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In Reply to: RE: Well hello dere 813! posted by 91derlust on October 16, 2016 at 20:19:51
If you own and run EMLs, ask Jac at Jac Music, the main man , what OP Points HE likes. He will tell you !!He will usually tell you about 10 or 11 Watts dissipation, on a Type 2A3 I THINK. Ask him.
If you run too much plate dissipation, the tube will sound thermally stressed in its music presentation, because it is thermally stressed!!
Many people who want to determine the optimum point of plate dissipation by ear, will start their explorations at the Golden Ratio, of the plate's maximum dissipation, roughly 62 percent. SO, for a 10 Watt Type 45, start at 6.2 Watts total plate dissipation. On a 250 VDC P-K differential, 25 mA. gives us 6.25 Watts.
That will be very relaxed sounding, and the tube will last for tens of thousands of hours. One can " tweak " around this point, and optimize it over time, even further, IF you are so inclined.
On a 2A3, one should NEVER run it at 250 VDC P-K and 60 mA. Golly, that is 15 Watts plate dissipation, 100 % of the tube's maximum rating. It will be stressed sounding, thermally-stressed sounding, at that point. The tube won't last long either.
However, if you have poor internal wiring, and poor out-of-time power supply energy-delivery inside the amp, " hotrodding " the op point may be necessary to your ear!! The amp may initially sound better when the op point is hotrodded, but the effect is just temporary, due to the constant thermal stress applied to the plates, in such a screwed-up conglomeration.
Build factors such as short-as-possible lead lengths, gauge and quality of internal wiring, and parts lay out, all come into play, in finding the best op point. The WHOLE amp needs to be optimized. That is why I NEVER listen to a breadboard. It isn't the real thing.
Imagine listening through crummy / long clip lead wires and clip lead terminations, versus good wire and nice Wonder Solder Signature shiny joints. All such factors, in "audio-design-by-ear", is what separates the good from the not so good.
Its NEVER easy.... to obtain high performance !!
Jeff Medwin
Edits: 10/16/16 10/16/16 10/16/16 10/16/16Follow Ups:
Ask Jack Eliano, he seems to run his tubes hot.
The practice of running tubes at the MFR. op. points dates
back to the "Golden Age" of tubes, where every drug store had
a tube tester, and every dime store had 3 of them.Underneath the tube tester(usually made by Hickok)was a stash of new
tubes. The recommended op. points were used by all MFRS-- T.V.s,
radios, Hi-Fis, Living Room consoles, etc.The WHOLE THING was TUBE SALES, and NOTHING ELSE.
Usual expected tube life was under 1000 hours-- usually about half that.
McIntosh started running tubes less "hot". Still way too hot by the
best standards today, but at least tubes weren't running away or glowing red
anymore. Those old amps aren't good performers today, but they were the
best of their time...Some still revere the old parts (they're all junk), and some still
use the old tube data-- SALES derived junk.Today we know better.
--Dennis--
Edits: 10/18/16
I would agree if it were a rare tube but design what sounds best.
You didn't explain what the amp manufacturers were getting out of it. Did they secretly own shares in the tube companies? Not sure why they would bother to be part of it other wise.
Edits: 10/18/16
The tube mfrs and stores SOLD the tubes, equipment mfrs were locked into
a kind of watts/per dollar quasi horsepower race.
The hotter they ran the tubes, the more power per dollar they got.
WATTS was what sold. "Higher-End" (there wasn't yet any real high-end except for movie theatres) was what "quality" mfrs did-- ran tubes less hot, and charged more $ per watt.
That was still too hot by today's standards, but fortunately, some good
tubes (Gold-Lion or Genalex KT-88 as an example) could take it.
Today we can easily do with 1/2 watt much more than they could do with 60 watts. Running tubes extra hot does force better transfer efficiency
and in some cases, linearity thru the tube in question, but today we can solve these problems by advanced wiring, layout, and lowered system resistances instead of cooking vacuum tubes trying to force super-conduction.
It's just common sense to find a way to do it right instead.
-Dennis--
"we can easily do with 1/2 watt much more than they could do with 60 watts."
Right.
--------------------------
Buy Chinese. Bury freedom.
"Today we can easily do with 1/2 watt much more than they could do with 60 watts."
How? wiring transfer efficiency? 3.4146 runs of some specially selected wire, arranged in parallel, serving a high output impedance source like a 12AX7's plate?
Going back to LMAO now...
cheers,
Douglas
Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.
It all comes down to the consumer in the end. Just like with transistors vs tubes. The public believed all the bull instead of doing their own comparisons and that was the start of a long slippery slope. It is still buyer beware, and the consumer's dollars can change what the manufacturers (tube or otherwise) produce. If people won't buy it, they won't produce it.
Maybe Dennis is saying that all the design engineers, back in the day, were stupid and just went along with the tube manufacturers recommendations because they didn't know any better?
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
"The WHOLE THING was TUBE SALES, and NOTHING ELSE."
Home builder misinformation, nothing else.
Just because it does not fit your 'engineering' sensibilities, or personal beliefs, does not make it so.
cheers,
Douglas
Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.
" The WHOLE THING was TUBE SALES, and NOTHING ELSE.
Usual expected tube life was under 1000 hours-- usually about half that."
That's not true. I had plenty of audio gear back in the day that saw 5,000-10,000 hours of service without a failure - guitar amps, preamps, integrated amps. Most televisions also ran their tubes at or above the manufacturers' op points and gave similar service. Lots of people can remember a TV lasting close to ten years without new tubes, probably well over 10,000 hours.
--------------------------
Buy Chinese. Bury freedom.
Can you name some of the drug store model tube testers that Hickok made?
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
I have a "u-test-m" brand drugstore type console tester as a basement decoration. It is most definitely NOT a Hickok product.
I certainly don't know everything but I am not aware of any drug store models made by Hickok.
It would be interesting if Dennis can come up with one.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
JC Morrison is or at least was a proponent of low and hot for the 845; lower voltage and higher current. At least that is what he proposed for his Dinosaur amp in SP magazine.
Edits: 10/17/16
First, determine what this sounding hot and stressed could possibly mean. Lower current idle point will run where plate resistance gets higher across half the signal. Can you hear this? Does it look like what you want? Is it what you want?
I have so far quite enjoyed running current higher, and with the idle point pushing plate dissipation ratings. With both my 6CB5A and 4E27 amps, they are idling around 90-95% of rated maximums...though going to 110% has shown no indication of trauma for the 6CB5A, even in a dark room...:)
cheers,
Douglas
Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.
"I have so far quite enjoyed running current higher, and with the idle point pushing plate dissipation ratings. "
I totally agree. It's been true for both my 211 SETs and smaller triodes like the 1626. They don't seem to wake up until the limits are approached or even exceeded. Plate curves for many tubes indicate the need to do this for best linearity. I think a great many tube aficionados simply prefer the sound of 2nd harmonic distortion.
--------------------------
Buy Chinese. Bury freedom.
"I think a great many tube aficionados simply prefer the sound of 2nd harmonic distortion."
You may be right, but I don't think I am one of them. EML tubes generally don't sound like even-order distortion and although I run them at lowish dissipation, I try to ensure linear operating points.
Maybe "stressed" = "woken-up" depending on one's sonic preferences and system context? It is quite possible to see how that could be the case.
Cheers,
91.
"Confusion of goals and perfection of means seems to characterise our age." Albert Einstein
For some reason I can't post pictures right now but a 2a3 run at 46ma, 250v into 2500 ohms (as far as i know that's how Dennis runs them) produces 4.471% THD at 1 watt.A 2a3 running at 60ma, 250v into 3800 ohms produces 2.146% THD at 1 watt.
Higher current, more plate dissipation, different load imp., less HD.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Edits: 10/18/16 10/18/16
Roughly 10% higher than the optimal load suggested by PJ's rule of thumb.
Cheers,
91.
P.S. I will be retaining a lot of these posts for future reference. Thanks.
"Confusion of goals and perfection of means seems to characterise our age." Albert Einstein
Yeah, if you're down around 45ma at 250 volts it calls for about 3.5k.
4.2k will give a little less max power but the power that it will have will be clean power.
I used to run my 300b (375v, 64ma.) into 6k. Not much power but really clean. Calls for about 4200 ohms.
Now I run at 4k (same voltage and current). More power and not as clean but still sounds good.
One can use whatever OP they want....It's just nice understanding what one is doing and what it does to the HD.
Dennis running at 46ma 250 into 2.5k is not what I would call a "good OP".
Especially when he says his amps are "the best ever......".......but I really don't what to get back into all that. :-(
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
I made a feeble attempt at SE 7B4 DC 2A3 using the reduced current biasing of finals some time ago.
That was with cheap Chinese 2A3B monoplates and ESE125 OPT's.
Tubes and OPT's seem to affect the measurements a lot.
With the quality magnetics and EML tubes DF uses, his circuit probably bench tests pretty good.
Of course, I don't ever expect to see schematics or any test results from DF about his amps.
I remember that everything about SS has to be a top secret project.
DT 667
Probably some distortion cancelling between driver and output tube.
My numbers are just the output tube.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
I doubt it from the measurements DDT posted... distortion cancellation typically results in 2nd and third distortions equalling each other because only the evens "cancel"
when you see a fft of a SE amp that doesn't have the typical dropping in distortion as harmonics go up then you have either a saturating output or driver / output even order cancellation.
dave
FWIW, Rage had a similar SE 2A3 circuit using Magnequest OPT + JJ 2A3's (not sure of the plate load or biasing) that he reported getting 1.5% THD @ 1W.
He was probably trying to copy what DF/JM did.
No matter what anyone would assert, JM will say DF is the greatest tube amp builder in the world.
The numbers I showed from the on line sim were just for comparison to each other, not for comparison to what others have done.
My numbers show that when the current is increased, increasing the plate dissipation, and the load impedance is increased from Dennis' operating point, the distortion goes down.
That flies in the face of Dennis' assertion of the idea of "thermaly stressed", what ever that means.
"...Rage had a similar SE 2A3 circuit using Magnequest OPT + JJ 2A3's (not sure of the plate load or biasing) that he reported getting 1.5% THD @ 1W."
I guess my assertion would be, if Rage was using Dennis' plate load and biasing and then increased the current and increased the load impedance his number would get even lower.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
.
Have Fun and Enjoy the Music
"Still Working the Problem"
.
Have Fun and Enjoy the Music
"Still Working the Problem"
.
Have Fun and Enjoy the Music
"Still Working the Problem"
"I think a great many tube aficionados simply prefer the sound of 2nd harmonic distortion."
And that is why I run PP, in power-limited, Class A...as I am not one of those folks.
cheers,
Douglas
Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.
Yeah, sure, build a whole friggin' finely finished amp to test out every concept you ever think of. That makes a lot of sense. To you maybe, not to me. All that is necessary is to understand that the sound will get even better when you finally do build a finished version.
Edits: 10/17/16
Thanks for repeating yourself Jeff - unlikely as it is, there maybe someone new to the board who missed it the previous gazillion times.I have asked Jac re OPs and he responded that he did not like his tubes run at low dissipation - his tubes have an ideal operating temp that would not be achieved with low dissipation points. I can't remember whether I was asking about the high gain tubes or the 2A3 - it was a while ago... but the message I got was that it applies generally to EML tubes.
Still, as a rule of thumb, I prefer points are no more than 2/3 total dissipation. I run a 2A3-S at 13W... it is less than 2/3 of the rated 28W. I have some meshies as well, rated at 17W, but don't run then in my amp often. My next build will run the 2A3s at ~42mA and 250V.
As for bread-boarding, it does allow proof of concept and reductionist experimentation that can be learned from, quickly. Not where I'd do my final tuning tho. But don't fret, I understand that reductionist inquiry is no substitute for systems approach. I reckon your builds have a particular demand for in situ voicing due to their layout.
Okay, I have dragged this even further off-topic. How about we leave it there and hope this thread can get back on track.
Cheers,
91.
"Confusion of goals and perfection of means seems to characterise our age." Albert Einstein
Edits: 10/17/16 10/17/16
ahh you guys should give Jeff a break he has a special personality type. I have another friend just like him. He has passion for our hobby too go easy..
anyways I run my little pset 1626 amplifier with double the max plate current, and IMO this is where it really sounds good. recently It has been a daily driver for when myself and my father watch Tv this amplifier was built 12 years ago.
Lawrence
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