I think the whole thing is mostly a new way to market "class A" but not say it cause everyone's marketing team has made class A 20-years-ago's buzz word.
that would make some sense, as far as marketing goes, the "class A" term went from being the greatest thing ever, to some people realizing that class of operation doesn't really matter as long as you like how the amp reacts and sounds.
> go about measuring the current on the el34s of the alessandro?
"The voltage at cathode pin before the cathode resistor/cap is 12V. The cathode resistor value is 82ohms"
12V across 82 ohms is 0.143 Amps or 143mA.
This appears to be per-pair? Then roughly 71mA per tube.
> I know for a fact that the alessandro runs in class A
How do you know that?
> the dissipation ought to be 100%, right?
To get the most out of your tube-dollar, yes.
Tube-dollar may not be the most important thing. You sure can run tubes far below their ratings.
> The plates on those EL34s measure 228Volts
Minus 12V at cathode, 216V plate-cathode.
Times 71mA per cathode, 15 watts per tube. Assuming G2 current 15% of plate current, then 13 Watts per plate. Half of original rating on EL34.
> runs HOT, really HOT
Chassis is mighty small for 4*0.071mA*228V= 65 Watts of total heat.
That looks like the calculations I made were correct.
As far as the chassis being too small, I though so too, but then I tried running the amp with the chassis out of the cab so it had plenty of ventilation, and it was still quite hot, obviously the fact that the quartet of EL34s is really close together physically might not help.
I assume I know it's operating class to be A, because George claims his amps are designed to work in class A at full unclipped output of the amplifier. I'm no good with looking at load lines to check if this is true or not, but the transformers are specially made by magnequest for an amp that runs at really low plate voltage and high current.
It must also be noted that his amps use ultralinear taps, going to the grids of the tubes with 1k resistors for a total of 233v at the grids.
What do you think, could it be considered to be operating in class A? George rates this amp at 20 Watts. It sure doesn't feel like a 60 watts amp, more like a 15-25 watts one.
I don't think I recall 65 amps claiming their tubes run cool. I do recall them saying your tubes would last 20 years. I'd like to know how they arrived at that number.
The cathode of a tube won't last forever, and there's many things that can cause a tube to have reached the end of its useful life that have little to do with how its used. However, abuse typically hastens end-of-life.
I got the impression that they designed the amp to be within modern production tubes' ratings, and not necessarily designed for maximum power output (like when he said 2x EL34 amps were too loud). I wouldn't sweat the details of a brief demo aimed at selling you a 65 amp.
Besides, the only potential selling point was being able to switch between different distortion sounds and clean sounds at a single volume level. It sorta did that, but the distortion sounds weren't "wow" to me. And I didn't feel the clean sound (based on what was captured by probably the interviewer's mic) was any better than what you could get out of an early-70's Marshall.
I saw a webcast by Dan Boul, where he claimed no one else in the market to be using tubes this way (which I think is not really accurate), where he also claimed typical EL34 amps don't sound that good clean (which I also think is incorrect) and finally where he said their new producer amp, ran so cool you could pickup the tubes by hand after hours of play and while they might still be warm, you wouldn't even get burnt.
You could install a VVR in an amp in a fixed position setting a low voltage on the power tubes.
with respect, Tubenit
I've taken that into consideration too, might be a nice option.
I'd also like to add that, despite the fact that part of the topology of the alessandro is pure fender, the amp sounds and responds very differently from a 60s fender, it sounds really really great with it's own voice going on and never harsh with great top end extension, plenty of chime and lots of definition. Despite all the filtering it doesn't respond in a stiff way and it's very linear, everything responds very smoothly, more so than any other amp I've tried. The transition from clean sounds to distorted ones, is non existant, it just blends into saturation in a marvelous way.
Topic: Question regarding low plate voltage and high current (with measurements) (Read 4517 times)