I've been reading this thread with intense interest (and amusement) since I read the first post, and I can honestly state that I personally owned an amp with ALL of the mods listed. It was a modified Harmon-Kardon Ballad amp with the xformer impedance boogie, xtra power xformer, xtra toobz, x-cetera. It also put out xtra heat, xtra distortion... and sounded like crap, to my ears, anyway. That said, it was also not an Eico ST70, either.
If I - an absolutely retarded techno-goober of the first water without a patent to my name - can figure this all out from stuff I've read on a forum, then I can promise you these are obvious. Very, very obvious. Suggesting these mods to DIY types like us is ok, but to put them forth as some sort of new DeForest-esque epiphany is a bit of a stretch.
I do respect the original Venuzuelan builder for his ingenuity, whatever his motivation. Relatively cheap and abundant parts and supplies are par for the course here in the US; I suspect parts for building new amps are pricey and difficult to obtain in his country.
However, I'd respectfully like to know the following:
If I - an absolutely retarded techno-goober of the first water without a patent to my name - can figure this all out from stuff I've read on a forum, then I can promise you these are obvious. Very, very obvious. Suggesting these mods to DIY types like us is ok, but to put them forth as some sort of new DeForest-esque epiphany is a bit of a stretch.
I do respect the original Venuzuelan builder for his ingenuity, whatever his motivation. Relatively cheap and abundant parts and supplies are par for the course here in the US; I suspect parts for building new amps are pricey and difficult to obtain in his country.
However, I'd respectfully like to know the following:
How many dB of negative feedback constitutes "extraordinary"?
Who are the "experts" who said this couldn't be done?
Incorrect. You are confusing the novel and non-obvious tests. You need to meet both.
Just because nobody has ever put lipstick on a pig does NOT mean it's patentable.
And I absolutely DO mean any competent EE could and WOULD design these exact mods given the job of increasing the power without changing the OPT. It's not rocket science and there are only so many things you can do, all routine and obvious to a design engineer.
To Mr. Zenith
It is interesting that you claim to have built this very invention. However, to count as prior art, it must have been published or otherwise made available to the public. No banana.
As to the experts who said that the results of this project were impossible, I don't think they would appreciate being outed, especially in this pack of hyenas :-D However, you may actually be more interested in what they saw wrong with the project. The most surprising aspect to them was the fact that Andres was able to get 53W at 20Hz, undistorted, out of the modest-sized ST-70 output transformers. That was what required all the elements of the invention to come into play. I think most vacuum tube audio experts would have been surprised at that. (Of course, after seeing this, some might profess that they knew that
As for your fears of overstressing components: Hey, we're talking hotrodding here, not space engineering!
It is interesting that you claim to have built this very invention. However, to count as prior art, it must have been published or otherwise made available to the public. No banana.
---30dB was used in the ST-70A and in Andres' invention. When that was implemented in the ST-70A, we were able to make it even more stable than it was before. You can read about it here: www.tronola.com/html/st-70_mods.html
As to the experts who said that the results of this project were impossible, I don't think they would appreciate being outed, especially in this pack of hyenas :-D However, you may actually be more interested in what they saw wrong with the project. The most surprising aspect to them was the fact that Andres was able to get 53W at 20Hz, undistorted, out of the modest-sized ST-70 output transformers. That was what required all the elements of the invention to come into play. I think most vacuum tube audio experts would have been surprised at that. (Of course, after seeing this, some might profess that they knew that
As for your fears of overstressing components: Hey, we're talking hotrodding here, not space engineering!
Stew Hegeman's Citation II mods which yield similar results (double increase of output power) is a comparable technique. Additionally, it uses DC restorer to considerably drop idle current without increasing distortions, so overload of power transformer above factory imposed limits is very low. BTW, Citation II also have 30dB global NFB.
Many vintage transformers are quite big (someone call them overrated) for 3 very simple reasons - large cross-section area allowed to lower flux density and operate in the minimum distortion area below 1T - 1.2T at max power / lowest frequency (20Hz), sustain considerable imbalance of output tube idle current, and lower temperature raise (vintage transformers usually run hot because of high core loss).
The 60W transformers I designed could handle 100W without any problem for the same reason. But I don't call it overrated, but rather optimal design. Modern high-quality CRGO/GOSS steel have sow low core loss level, that even after 60W/20Hz/1 hour load (an absolutely unlikely real life scenario) temperature raise of the transformer is only 7-10 degree C.
Many vintage transformers are quite big (someone call them overrated) for 3 very simple reasons - large cross-section area allowed to lower flux density and operate in the minimum distortion area below 1T - 1.2T at max power / lowest frequency (20Hz), sustain considerable imbalance of output tube idle current, and lower temperature raise (vintage transformers usually run hot because of high core loss).
The 60W transformers I designed could handle 100W without any problem for the same reason. But I don't call it overrated, but rather optimal design. Modern high-quality CRGO/GOSS steel have sow low core loss level, that even after 60W/20Hz/1 hour load (an absolutely unlikely real life scenario) temperature raise of the transformer is only 7-10 degree C.
I think it is best to get a patent attorney to determine that.
However, regardless if an idea is patentable or not, it really boils down to the value of the IP (intellectual property).
The value here is really confined to the retrofit market and it is confined to only tube amps. Just how many modifications are there that represent the "universe" of owners looking for such an upgrade?
Then ask, how much potential money is in that market even if I harvest 100% of that market?
How long will the market last before it becomes saturated?
Then subtract the cost to patent the idea and see if it makes a business case.
My suspicion as a business owner is that the IP simply is not going to be worth that much, but I am not in the audio business, so someone else might be able to build a real case.
Nevertheless, I think there is a small niche market out there and clearly it will be a fun venture for some DIY owners out there that want to play with some old gear.
So, in my mind, the patent aspect of this is a bit academic. That's just my opinion and other people may see it differently.
To dgta:
If you fall back to using could instead of would, that is no longer sufficient to meet the teaching/suggestion/motivation test.
The point is, the only way to overturn a patent on obviousness is to prove that people were pointed directly to the invention. That is very difficult to prove and that is why obviousness is not a popular defense against patents. Look at the Amazon One-click patent, for example. Sheesh!
From page-2 of this discussion: "The classic test of obviousness is whether the prior art expresses some "teaching, suggestion or motivation" to combine the previously known elements into the invention." This means that the prior art must point to (e.g. suggest) the very combination of elements in the claim.
Look, there is a world of difference between could and would. Which is it? If you make the statement that any competent EE would [only] design with these exact mods, given that task, it is obviously false. For example they might decide to use vacuum tube rectifiers and power their heaters from the add-on transformer.
If you fall back to using could instead of would, that is no longer sufficient to meet the teaching/suggestion/motivation test.
The point is, the only way to overturn a patent on obviousness is to prove that people were pointed directly to the invention. That is very difficult to prove and that is why obviousness is not a popular defense against patents. Look at the Amazon One-click patent, for example. Sheesh!
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To woodturner-fran:
To Loren42:
--- The article was just announced two days ago.
To Loren42:
--- This was discussed earlier. That's correct, that a patent would not be expected to be worth much. The question of patentability arose because someone challenged the fact that this is a new invention and I maintain that it qualifies as an invention under US patent law.
sigh. Dancing on the heads of pins.
To summarise:
A pp valve amp can be modified by doubling the output tube compliment, halving the impedance ratio of the opt, changing the rectification to increase available current and voltage and increasing the feedback. Threse are all individually well documented techniques, and have (anecdotally) collectively been applied previously.
The purpose is to get a near-doubling of output power from the same iron.
This increase may, or may not, be at the risk of damage to said iron.
The result may, or may not, be sonically superior.
The concept may, or may not, be original.
Caveat emptor. As in all DIY, proceed with your eyes open and in full knowledge of risk and benefit.
Anything I missed?
To summarise:
A pp valve amp can be modified by doubling the output tube compliment, halving the impedance ratio of the opt, changing the rectification to increase available current and voltage and increasing the feedback. Threse are all individually well documented techniques, and have (anecdotally) collectively been applied previously.
The purpose is to get a near-doubling of output power from the same iron.
This increase may, or may not, be at the risk of damage to said iron.
The result may, or may not, be sonically superior.
The concept may, or may not, be original.
Caveat emptor. As in all DIY, proceed with your eyes open and in full knowledge of risk and benefit.
Anything I missed?
This is what we call a risk.
If I did this in a design I'd have my line manager breathing down my neck wanting to know what the hell I was doing.
When all is said and done, you are much more impressed by these tweaks than we are. This is not uncommon when somebody with comparatively little experience in a field presents what he thinks is a radical approach to people with a lot of experience in that field. You can argue 'til you're blue in the face about patents, all you're going to catch with this is people with as little experience as yourself. You're only the monkey anyway, you're not the organ grinder. Catch yourself on.
I'd be less concerned with damage than LF distortion. Eico used transformers with pretty large cores for most of their amps, so in this particular application of well-known techniques, you can get away with it. Their tradeoff was higher leakage inductance and poorer side-to-side balance than more expensive iron. With other transformers, the LF distortion will get pretty ugly.
I could have none, you'd still be a novice in the face of the assembled experience here.
I did you the courtesy of being blunt. If you find the information unpalatable, sobeit.
Please explain how the GNFB qualifies as extraordinary.
My take on both your site and the reference site is that you have increased GNFB by 3-6dB. The proposal to use a 10K pot in the feedback comes with notes that too much feedback can lead to instability. This was common knowledge in the tube era and is discussed in RDH4, Crowhurst.etc.
So I don't see how it qualifies as anything out of the ordinary. I've seen more than one old design with 30dB or more GNFB.
40, 50 or 60dB of feedback might be Extraordinary.
My take on both your site and the reference site is that you have increased GNFB by 3-6dB. The proposal to use a 10K pot in the feedback comes with notes that too much feedback can lead to instability. This was common knowledge in the tube era and is discussed in RDH4, Crowhurst.etc.
So I don't see how it qualifies as anything out of the ordinary. I've seen more than one old design with 30dB or more GNFB.
40, 50 or 60dB of feedback might be Extraordinary.
I couldn't have stated my case better. This was not an invention. These were simply ideas I gleaned from this very forum. I didn't "publish" this "invention" because I discovered nothing and my efforts yielded a terrible-sounding result (subjective, of course). If you or anyone else were able to achieve listenable results with another amp, then I heartily congratulate you. Good luck in your quest.
No orange.
Why not? This forum - while full of "amateurs" - isn't exactly the electronic equivalent of The Jerry Springer Show. Any expert in the area of tube audio should be more than willing to stand on his or her facts right here. I'm sure that as a holder of an MSEE degree you'll know what I mean. I asked only in the spirit of open-mindedness; I'm more than willing to listen to anyone with a different view from my own, as long as it's in a forum where fact-based discussion in an atmosphere of mutual respect is the rule of the day.
No apple.
I am deeply grateful to many members of this "pack of hyenas"; they have never failed to give me sound advice when I needed it most. Some of my inquiries to members of this "pack" must have bordered on imbecilic, yet the answers I have received were always thoughtful and sometimes humorous. Sometimes the advice I received wasn't what I wanted to hear, but I rest assured knowing it was never given in a mean-spirited manner. Taken as a group they have taught me how to experiment courageously, economically and above all, safely - and for that I am most grateful. As a junior member - very, very junior member - of the pack, I am more than willing to gnaw on the bones of the carcasses that my more senior pack mates have left behind.
Sour grapes.
To Tubelab:
Should there ever be a "Tubelab Trademark Registration Fund", I hereby let it be known that I'll do my d***dest to make sure that the first $20 will come from me.
I think I'll get off now lest I surely incur the wrath o' the moderator...
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