HOT OR BOILED WATER
Regards to all!
Well, this new thread seems to attract much more attention than a thread on EL84 amps can do! Great... only it takes much more time and attention when replying -- unless one wants to be targeted!
As Choky put it, it's all boiled water, maybe boiled a long time ago, evaporated... and now it's back again as rain.
I have already seen previously to this post Gary P.'s nice amp with direct heated pentodes (the globe ones
). Oh, how I sometimes envy people how live elsewhere where they can find all these goodies... and do not tell me you bought them on E-bay or something, since it had to arrive to you by post, which in the case of where I live is not as easy (there are Trolls in the post office who like stealing nice stuff).
Gary's schematic is "different" in the fact that it actually does not have Ra above the driver tube + is DC coupled (a la alternative version of Loftin-White). Well, his "copyright" states 2004. -- while I did the first RH2G schematics in 2002. (what I now call the RH88 instead of RH6550, due to popular demand for the name). On the other hand, JB maybe wrote the article even before... and if anyone believes, I was thinking about making the RH2G both without Ra (only Rfb) and direct coupled... the world is a small place, and disputing who did it first takes people nowhere!
This is, incidentally, another issue I wanted to discuss about -- although I personally do not play with PP amps, the principle is fully applicable to PP amps. Furthermore, if one wants to put it that way, a PP amps can be "simplified" as two symmetric SE amps with a phase splitter and "common transformer" (if I am at liberty to call it that way). Gary's schematic actually shows how that can be done. Applause!
Now for another "boiled water" issue: 1624 and 1625 are all members of the 6L6 family, just like 807 (which is almost identical to 1625, if I did not get the datasheets -- mil.spec. -- wrong). Well, for that matter, the RH807, previously mentioned, was already built in several different versions, including one with 1624 -- if I am not confusing it, it looks the same as 807 but is DH and fits the same socket? Well, I think that for that case I had to redo somewhat the circuit (higher value Rk of output tube) not to surpass anode dissipation ratings... Well, boiled water, a long time ago...
If someone wonders, any SE amp -- and RH amps too, of course -- can be built as para-feed: and, parafeed versions of the RH807 were built already, both with 807s and 6L6s!
What cannot be done...
If we are talking about the "RH mode" I think that it does not fully hold true... the feedback is effective, since the feedback path still exists -- but it does not work "the same way", just like the difference between RH and T-Rex, if I am at liberty to compare with such very well known and established figures...
Another mention about the 2A3 amp with feedback between plates of the driver and output tube: feasible, of course... and improves the sound. The improvements are on a completely different plain from that which some are now trying to stir us onto. BUT, and the but is big *!* it is necessary to redo the operating points etc. and to carefully choose the "sweet spot" where things get really going.
Finally, while the thread is now attracting more attention, I am afraid that not all the attention will be nice... (too many people grinding their axes right now...) that is why I already said "if I'm at liberty to say" far too many times. Well, if it gets verbal and "boring"... I am not 7 feet tall. But I can always turn my back -- whoever wants can always contact me by mail
Regards to all!
Well, this new thread seems to attract much more attention than a thread on EL84 amps can do! Great... only it takes much more time and attention when replying -- unless one wants to be targeted!
As Choky put it, it's all boiled water, maybe boiled a long time ago, evaporated... and now it's back again as rain.
I have already seen previously to this post Gary P.'s nice amp with direct heated pentodes (the globe ones
). Oh, how I sometimes envy people how live elsewhere where they can find all these goodies... and do not tell me you bought them on E-bay or something, since it had to arrive to you by post, which in the case of where I live is not as easy (there are Trolls in the post office who like stealing nice stuff).Gary's schematic is "different" in the fact that it actually does not have Ra above the driver tube + is DC coupled (a la alternative version of Loftin-White). Well, his "copyright" states 2004. -- while I did the first RH2G schematics in 2002. (what I now call the RH88 instead of RH6550, due to popular demand for the name). On the other hand, JB maybe wrote the article even before... and if anyone believes, I was thinking about making the RH2G both without Ra (only Rfb) and direct coupled... the world is a small place, and disputing who did it first takes people nowhere!
This is, incidentally, another issue I wanted to discuss about -- although I personally do not play with PP amps, the principle is fully applicable to PP amps. Furthermore, if one wants to put it that way, a PP amps can be "simplified" as two symmetric SE amps with a phase splitter and "common transformer" (if I am at liberty to call it that way). Gary's schematic actually shows how that can be done. Applause!
Now for another "boiled water" issue: 1624 and 1625 are all members of the 6L6 family, just like 807 (which is almost identical to 1625, if I did not get the datasheets -- mil.spec. -- wrong). Well, for that matter, the RH807, previously mentioned, was already built in several different versions, including one with 1624 -- if I am not confusing it, it looks the same as 807 but is DH and fits the same socket? Well, I think that for that case I had to redo somewhat the circuit (higher value Rk of output tube) not to surpass anode dissipation ratings... Well, boiled water, a long time ago...
If someone wonders, any SE amp -- and RH amps too, of course -- can be built as para-feed: and, parafeed versions of the RH807 were built already, both with 807s and 6L6s!
What cannot be done...
If we are talking about the "RH mode" I think that it does not fully hold true... the feedback is effective, since the feedback path still exists -- but it does not work "the same way", just like the difference between RH and T-Rex, if I am at liberty to compare with such very well known and established figures...
Another mention about the 2A3 amp with feedback between plates of the driver and output tube: feasible, of course... and improves the sound. The improvements are on a completely different plain from that which some are now trying to stir us onto. BUT, and the but is big *!* it is necessary to redo the operating points etc. and to carefully choose the "sweet spot" where things get really going.
Finally, while the thread is now attracting more attention, I am afraid that not all the attention will be nice... (too many people grinding their axes right now...) that is why I already said "if I'm at liberty to say" far too many times. Well, if it gets verbal and "boring"... I am not 7 feet tall. But I can always turn my back -- whoever wants can always contact me by mail
SY and EC,
It doesn't matter what it's called! It is undoubtedly boring old local feedback, but seems to have accumulated some interesting names over the years... no doubt in an attempt to make it more interesting. And yes, EC, you missed the point
Gary,
I have followed your development of the 47 PP amp with great interest. In fact I'm working on a variation on the theme right now with KT33 outputs and 6BX6 input/drivers/phase splitters.
Alex,
Please do not be offended by this post, I most certainly have not been "grinding my axe"!
Gary's original PP 47 'Inverse Feedback Pair Amplifier' (I like that name ) schematic is dated the 9th March 03, which still means that your RH84 predates it. The John Broskie article was published in March 2001, so I'm not sure if the RH84 predates that since the RH84 schematic is dated '2001'. Nonetheless, the Radiotron Designers' Handbook (4th edition), in which this topology is described, predates both designs by almost fifty years. It apparently was also somewhat popular in the AF output stage of vintage radios. It may very well have been an original idea to you, but whoever thought of it first, or built the first amp based on it does not matter, and in any case is most unlikely to have been you, Gary Pimm, or for that matter, John Broskie.
It doesn't matter what it's called! It is undoubtedly boring old local feedback, but seems to have accumulated some interesting names over the years... no doubt in an attempt to make it more interesting. And yes, EC, you missed the point
Gary,
I have followed your development of the 47 PP amp with great interest. In fact I'm working on a variation on the theme right now with KT33 outputs and 6BX6 input/drivers/phase splitters.
Alex,
Please do not be offended by this post, I most certainly have not been "grinding my axe"!
Gary's original PP 47 'Inverse Feedback Pair Amplifier' (I like that name
) schematic is dated the 9th March 03, which still means that your RH84 predates it. The John Broskie article was published in March 2001, so I'm not sure if the RH84 predates that since the RH84 schematic is dated '2001'. Nonetheless, the Radiotron Designers' Handbook (4th edition), in which this topology is described, predates both designs by almost fifty years. It apparently was also somewhat popular in the AF output stage of vintage radios. It may very well have been an original idea to you, but whoever thought of it first, or built the first amp based on it does not matter, and in any case is most unlikely to have been you, Gary Pimm, or for that matter, John Broskie.various
Jason,
you are not on the list of axe grinders... but if you look around on the forum, there are some guys causing havoc... and for a moment or so, I was not sure whether I missed something, is it me... or just other guys being very very impolite to others...
When I was 5, I "invented" the relay switch -- ridiculos as it is, do not ask me how. At 5 you cannot know relay switches exist, but I had to envisage the way to radio-control my immaginary submarine... etc. Now, it is more than obvious that I did not invent the relay switch back in 1969. but nevertheless -- to me it does not matter, since I knew there should be something like that in that particular place to do the job.
It does not matter who was there first (files created in CM can be shown to outdate the mentioned events... as well as mail were the circuit was included... but they can be false as well) -- what matters is that we make the most of it!
Brian,
Miroslav Ivanek has had the chance to listen to one of the RH84 clones (the one shown on my site as built by M.S.). They auditioned it on one of his loudspeakers. I do not recall the exact comments, but he stated that it was a good amp. Well, I do not expect they all fell for it, since it was compared with a 45 amp in a system where power is no issue... but I seem to recall that bass was great.
I am familiar with Mr. N.V.'s book... I use to call it "textbook: find the mistake". Not that there are many mistakes in it -- just there is not much originality and of course a lot of the proposed schematics are not to my liking or taste (current draw, general idea, etc.). But I cannot say more than that -- when I need some socket or anything, Mr. Vukusic is the nearest "source" where I can acquire such items
Regards to all,
Aleksandar
Jason,
you are not on the list
of axe grinders... but if you look around on the forum, there are some guys causing havoc... and for a moment or so, I was not sure whether I missed something, is it me... or just other guys being very very impolite to others...When I was 5, I "invented" the relay switch -- ridiculos as it is, do not ask me how. At 5 you cannot know relay switches exist, but I had to envisage the way to radio-control my immaginary submarine... etc. Now, it is more than obvious that I did not invent the relay switch back in 1969. but nevertheless -- to me it does not matter, since I knew there should be something like that in that particular place to do the job.
It does not matter who was there first (files created in CM can be shown to outdate the mentioned events... as well as mail were the circuit was included... but they can be false as well) -- what matters is that we make the most of it!
Brian,
Miroslav Ivanek has had the chance to listen to one of the RH84 clones (the one shown on my site as built by M.S.). They auditioned it on one of his loudspeakers. I do not recall the exact comments, but he stated that it was a good amp. Well, I do not expect they all fell for it, since it was compared with a 45 amp in a system where power is no issue... but I seem to recall that bass was great.
I am familiar with Mr. N.V.'s book... I use to call it "textbook: find the mistake". Not that there are many mistakes in it -- just there is not much originality and of course a lot of the proposed schematics are not to my liking or taste (current draw, general idea, etc.). But I cannot say more than that -- when I need some socket or anything, Mr. Vukusic is the nearest "source" where I can acquire such items
Regards to all,
Aleksandar
Re: various
I guess the speakers were the Veliki prototypes. Great bass indeed!
I have a copy but of course all I can hope to understand are the diagrams!
Seems a nice intro for beginners in this hobby of ours, though agreed of limited interest to more experienced constructors.
Shame there's no English translation.
Brian.
I guess the speakers were the Veliki prototypes. Great bass indeed!
I am familiar with Mr. N.V.'s book... I use to call it "textbook: find the mistake". Not that there are many mistakes in it -- just there is not much originality and of course a lot of the proposed schematics are not to my liking or taste (current draw, general idea, etc.). But I cannot say more than that -- when I need some socket or anything, Mr. Vukusic is the nearest "source" where I can acquire such items
I have a copy but of course all I can hope to understand are the diagrams!
Seems a nice intro for beginners in this hobby of ours, though agreed of limited interest to more experienced constructors.
Shame there's no English translation.
Brian.
Alex, I'm not familiar with RH or T-Rex, but I do know that the gain of the output stage will not change if the driver tube is removed. Could explain what you mean by "it does not work the same way"?
EDIT: I looked at the RH84 schematic and yes, there will be some gain change if the driver is removed. The driver's plate resistor is effectively in parallel with the source impedance of the driver tube. But, the feedback around the output tube is still there and in fact increases.
EDIT: I looked at the RH84 schematic and yes, there will be some gain change if the driver is removed. The driver's plate resistor is effectively in parallel with the source impedance of the driver tube. But, the feedback around the output tube is still there and in fact increases.
I glanced more carefully at GP's feedback method and saw a few items of interest. First, plate to grid feedback reduces output PSU noise. Whatever such noise appears at the output tube plate also appears, in same phase, at the output grid, where it is amplified in opposite phase to thus cancel, to some degree, the original noise signal. Cancellation is only effective, it seems, to the limited extent allowed by some small but necessary phase shift in the opposite-phase signal.
Noise cancellation is good. However, noise cancellation using a slightly out of phase cancelling-signal will leave a residual, which probably doesn't sound good at all.
The second item of interest is that the output AC signal---that precious, sought-after thing---appears, at reduced level, at the driver plate to there modulate the driver signal, to some small but, in my mind, probably not inconsequential degree. Ouch.
Feedback's a tough game, no?
Noise cancellation is good. However, noise cancellation using a slightly out of phase cancelling-signal will leave a residual, which probably doesn't sound good at all.
The second item of interest is that the output AC signal---that precious, sought-after thing---appears, at reduced level, at the driver plate to there modulate the driver signal, to some small but, in my mind, probably not inconsequential degree. Ouch.
Feedback's a tough game, no?
feedback
SY,
you said it yourself -- if you take out the driver, the feedback will change... that's it. In the T-Rex (just follow the thread, you will find a link) the feedback is "independant" of the driver (almost, if anything is indipendant of anything, anyway).
To put it on a brighter side... calculus aside... if you take out the driver, the RH amps will not work... will not amplify any signal that was injected from the input to the circuit. OK, if you connect the signal directly to the output tube's griD, it will be reproduced, but that would be a different amp, feedback or no feedback. In the case of the T-Rex, it is different -- provided you inject a signal directly to the output tube's grid, it will reproduce it just the same as if it was the driver injecting it (calculus of driver output impedance etc. aside).
Brian,
it's not a shame. His language is flamboyant, almost artistic -- but far from really interesting or true. On the other hand, almost all of the examples can be found on the net. Actually, I heard he did find all the examples on the net... But, come on -- is it that important? To gossip about dear old Mr. Vukusic, my neighbour and occasional supplier of tubes and sockets? To tell you the truth, he is the only person I know in Belgrade circles who actually understands what am I telling him about tubes and circuits, and with whom I can have a reasonable discussion on merits. Enough said.
With "great bass" I was not commenting his speakers, but stating what I heard was their comment on the sound of the little RH amp... if you did not get that at first. His speakers? Never heard them, but would be interested. Bear in mind that Mr. Ivanek is a dealer and seller -- first; only after that comes the audiophile in him. Knowing our countries, he is one of those persons who saw an opportunity (market void) and seized upon it. Good on him -- but I sincerely doubt that this is the place to discuss his audiophile merit.
Regards to all,
Aleksandar
SY,
you said it yourself -- if you take out the driver, the feedback will change... that's it. In the T-Rex (just follow the thread, you will find a link) the feedback is "independant" of the driver (almost, if anything is indipendant of anything, anyway).
To put it on a brighter side... calculus aside... if you take out the driver, the RH amps will not work... will not amplify any signal that was injected from the input to the circuit. OK, if you connect the signal directly to the output tube's griD, it will be reproduced, but that would be a different amp, feedback or no feedback. In the case of the T-Rex, it is different -- provided you inject a signal directly to the output tube's grid, it will reproduce it just the same as if it was the driver injecting it (calculus of driver output impedance etc. aside).
Brian,
it's not a shame. His language is flamboyant, almost artistic -- but far from really interesting or true. On the other hand, almost all of the examples can be found on the net. Actually, I heard he did find all the examples on the net... But, come on -- is it that important? To gossip about dear old Mr. Vukusic, my neighbour and occasional supplier of tubes and sockets? To tell you the truth, he is the only person I know in Belgrade circles who actually understands what am I telling him about tubes and circuits, and with whom I can have a reasonable discussion on merits. Enough said.
With "great bass" I was not commenting his speakers, but stating what I heard was their comment on the sound of the little RH amp... if you did not get that at first. His speakers? Never heard them, but would be interested. Bear in mind that Mr. Ivanek is a dealer and seller -- first; only after that comes the audiophile in him. Knowing our countries, he is one of those persons who saw an opportunity (market void) and seized upon it. Good on him -- but I sincerely doubt that this is the place to discuss his audiophile merit.
Regards to all,
Aleksandar
RH88 (6550) in DC mode
Well, I mentioned I wanted to try this version of it... but I did not expect the results would be "this rewarding"... see for yourself. To me, this is a scoop... and I am going to try it as soon as I figure how to achieve 600V B+ (that is going to need some serious thinking on how to use the available transformers and caps...).
Any comments?
Well, I mentioned I wanted to try this version of it... but I did not expect the results would be "this rewarding"... see for yourself. To me, this is a scoop... and I am going to try it as soon as I figure how to achieve 600V B+ (that is going to need some serious thinking on how to use the available transformers and caps...).
Any comments?
Attachments
Re: Off Topc
sorry for interrupting ;
I have opportunity to meet Mr. Vukusic few times on Technical and Electronics Fair at Novi Sad ;
also ,I have opportunity to hear his VT4C SE monoblocks driving KHs;
what I can say - from personal contacts and from hearnig one pair of lousy tube amps ,I can say that (FOR ME) Mr. Vukusic is one old fart (I beg moderators to take it easy )
He take audio too much on personal plan -this hobby (or proffesion for some of us ) for him is kind of personal afirmation,not kind of passion.
Brian Clark said:
sorry for interrupting ;
I have opportunity to meet Mr. Vukusic few times on Technical and Electronics Fair at Novi Sad ;
also ,I have opportunity to hear his VT4C SE monoblocks driving KHs;
what I can say - from personal contacts and from hearnig one pair of lousy tube amps ,I can say that (FOR ME) Mr. Vukusic is one old fart (I beg moderators to take it easy
)He take audio too much on personal plan -this hobby (or proffesion for some of us ) for him is kind of personal afirmation,not kind of passion.
audiousername said:Gary's original PP 47 'Inverse Feedback Pair Amplifier' (I like that name
Back in the summer of 1993, Sound Practices published this:
Attachments
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.