the tone in general, about harmonic content, a rich as opposed to a sterile tone.

For some reason the link is not working. Because I'm such a big fan I will embed the clip here, and also boast that I was fortunate enough to see him on this tour in '91 (with Sonic Youth and Social Distortion).

[Helmholtz]

Sorry, I meant to say current. In Spanish when we say intensity it´s always referring to the current.
For example: I have a Deluxe 5E3 with 360 volts on the plates and two ammeters connected across the plate connections. I get 36mA through each of them with no signal at the input. That current remains constant playing at low and moderate volumes, but when I cross a certain threshold (already developing high volume) that current decays. Around 34, 30mA or less. The moment I stop playing it returns to the initial 36mA.
Like I say, I hope I didn't dream it. I'll check back when I have the chance.

[#8203;

Plate current with signal is a mixture of AC and DC. Not all meters can cope with that.
Best monitor cathode voltage, which is proportional to total current.
The bypass cap makes sure it's pure DCV.
As soon as cathode voltage increases by more than maybe 5% (taking care of increased screen current), the amp leaves class A.

[Helmholtz]

I CAN say there are many push pull cathode biased amps that idle the tube at or very near 100% dissipation. Among these would be the VOX AC30 and even the Fender 5e3 for some units.

Yes, but 100% plate dissipation (or even more) doesn't ensure class A operation.
An AC30 would run in class A if B+ was only 230V. But then output would be only 20W.
Guitar amp designers typically go for max.output power with a given set of power tubes.
So they increase B+ as much as tolerable, thus leaving class A.

Best indicator is cathode voltage.
Or just feed your circuit data to this calculator:https://www.vtadiy.com/loadline-calc...ge-calculator/
Transition from class A to class B shows as kink in the loadline.

I actually think that pure class A with a PP guitar amp is not really desirable,.

[Helmholtz]

When I see the term "transformer iron" I think of core size and material.
Core material actually is specially processed silicon-steel. There are several grades differing in power loss per unit volume (so are more efficient), permeability and saturation limit.

[g1]

When I see the term "transformer iron" I think of core size and material.

This is true. But the word 'iron' is used by itself as slang for 'transformer' when in a tube amp context. I get the impression that the original quote used it in this slang manner.

[Chuck H]

And the verbatim of the phrase in question wasn't "transformer iron". It was "less efficient iron" in reference to the PT. In context it doesn't seem to imply less efficient laminate material. I do believe the phrase "less efficient iron" in the quoted post was intended to simply mean "less efficient transformer".

[Helmholtz]

It was "less efficient iron" in reference to the PT. In context it doesn't seem to imply less efficient laminate material. I do believe the phrase "less efficient iron" in the quoted post was intended to simply mean "less efficient transformer".

I understand he tried a PT using higher grade laminations and didn't like the sound.
(In fact less sag means higher efficiency.)

[loudthud]

So far, nobody has mentioned the filter capacitors. The difference between 16uF and 22uF is often dismissed, but I think there is a slight difference. IIRC the original 5E3's had caps rated at 475V because the B+ went that high before the 6V6s warmed up.

The thread linked below had some pics showing the class AB nature of a 5E3, but links to the pics are broken. I'll have to search for backup copies.

Link: https://music-electronics-forum.com/...29684-b-ripple