Home |
Search |
Today's Posts |
#1
|
|||
|
|||
Local Cathode FB, UL Tap at Ground Part 2
Here is a version posted by Yves Monmagnon & his collaberators Tomcik & Wiggins to RAT on Sep 1/ 2004.
Hey Patrick, it looks like Yves has you beat by a few years. Such is life. Think of Darwin & Alfred Wallace on evolution. Few people remember Wallace. Or what about Edison & the Brit Swan & the incandescent light? Swan is now mostly forgotten except for their joint company Ediswan in the UK. And development of the first jet engine(s), independantly in the UK & Germany, only a few moths apart. Cheers to all, John |
#2
Posted to rec.audio.tubes
|
|||
|
|||
Local Cathode FB, UL Tap at Ground Part 2
On 12 Nov, 10:16, John L Stewart
wrote: Here is a version posted by Yves Monmagnon & his collaberators Tomcik & Wiggins to RAT on Sep 1/ 2004. Hey Patrick, it looks like Yves has you beat by a few years. Such is life. Think of Darwin & Alfred Wallace on evolution. Few people remember Wallace. Or what about Edison & the Brit Swan & the incandescent light? Swan is now mostly forgotten except for their joint company Ediswan in the UK. And development of the first jet engine(s), independantly in the UK & Germany, only a few moths apart. Cheers to all, John I am lucky to invent things a few moths apart from other dudes. One mustn't let moths into one's mind lest the intellectual larvae eat holes in one's thorts and you end up with many holes in ideas, and empty sockets on amps you try to build, and not knowing why :-) But yeah, Yves beat me alright. I wonder who beat him maybe 40 years ago, but only to also be ignored by everyone, and forgotten so much more quickly due to an absense of searchable Internet stuff? But Yves is using a 6V6 only, and has an unbypassed screen, with its Eg2 supplied through 15k and adjustable pot. That just doesn't look right. If g2 is bypassed to cathode, circuit becomes pure beam tetrode with CFB, and isn't too bad, except for tetrode spectra that still is there, but merely reduced by the NFB. Better, IMHO, is to have a shunt regged and fixed Eg2 at about 3/4 the anode B+. Then the supply R to g2 don't load the anode circuit, and NFB is applied to g2 circuit because the 6V6 works as 20% UL in terms of its open loop gain. Trouble is that hardly any OPTs with a 20% UL tap are ever made. But quite a few are supplied with 40% tap. To then avoid having huge grid drive voltages = say 50% of the Vak, the load value is kept a bit on the lowish side, so that PO is high for the equation PO = Va-k squared / RLa. Say you have 2 x EL34. Loads are Typically 3k6 per tube, so for 2 parallel tubes the RLa = 1k8, and for the 18 Watts easily available you have Va-k = 180Vrms, so that 40% tap gives Vk-0V = 72V, and Vg-0V = 90Vrmsd, not too hard to do with an 6EH7 with about 10mA and CCS in triode and with gain = 45, so Vin without NFB = 2Vrms. Rout with 40% CFB is low enough to not use GNFB, but that's also easy to do if needed if driver = EL84 and a secind paralleled 6CG7 input tube is used with normal type GNFB, and only 9dB max NFB is needed to make sensitivty about a volt. I guess if I tried to get to the moon before 1969, the yanks wooda spent yet more dough and beat me and the Ruskies! Patrick Turner. +-------------------------------------------------------------------+ |Filename: Yves Monmagnon SE 6V6 UL Tap to Ground Page 7W.jpg * * * | |Download:http://www.audiobanter.com/attachment.php?attachmentid=314| +-------------------------------------------------------------------+ -- John L Stewart |
#3
|
|||
|
|||
Quote:
But lots of other problems! Cheers, John |
#4
Posted to rec.audio.tubes
|
|||
|
|||
Local Cathode FB, UL Tap at Ground Part 2
On 14 Nov, 01:24, John L Stewart
wrote: patrick-turner;963845 Wrote: On 12 Nov, 10:16, John L Stewart wrote:- Here is a version posted by Yves Monmagnon & his collaberators Tomcik & Wiggins to RAT on Sep 1/ 2004. Hey Patrick, it looks like Yves has you beat by a few years. Such is life. Think of Darwin & Alfred Wallace on evolution. Few people remember Wallace. Or what about Edison & the Brit Swan & the incandescent light? Swan is now mostly forgotten except for their joint company Ediswan in the UK. And development of the first jet engine(s), independantly in the UK & Germany, only a few moths apart. Cheers to all, John- I am lucky to invent things a few moths apart from other dudes. One mustn't let moths into one's mind lest the intellectual larvae eat holes in one's thorts and you end up with many holes in ideas, and empty sockets on amps you try to build, and not knowing why :-) But yeah, Yves beat me alright. I wonder who beat him maybe 40 years ago, but only to also be ignored by everyone, and forgotten so much more quickly due to an absense of searchable Internet stuff? But Yves is using a 6V6 only, and has an unbypassed screen, with its Eg2 supplied through 15k and adjustable pot. That just doesn't look right. If g2 is bypassed to cathode, circuit becomes pure beam tetrode with CFB, and isn't too bad, except for tetrode spectra that still is there, but merely reduced by the NFB. Better, IMHO, is to have a shunt regged and fixed Eg2 at about 3/4 the anode B+. Then the supply R to g2 don't load the anode circuit, and NFB is applied to g2 circuit because the 6V6 works as 20% UL in terms of its open loop gain. Trouble is that hardly any OPTs with a 20% UL tap are ever made. But quite a few are supplied with 40% tap. To then avoid having huge grid drive voltages = say 50% of the Vak, the load value is kept a bit on the lowish side, so that PO is high for the equation PO = Va-k squared / RLa. Say you have 2 x EL34. Loads are Typically 3k6 per tube, so for 2 parallel tubes the RLa = 1k8, and for the 18 Watts easily available you have Va-k = 180Vrms, so that 40% tap gives Vk-0V = 72V, and Vg-0V = 90Vrmsd, not too hard to do with an 6EH7 with about 10mA and CCS in triode and with gain = 45, so Vin without NFB = 2Vrms. Rout with 40% CFB is low enough to not use GNFB, but that's also easy to do if needed if driver = EL84 and a secind paralleled 6CG7 input tube is used with normal type GNFB, and only 9dB max NFB is needed to make sensitivty about a volt. I guess if I tried to get to the moon before 1969, the yanks wooda spent yet more dough and beat me and the Ruskies! Patrick Turner. - +-------------------------------------------------------------------+ |Filename: Yves Monmagnon SE 6V6 UL Tap to Ground Page 7W.jpg * * * | |Download:http://www.audiobanter.com/attachment.php?attachmentid=314| +-------------------------------------------------------------------+ -- John L Stewart- It seems Yves was a busy guy back there 8 years ago. Here is another of his thoughts. The 4CX250 needs forced air cooling so having the plate at ground would help. But lots of other problems! Cheers, John +-------------------------------------------------------------------+ |Filename: Yves Monmagnon PP 4CX250 Plates at Ground Page 7W.jpg * *| |Download:http://www.audiobanter.com/attachment.php?attachmentid=315| +-------------------------------------------------------------------+ -- John L Stewart- Hide quoted text - - Show quoted text - Upside down tubes look queer, and one might almost think the PNP tube had been invented, which would be so handy to have, considering all known tubes are npn types :-) The 4CX250 data is a bit thin on ground, but appears to have Pda rating of 250W, so I guess 300W from a pair is OK. But its always possible to have tubes such as 6L6GC or a KT120 etc "upside down" and have anode and OPT primary at 0V, and have the whole cathode and its cathode bias R&C and grid at at -400Vdc. The drive to grid is then via IST like Yves has in his schema. Triode operation means the screen is also taken to 0V. So the cathode os where Va appears relative to 0V. Filamants must also float at cathode Vdc bias of say -400V. So one still ends up with up to 800pkV during normal use between pins 3 and 2, so 807 are probably most suitable. I see no problem having a floating HT winding and B+ supply, and I have no problem with Circlotron topology, especially with OTL designs where two equal amplitude phases are used to drive OP devices, and easily produced by an LTP. Having a B+ supply between an anode and an earthy OPT seems a natural way to go to avoid having say 1,000Vdc across insulation of OPT. In my 55 Watt class SE845 amps I ended ed up using split supply rails, +600V and -600V which seemed a fairly good way to do it at the time. As I think about it now, for SET etc, having a floating B+ between earthy primary and anode with +ve anode allws for possibility of having the secondary in series with anode winding to convert the isolationg tranny into an autotranny, and thus slightly changing the turn ratio to a larger one giving higher anode loads ohms with the same Sec load. The 100mAdc flow through sec windings of perhaps Rw = 0.24ohms gives 0.024Vdc at Vo, which would worry some because they don't like any DC in speakers, but 0.024Vdc across 8 ohm voice coil hardly does anything. But the grounded SE OPT with UP primary tap begs for someone to ground the tap, and have say 40% of Va-k at cathode and thus have CFB. But adding sec in series with primary is then impossible lest you have 2 speaker OP terminals each with high Vac-0V signal which is dangerous. Auto transformers are usually wound with one long winding with taps out for smaller than the voltage input across all the winding. If one applies this idea for an OPT where a typical TR is say 25:1, ie, 5k0:8 ZR, then one may think its OK to just use 1/25 of the primary turns to power an 8 ohm speaker. But it ain't. Even though auto tranny is said to be more efficient, the current in shared winding is speaker output current - un-shared primary input current, and where such a big difference between Ia and Iout exists, you still have high current in the shared winding. And the HF coupling is also very poor, despite the direct series connection between the the P and S windings. However, auto trannies are very useful and sensible for where step down is no more than say 4:1, giving say 64r : 4r, which means using a quad of 6C33C in circlotron makes an awesome amp because each tube effectivle is loaded by 256 ohms in class A, an ideal load, and one that does not cause smoke when OTL is attempted. Now, the very curly question I have to ask is how does one design the auto tranny to give best low leakage inductance and lowest winding resistance losses? One mat cite McIntosh and others who have done it, and the guy at www.zeroimepedance.com and he uses a toroid, and what appears to be a few windings all the same and with taps all paralleled and wound on top of each other. But where is the design theory. Its different to what one would use for an E&I. I don't want to know about other products I could buy, but about how to design for myself. I've got along that path for isolation trannies, but not for auto trannies. Looking in Google, I didn't find much except I did notice stuff about apps in large 3 phase PTs. Nothing about how to make a decent audio auto tranny OPT. autot high powrba byhow other L nd ds Like some things, one has to just wind and measure, and maybe use of bifilar is required. But the 'zero impedance' load matchig trannys are supplied to audiophules to make their 4 ohm speakers look like 16 ohms or 32 ohms to an amplifier, so Pda is much reduced and tube in OTL don't smoke, THD is lowered while DF is raised, and the Phules end up realising OPTs ain't so bad after all. I tested a zeroimpedance tranny, and found bandwidth was from about 3Hz up to 1MHz, quite excellent, and surprising considering how rough and untidy the turns look on the toroid. But most toroidal OPTs wih normal isolation windings for say 5k0:8 have hopelessly high shunt C between pri and sec, often 20 times what a 1/2 decent normal E&I tranny has, and seems its because they just don't understand the need to use thicker insulation between windings with high Pd changes between them. They must use Chinese Fools who only work up to 60Hz, and who hate the price of insulation, and the time to takes to put it in proper. Of couse nobody uses woven insulation on toroids to allow varnish to soak right in easily. But varnish increase effective thickness of insulation to increase the dielectric constant so thus increasing effective C. AAAAHHHH, who said working with stuff above 5kHz was to be easy? But I am digressing of course..... But I'd like to add another page to my website on auto trannies. They are not bad things for circlotron designs using mosfets with the same NPN structure so that PP class A then becomes quite awesomely linear. Taps on auto tranny and each side of CT at 0V give zero Vdc at V0, and one should be able to have a good range of load matches without high winding losses or HF loss. Patrick Turner. |
Reply |
Thread Tools | |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Forum | |||
To ground or to cathode? | Vacuum Tubes | |||
Audio Ground 10 ohms above powersupply ground?? | Vacuum Tubes | |||
Floating ground to common ground question. | Car Audio | |||
why rca ground isolators just sound better than cleaning ground points | Car Audio | |||
Ground Zero, Part Deux | Audio Opinions |