I don't dispute your findings. I have no experience with the Eico ST-70, so I cant express an opinion here.
I do state that I have experimented with a lot of OPT's over the years. I have experimented a lot with the Schumakers since I bought a lot of them.
I can say that in a vacuum tube audio amplifier OPT saturation can manifest itself in several ways, all of which are quite audible. In some cases the OPT's inductance collapses causing an abrupt increase in tube current which causes the OPT to saturate further. This can occur rather quickly and the tube current can double in a millisecond or two.
I have studied this effect quite a bit while learning to stretch an 18 WPC amp to 125 WPC. Granted, I was using sweep tubes which have a peak cathode current of 1.1 AMPS. This large peak current capability along with some local feedback and is my preferred method of squeezing more power through an OPT. Running the OPT at 3300 ohms and applying a secondary power transformer to boost heater current to 10 amps and B+ voltage to 600 volts are the methods used to get the 125 WPC.
The delay effect of a saturating OPT was captured with a scope probe measuring OPT secondary voltage and a second probe measuring output tube cathode current.
So if you were considering new and novel ways to combine 4 different common elements in a unique way look into the red board thread (link in an earlier post).
There IS a 6600 ohm OPT ratioed down to 3300 ohms in my build. Other builders purchased a 3300 ohm OPT.
There IS a bargain power trasnformer in several builders amps with an additional power transformer to boost the B+ from 340 volts to 600 volts and provide the additional heater power to support the larger tubes used.
There IS one build (mine) where 4 output tubes were used to extract 525 watts from a single board using a bench power supply cranking 650 volts at 1.4 amps into the board.
All builds used Schade type feedback which has been known since the invention of the 6L6 in the late 1930's to reduce the output impedance of the pentode output stage.
Just another 4 part invention........
It seems to me there's really only one idea here, and it's a rather standard one; add paralleled output tubes to increase the output power. This brings some concomitant issues that need to be fixed: (1) The OPT is getting driven beyond spec, producing large distortion, so increase the feedback; (2) The filament supply can't cope with the extra load, so add an extra one; (3) The HT supply isn't up to it, so replace the rectifier with an SS one.
If it had turned out that the extra power consumption had been a bit more then you would have needed in addition: (4) Replace the power cord with a heavier gauge one and (5) Increase the rating of the fuse. The you could have said that all six modifications were needed, and had never been done simultaneously before. Big deal.
The fact that you can apparently achieve a reasonable performance at the increased power levels is of some interest, but the claims of originality about the methods for achieving it seem to be exaggerated. The point of interest is getting lost among the overblown claims, I think.
Chris
If it had turned out that the extra power consumption had been a bit more then you would have needed in addition: (4) Replace the power cord with a heavier gauge one and (5) Increase the rating of the fuse. The you could have said that all six modifications were needed, and had never been done simultaneously before. Big deal.
The fact that you can apparently achieve a reasonable performance at the increased power levels is of some interest, but the claims of originality about the methods for achieving it seem to be exaggerated. The point of interest is getting lost among the overblown claims, I think.
Chris
Ah--So, there we have it....
Bench tests in the lab suggest the OPT of ST70 will pass 79W at 20Hz with reasonable fidelity....
(Regardless the steepness of the saturation slope or hysterisis)
So, THATS the reason the extra power is fully available--The Quality of the original ST70 transformers, NOT the alleged modification adding extra tubes and hurds of feedback!..
Proper, ST70 Transformers are actually quite a work of art, the winding configuration is really complicated....
Bench tests in the lab suggest the OPT of ST70 will pass 79W at 20Hz with reasonable fidelity....
(Regardless the steepness of the saturation slope or hysterisis)
So, THATS the reason the extra power is fully available--The Quality of the original ST70 transformers, NOT the alleged modification adding extra tubes and hurds of feedback!..
Proper, ST70 Transformers are actually quite a work of art, the winding configuration is really complicated....
To Tubelab.com: You do mention some interesting goodies, we should keep in touch.
To cnpope: Sorry you arrived so late to the party. That level is long buried. Read the thread, if you're interested. You missed the half-impedance transformer operation and the fact that the NFB is extraordinary. (No we're not going to start that again!--sorry in-thread-joke
To Alastair: No, it's all of the above, and not one element can be left out! Read the thread or <gasp> article if you're curious why.
To Tony: A 5th? Yes! But only if it greatly increases the output, like the others.
Well, I must say that it's been real special hanging out with you hyenas but I gotta get back to all the other projects--you know how it is. Not that I'm really going away--you can always reach me through the website. And you can even comment on the article, in the reader comments, right there with it.
Hope you had fun with all this. I did too.... kinda
Cheers, Steve L.
PS: Don't bail on the party, on my account! I'm sure you hyenas will find some other meat to feed on! Har! Sorry, couldn't resist. Take care.
To cnpope: Sorry you arrived so late to the party. That level is long buried. Read the thread, if you're interested. You missed the half-impedance transformer operation and the fact that the NFB is extraordinary. (No we're not going to start that again!--sorry in-thread-joke
To Alastair: No, it's all of the above, and not one element can be left out! Read the thread or <gasp> article if you're curious why.
To Tony: A 5th? Yes! But only if it greatly increases the output, like the others.
Well, I must say that it's been real special hanging out with you hyenas but I gotta get back to all the other projects--you know how it is. Not that I'm really going away--you can always reach me through the website. And you can even comment on the article, in the reader comments, right there with it.
Hope you had fun with all this. I did too.... kinda
Cheers, Steve L.
PS: Don't bail on the party, on my account! I'm sure you hyenas will find some other meat to feed on! Har! Sorry, couldn't resist. Take care.
I have built a lot of amplifiers in the past 45 years both tube and solid state. The biggest one was a single channel solid state monster that put out 1200 watts using 24 X 2N3773 transistors. I built that one back in 1971 when 1200 watts was an unheard of amount of power. It was used by a rock band for a PA system. It destroyed a lot of speakers in its day. I last saw in in the 80's when I replaced its electrolytic caps. It could still be out there somewhere.
I will still build a big stereo tube amp in the not too distant future just because I bought a pair of Plitron toroidal OPT's that are rated for 400 watts @ 20 Hz. Incidently these OPT's are 1250 ohm CT into 2, 4, or 8 ohms. I have used them ratioed UP as 2500 ohm and 5000 ohm OPT's, so you can go the other way too. Plitron OPT's are so good that you dont see much change in performance doing this. As with most toroids good DC balance is needed for best results.
I must admit that the best sounding amp I have ever built makes all of 2 WPC, and the amp I use most does about 8 WPC in triode or 14 WPC in UL. The 125 WPC red board feeding 96db speakers with 15 inch woofers IS the go to system when you want a rock concert in your living room.
Seems to me that Alastair hit the proverbial nail on the head. The OPTs are able to handle more power than the original circuit ran. Everything else after you put double the output tubes is merely making it work.
The issue of adding extra feedback is all well and good, but I would put this thought out there - I believe the OP's site does show some square wave results - which are not too awful at all. Actually pretty decent compared to a typical stock amp of this ilk, but they're more ringy and likely not as clean as a ZFB version of much the same output tubes and OPT... I' d speculate.
So, it looks like a nice job of doing heavy NFB... of course that all depends on how it actually sounds. ... claims nothwitstanding.
_-_-bear
The issue of adding extra feedback is all well and good, but I would put this thought out there - I believe the OP's site does show some square wave results - which are not too awful at all. Actually pretty decent compared to a typical stock amp of this ilk, but they're more ringy and likely not as clean as a ZFB version of much the same output tubes and OPT... I' d speculate.
So, it looks like a nice job of doing heavy NFB... of course that all depends on how it actually sounds.
... claims nothwitstanding. _-_-bear
Having trouble taking this thread seriously - well ther was a small amount of useful technical stuff buried herein.
Sorry to poke fun at all you "Yanks" but the US Patent Office is a serious joke. You can patent just about anything as long as you "pays your money".
Just one example, have a look a the many patents of Randall Smith (Mesa Boogie) for guitar amps stuff.
He holds the patents on stuff straight out of Radiotron Designers Handbook. In fact not one of his patents would pass any sort of rigorous scrutiny.
This is so bad that many folk choose not to patent, why? To protect their Intellectual Property. The Patent Office is so incompetent that we avoid them to protect what they were established to protect.
Tongue firmly in cheek:
I believe the US is looking for some budget cuts, well you start with ditching the Patent Office.
Cheers,
Ian from "Down Under"
(we'll poke fun at anyone, we are not the slightest bit prejudiced).
Sorry to poke fun at all you "Yanks" but the US Patent Office is a serious joke. You can patent just about anything as long as you "pays your money".
Just one example, have a look a the many patents of Randall Smith (Mesa Boogie) for guitar amps stuff.
He holds the patents on stuff straight out of Radiotron Designers Handbook. In fact not one of his patents would pass any sort of rigorous scrutiny.
This is so bad that many folk choose not to patent, why? To protect their Intellectual Property. The Patent Office is so incompetent that we avoid them to protect what they were established to protect.
Tongue firmly in cheek:
I believe the US is looking for some budget cuts, well you start with ditching the Patent Office.
Cheers,
Ian from "Down Under"
(we'll poke fun at anyone, we are not the slightest bit prejudiced).
My particular "best amp" in a Tubelab SSE with 45's.
I make and sell boards for a push pull amp that uses EL84's or 6CW5's. Some builders have called them their "best amps". I have two and they are similar sounding good amps but not my best. They both use the ultra cheap Schumaker OPT's that I have discussed previously in this thread. The EL84 amp runs at 325 volts and the OPT's are used as designed at 6600 ohms. Power output is about 18 watts from 25 Hz to 15 KHz. The 6CW5 amp runs at 245 volts and the OPT's are ratioed down to 3300 ohms. Power output and sound quality is similar. The 6CW5 and the EL84 are similar tubes with the screen grid construction being the only difference. In this case the ratioing down of the OPT did not make much difference in the audible or measured performance of the OPT. I will eventually try these amps with a good set of OPT's.
These are the same OPT's that I ran in my 300Beast 30 watt push pull amp at 6600 ohms, and in the red board at 125 WPC using 3300 ohms. In this case the lowered drive impedance of the zero feedback 300B or the Schaded 6HJ5 can push this transformer around and force some good sound through it. The red baord will make about 80 watts at 30 Hz.
We all know that the patent system is broken. A few of the patents that I hold are rather lame and useless. One of my friends actually got a patent for a pager that shocks the user on command. These things have been used for electric dog fences for years, but strap one on a human and it gets granted a patent.
The patent system isn't the only thing thats broken in Washington, but we don't discuss that on this forum.
is very strange that someone here(in this thread) has not said that I build a tube amp of 1000000W at 7 years of age but that was not saying at this moment. I built my first tube amp with PP 6BQ5 when I was 16 years old, I also built a solid state amp with a 2N3055(140Wrms) in quasi-complementary configuration to 18 years old and 32 years later still works, HOWEVER do not consider myself a expert (humbly believe that I am very far from it). my dad (in peace REST), surely would have been able to build a tube amp with your eyes closed, but never (like me) was "close" to listen to the ideas of others, I think that is the true "essence" of an expert
if still alive "Nikola Tesla" probably would have felt intimidated to publish something not to be attacked by many "experts"
I apologize if I offended anyone.....
if still alive "Nikola Tesla" probably would have felt intimidated to publish something not to be attacked by many "experts"
I apologize if I offended anyone.....
Building a tube amp with your eyes closed might just be possible (look out for soldering iron burns, though) but I would not recommend testing/debugging with eyes closed. Difficult to see the scope traces, and risk of electrocution.
You might not realise that some people on here (not me) are not "experts" but genuine experts. A genuine expert will always listen to others, but then they might not like what he says in response. Some of what Tesla said (in his later years?) was barmy.
Not offended, just amused.
You might not realise that some people on here (not me) are not "experts" but genuine experts. A genuine expert will always listen to others, but then they might not like what he says in response. Some of what Tesla said (in his later years?) was barmy.
Not offended, just amused.
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