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What's your favourite voltage regs?
I'm appalled by the number of DC power supplies I have to build to
feed the filaments of the DHTs I use (directly heated triodes), which need one supply per tube ideally. I'm using up loads of voltage regs in the process, and wondered which ones "members of the panel" favour. Typical supply is a 60VA 0-12, 0-12 transformer, then on each secondary Schottky bridge, 15,000uf cap, 12v voltage reg and an adjustable reg confugured as a current source. Typical requirement is 7.25v at 1.25A (10Y), but there's also 2.5v at 1.75A (46) and 5v at 1.25A (300b). I'm using LM1084 at present, but sneaking in some 78S12 because they're cheaper. LM1084s have gone up recently, so also interested in cheaper suppliers than Farnell. So - which voltage regs are your fave choices here? Good quality output important, but cost also a consideration. This looks right up Jim's street for starters. |
What's your favourite voltage regs?
In article
, Andy Evans wrote: So - which voltage regs are your fave choices here? Good quality output important, but cost also a consideration. This looks right up Jim's street for starters. FWIW I tried various types of 'IC voltage regulator/stabiliser chip' some years ago and decided I wasn't keen on any of the common types. Too prone to oscillations or excess noise, etc. Newer ones may be better, but I lost interest in using them. :-) So I have tended to use variations on the kind of topology shown on http://www.audiomisc.co.uk/Armstrong/700/730PSU.gif As you can see, the zener sets the nominal voltage, and a capacity multiplier pass device smooths over the noise and gives a slow start/stop. That example was for about +/-20V up to about 100mA, used for the rails in a preamp. But the same topology has been used many times by my old research group for voltages in the few V region at currents up to a few amps, so may serve your purpose. [1] Just alter the components to suit. Make the pass transistor a form of darlington pair if needed. I found a single device was usually fine for currents of the order of an amp or two. But if you need high current the single-pack darlingtons made for cheaper SS amps might well do that well if you wanted. But these may need to be checked for oscillation problems. Main advantages of the topology are low noise and a gradual windup and rundown rather than coming on or going off with a crack. Kinder for your valve heaters, perhaps. You may also like the fact that it has no overall feedback. :-) No idea if it will suit you, but since you mentioned my name... For power amps, though, I always just used a decent transformer and large caps, then designed the amp to reject power line variations. So no need for any active smoothing/stabilisation/regulation. Slainte, Jim [1] e.g. for the PSU for 5-12V 1A Gunn diodes where noise from the PSU needs to be minimal as it would introduce noise sidebands to the 94GHz output. If you want I can see if I can dig out a diagram of the variable and fixed versions used for that, but they are in essence the above. -- Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm Audio Misc http://www.audiomisc.co.uk/index.html Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html |
What's your favourite voltage regs?
Andy Evans wrote: I'm appalled by the number of DC power supplies I have to build to feed the filaments of the DHTs I use (directly heated triodes), which need one supply per tube ideally. I'm using up loads of voltage regs in the process, and wondered which ones "members of the panel" favour. Typical supply is a 60VA 0-12, 0-12 transformer, then on each secondary Schottky bridge, 15,000uf cap, 12v voltage reg and an adjustable reg confugured as a current source. Typical requirement is 7.25v at 1.25A (10Y), but there's also 2.5v at 1.75A (46) and 5v at 1.25A (300b). I'm using LM1084 at present, but sneaking in some 78S12 because they're cheaper. LM1084s have gone up recently, so also interested in cheaper suppliers than Farnell. So - which voltage regs are your fave choices here? Good quality output important, but cost also a consideration. This looks right up Jim's street for starters. Dare you use a switching regulator ? Graham |
What's your favourite voltage regs?
Thanks Jim - I'll look at this solution. Were you thinking something
like a TIP50 device? I have a box full, so that would be handy for lower currents. What would be good for 2A and over (say up to 5A rating)? Did you try the LM1084 types? I guess you didn't like the 78 types and the 317. |
What's your favourite voltage regs?
In article , Jim Lesurf jcgl@st-
and.demon.co.uk scribeth thus In article , Andy Evans wrote: So - which voltage regs are your fave choices here? Good quality output important, but cost also a consideration. This looks right up Jim's street for starters. FWIW I tried various types of 'IC voltage regulator/stabiliser chip' some years ago and decided I wasn't keen on any of the common types. Too prone to oscillations or excess noise, etc. Newer ones may be better, but I lost interest in using them. :-) Shouldn't you valve types be using DC from batteries;?... -- Tony Sayer |
What's your favourite voltage regs?
"Andy Evans" wrote in message ... I'm appalled by the number of DC power supplies I have to build to feed the filaments of the DHTs I use (directly heated triodes), which need one supply per tube ideally. I'm using up loads of voltage regs in the process, and wondered which ones "members of the panel" favour. Typical supply is a 60VA 0-12, 0-12 transformer, then on each secondary Schottky bridge, 15,000uf cap, 12v voltage reg and an adjustable reg confugured as a current source. Typical requirement is 7.25v at 1.25A (10Y), but there's also 2.5v at 1.75A (46) and 5v at 1.25A (300b). I'm using LM1084 at present, but sneaking in some 78S12 because they're cheaper. LM1084s have gone up recently, so also interested in cheaper suppliers than Farnell. So - which voltage regs are your fave choices here? Good quality output important, but cost also a consideration. This looks right up Jim's street for starters. **The LM317 is as good as the 1084, but, if you want really good regulation, you still can't beat the venerable LM723. More inconvenient, but still one of the best performing regulators at reasonable price. For my money, I like the LM317/337 regs. Very cheap, easy to use and v ery high performance. Trevor Wilson |
What's your favourite voltage regs?
if you want really good regulation,
you still can't beat the venerable LM723. Note that I really need an absolute minimum of 2A current handling, so LM723 is out and LM317 is too marginal - tubes need between 1.25 and 1.75A. No virtue in batteries, and a pig to implement. I have tried, but a good current source sounds just as good as long as you can get the hum right down. Keep the suggestions coming!! Andy |
What's your favourite voltage regs?
"Andy Evans" wrote in message ... if you want really good regulation, you still can't beat the venerable LM723. Note that I really need an absolute minimum of 2A current handling, so LM723 is out and LM317 is too marginal - tubes need between 1.25 and 1.75A. **It is a trivial exercise to boost the current of any regulator. Just check out the manufacturer's data sheet. No virtue in batteries, and a pig to implement. I have tried, but a good current source sounds just as good as long as you can get the hum right down. Keep the suggestions coming!! Andy **Use a LM317 and a series pass device. You could use a LM338K, but they're too expensive for a cheapskate like me. For a filament supply, they'll do fine and they're easy to implement. In truth, I have used them in the past. I just don't like to shell out the big Bucks for them. Trevor Wilson |
What's your favourite voltage regs?
"Andy Evans" wrote in message
... if you want really good regulation, you still can't beat the venerable LM723. Note that I really need an absolute minimum of 2A current handling, so LM723 is out and LM317 is too marginal - tubes need between 1.25 and 1.75A. The LM723 was designed to work with a series-pass transistor/ No virtue in batteries, and a pig to implement. I have tried, but a good current source sounds just as good as long as you can get the hum right down. Heavy filamented DHTs were comonly run from raw AC in the old days so I don't know why you think you need to keep the hum "right down". Valve filaments should really be supplied from a voltage, rather than a current, source. The only advantage of feeding them with a current source is that it reduces the switch-on surge, but again with heavy filaments that really isn't an issue. David. |
What's your favourite voltage regs?
On Jan 16, 12:14*pm, Andy Evans wrote:
I'm appalled by the number of DC power supplies I have to build to feed the filaments of the DHTs I use (directly heated triodes), which need one supply per tube ideally. I'm using up loads of voltage regs in the process, and wondered which ones "members of the panel" favour. Typical supply is a 60VA 0-12, 0-12 transformer, then on each secondary Schottky bridge, 15,000uf cap, 12v voltage reg and an adjustable reg confugured as a current source. Typical requirement is 7.25v at 1.25A (10Y), but there's also 2.5v at 1.75A (46) and 5v at 1.25A (300b). I'm using LM1084 at present, but sneaking in some 78S12 because they're cheaper. LM1084s have gone up recently, so also interested in cheaper suppliers than Farnell. So - which voltage regs are your fave choices here? Good quality output important, but cost also a consideration. This looks right up Jim's street for starters. LM338K in the steel case will do all the business you require and last forever. Maybe pricey but worth it for an IC you intend sticking into the furnace that is a tube amp. Good luck. Andre Jute Visit Jute on Amps at http://members.lycos.co.uk/fiultra/ "wonderfully well written and reasoned information for the tube audio constructor" John Broskie TubeCAD & GlassWare "an unbelievably comprehensive web site containing vital gems of wisdom" Stuart Perry Hi-Fi News & Record Review HTH. |
What's your favourite voltage regs?
On Jan 17, 8:20*am, "David Looser"
wrote: "Andy Evans" wrote in message No virtue in batteries, and a pig to implement. I have tried, but a good current source sounds just as good as long as you can get the hum right down. Heavy filamented DHTs were comonly run from raw AC in the old days so I don't know why you think you need to keep the hum "right down". Valve filaments should really be supplied from a voltage, rather than a current, source. The only advantage of feeding them with a current source is that it reduces the switch-on surge, but again with heavy filaments that really isn't an issue. David. Quite. I wrote a long screed on this subject and then trashed it as counterproductive to Andy's purpose. The ultrafidelista generally use AC fils because they sound best, and if they want to regulate the plate voltage, use a constant current loaded shunt regulator made with a bigger tube next to each power tube. But Andy's on a learning curve, and he won't know that all this regulation is a bridge too far -- I mean the danger of creating an over-refined tube amp that sounds just like a silicon amp but more expensive so -- until he hears it and starts backing off to where he likes the sound. You gotta do it for yourself; that's part of the fun. Andre Jute Arrival is merely the start of the next journey |
What's your favourite voltage regs?
On Jan 16, 7:29*pm, tony sayer wrote:
In article , Jim Lesurf jcgl@st- and.demon.co.uk scribeth thus In article , Andy Evans wrote: So - which voltage regs are your fave choices here? Good quality output important, but cost also a consideration. This looks right up Jim's street for starters. FWIW I tried various types of 'IC voltage regulator/stabiliser chip' some years ago and decided I wasn't keen on any of the common types. Too prone to oscillations or excess noise, etc. Newer ones may be better, but I lost interest in using them. *:-) Shouldn't you valve types be using DC from batteries;?... There are some who do. They hate capacitors so much, they design the entire amp with transformer coupling, and use batteries for power. It's all a question of your commitment to the purity of your sound -- and how many banks of car batteries your wife will let you stack up in the living room. My understanding is that the fellow in Switzerland who drove his anodes with batteries is no longer married. Andre Jute Thumbs well clear of the bricks |
What's your favourite voltage regs?
"tony sayer" wrote in message ... In article , Jim Lesurf jcgl@st- and.demon.co.uk scribeth thus In article , Andy Evans wrote: So - which voltage regs are your fave choices here? Good quality output important, but cost also a consideration. This looks right up Jim's street for starters. FWIW I tried various types of 'IC voltage regulator/stabiliser chip' some years ago and decided I wasn't keen on any of the common types. Too prone to oscillations or excess noise, etc. Newer ones may be better, but I lost interest in using them. :-) Shouldn't you valve types be using DC from batteries;?... -- Tony Sayer Yes - be like my grandfather and toddle off the the local garage once a week to get the accumulator recharged. It somehow seems to fit the ethos of using directly heated triodes 100 years after they were superceded. |
What's your favourite voltage regs?
In article
, Andy Evans wrote: Thanks Jim - I'll look at this solution. Were you thinking something like a TIP50 device? I have a box full, so that would be handy for lower currents. What would be good for 2A and over (say up to 5A rating)? Did you try the LM1084 types? I guess you didn't like the 78 types and the 317. Afraid I can't recall enough details to say. Too long ago that I did the work, and then simply settled for my 'favourite solution'. Not built a PSU like it for some years now. Most recent ones were by my old research students. :-) Slainte, Jim -- Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm Audio Misc http://www.audiomisc.co.uk/index.html Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html |
What's your favourite voltage regs?
In article , tony sayer
wrote: In article , Jim Lesurf jcgl@st- and.demon.co.uk scribeth thus In article , Andy Evans wrote: So - which voltage regs are your fave choices here? Good quality output important, but cost also a consideration. This looks right up Jim's street for starters. FWIW I tried various types of 'IC voltage regulator/stabiliser chip' some years ago and decided I wasn't keen on any of the common types. Too prone to oscillations or excess noise, etc. Newer ones may be better, but I lost interest in using them. :-) Shouldn't you valve types be using DC from batteries;?... The only valves I've done PSUs for were klystrons or carcinotrons. I suspect the battery stacks for those would have been quite large. ;- Slainte, Jim -- Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm Audio Misc http://www.audiomisc.co.uk/index.html Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html |
What's your favourite voltage regs?
"Andy Evans" wrote in
message if you want really good regulation, you still can't beat the venerable LM723. Note that I really need an absolute minimum of 2A current handling, so LM723 is out and LM317 is too marginal - tubes need between 1.25 and 1.75A. LM323 is rated for 3 amps. LM 338 is rated for 5 amps. No virtue in batteries, and a pig to implement. I have tried, but a good current source sounds just as good as long as you can get the hum right down. Agreed. |
What's your favourite voltage regs?
Trevor wrote:
**The LM317 is as good as the 1084, but, if you want really good regulation, you still can't beat the venerable LM723. More inconvenient, but still one of the best performing regulators at reasonable price. For my money, I like the LM317/337 regs. Very cheap, easy to use and v ery high performance. Not very efficient though. Valve amps make enough heat without adding a source inside the chassis. Something with a lower dropout voltage would be good. Also wondering why the OP configures the filament regulator as a current source. More efficient for many filaments because they can be stringed in series, but I can't see why it's better, for a single filament, to use a high-impedance supply. Ian |
What's your favourite voltage regs?
Ian Iveson wrote:
Trevor wrote: **The LM317 is as good as the 1084, but, if you want really good regulation, you still can't beat the venerable LM723. More inconvenient, but still one of the best performing regulators at reasonable price. For my money, I like the LM317/337 regs. Very cheap, easy to use and v ery high performance. Not very efficient though. Valve amps make enough heat without adding a source inside the chassis. Something with a lower dropout voltage would be good. Also wondering why the OP configures the filament regulator as a current source. More efficient for many filaments because they can be stringed in series, but I can't see why it's better, for a single filament, to use a high-impedance supply. Ian The reason I do it that way is it sounds better. I believe the reason it sounds better, is some of the signal appears across the fill in a DHT, and the voltage reg will try and regulate that away, with a current reg, the signal is common mode, so not affected. Voltage reg certainly sounds worst than AC heating, but I think current reg is as good as AC without the problems of AC. Just my theory of course, so expecting to be wrong. -- Nick |
What's your favourite voltage regs?
Andre Jute wrote: The ultrafidelista generally use AC fils because they sound best, Because hum is good for fidelity ? Graham |
What's your favourite voltage regs?
Nick Gorham wrote: Ian Iveson wrote: Also wondering why the OP configures the filament regulator as a current source. More efficient for many filaments because they can be stringed in series, but I can't see why it's better, for a single filament, to use a high-impedance supply. The reason I do it that way is it sounds better. I believe the reason it sounds better, is some of the signal appears across the fill in a DHT, If some of the signal appears across the filament then the regulator isn't doing its job. and the voltage reg will try and regulate that away, with a current reg, the signal is common mode, so not affected. UH ? Voltage reg certainly sounds worst than AC heating, but I think current reg is as good as AC without the problems of AC. Just my theory of course, so expecting to be wrong. How utterly bizarre ! Graham |
What's your favourite voltage regs?
The only advantage of feeding them with a current source is that it
reduces the switch-on surge, but again with heavy filaments that really isn't an issue. David. Quite. I wrote a long screed on this subject and then trashed it as counterproductive to Andy's purpose.Andre Well, it's actually counter to the findings that a bunch of us DHT users observed - current sources sounded better. Have you done direct A-B comparisons? Andy's on a learning curve, and he won't know that all this regulation is a bridge too far -- I mean the danger of creating an over-refined tube amp that sounds just like a silicon amp but more expensive so -- until he hears it and starts backing off to where he likes the sound. You gotta do it for yourself; that's part of the fun. Andre Well, I think we're all on a learning curve. But no way does clean DC make a DHT sound like silicon. I am wondering, as you say, if there are alternatives to voltage regs in the filament supplies, but right now I only see huge caps and chokes - both bigger and heavier and (a lot) more expensive. I'm open to all ideas, since I'm certainly sticking with DHTs for the forseeable future, therefore a lot of filament supplies are my self-imposed fate!!! Incidentally, for the B+ it's all chokes, polypropylene caps and glow tubes. |
What's your favourite voltage regs?
The reason I do it that way is it sounds better. I believe the reason
it sounds better, is some of the signal appears across the fill in a DHT, and the voltage reg will try and regulate that away, with a current reg, the signal is common mode, so not affected. Nick My findings exactly. |
What's your favourite voltage regs?
LM338K in the steel case will do all the business you require and
last forever. Maybe pricey but worth it for an IC you intend sticking into the furnace that is a tube amp. It's a nice product, but around �7 a throw - OK for a one off special but too expensive for continued building. Even the most basic 3 stage all-DHT SET needs 6 filament supplies! |
What's your favourite voltage regs?
On Jan 18, 12:02*am, Andy Evans wrote:
The only advantage of feeding them with a current source is that it reduces the switch-on surge, but again with heavy filaments that really isn't an issue. David. Quite. I wrote a long screed on this subject and then trashed it as counterproductive to Andy's purpose.Andre Well, it's actually counter to the findings that a bunch of us DHT users observed - current sources sounded better. Have you done direct A-B comparisons? I agree, a current sourced regulator sounds better than one without the CC. My point was simply that I consider AC fils good enough sonically. About a dozen years ago, after I gave up on AC balance in PP amps, I spent a lot of time on trying to improve the sound by messing around with the fils. I tried everything including, under the influence of Allen Wright, current sources. I agree that fixing the current is better than fixing the voltage on the fils, but eventually I went back to AC fils because anything more seemed to me to be unnecessary. But don't let that influence you: you still have the pleasures of a simplification kick in front of you! Andy's on a learning curve, and he won't know that all this regulation is a bridge too far -- I mean the danger of creating an over-refined tube amp that sounds just like a silicon amp but more expensive so -- until he hears it and starts backing off to where he likes the sound. You gotta do it for yourself; that's part of the fun. Andre Well, I think we're all on a learning curve. You're right. I didn't mean to sound patronizing. I'm watching you like a hawk in the hope of learning something else I can use on my own amps. But no way does clean DC make a DHT sound like silicon. I have no problem with clean DC. But well-enough filtered DC is clean enough (without necessarily going for those monster caps Patrick Turner advocates). However, if you keep refining everything, the cumulative effect on a DHT is eventually to make it sound over- sophisticated, bland; where that point falls is a matter of taste. I returned to tubes because I switched on the Bang & Olufsen setup in my study one morning and noticed that the music had a chilling quality. Admittedly that edginess of good quality silicon which is subliminally so disturbing is caused by NFB, and the blandness of an overrefined ZNFB DHT amp is of an entirely different nature and of a much lower order, but eventually it just came to me in the library of a grand house one day where I was listening to Steven Doane practice that even fine instruments in expert and sensitive hands have their rough edges, and that the rough edges are what gives them a humane scale that a synthesizer will never share. It is entirely a personal attitude and I offer it only as that. I am wondering, as you say, if there are alternatives to voltage regs in the filament supplies, but right now I only see huge caps and chokes - both bigger and heavier and (a lot) more expensive. I'm open to all ideas, since I'm certainly sticking with DHTs for the forseeable future, therefore a lot of filament supplies are my self-imposed fate!!! I had a bunch of chokes given to me by one of the local hams that were suitable and tried them too. The late Bill May, my technical guy but a music-lover even as he never took his hand off the meter, loved that sound even better than the everything-current-controlled-and-locked- down sound we also tried around that time because we built so many exactly similar amps (at someone else's expensive of course...) to conduct a big transformer comparison, and could then use these amps for other tests. But now you're starting to talk about a lot of real estate that brings other niggling and some rather big problems with it. Incidentally, for the B+ it's all chokes, polypropylene caps and glow tubes. Did I ever tell you what my big T199 "Millennium's End" PSE Svetlana SV572-xx did with the second transmitting tube on the chassis when operated in its lowest (under 10W) SE mode? In that version the second transmitting tube was turned into a shunt regulator for the remaining signal power tube, a very wasteful procedure as a shunt regulator immediately drops as much current as the operating tube -- but the sound was one of the finest I ever heard. I should add that the shunt reg was current-controlled; that was the final 20% trick of what was already a very pleasing sound. But, of course, the heat and the complication and the expense (just try buying an audio-quality switch good to 1000V) and the lack of reliability because a lot of the components were operating on the ragged edge, all of that made me uncomfortable and not just because a kilovolt amp is intrinsically dangerous -- it would make me uncomfortable on a 300B at less than hallf that voltage.. But I learned something: shunt reg sounds better than series reg by so many magnitudes it is no contest. Of course, I'm talking about plate voltage now; I don't quite see anyone shunt regulating all those mansized filament amperes... Such fun to throw out alternatives when someone else is doing the work! Pay no attention to what I liked or didn't, Andy. When it sounds right to you, you're on the right track. And if it doesn't sound as good as another idea, you're still on the right track, just temporarily on a branch line. It's a journey without an end. Andre Jute Visit Jute on Amps at http://members.lycos.co.uk/fiultra/ "wonderfully well written and reasoned information for the tube audio constructor" John Broskie TubeCAD & GlassWare "an unbelievably comprehensive web site containing vital gems of wisdom" Stuart Perry Hi-Fi News & Record Review PS I'm sure you know this already: the original and still the best of the Lundahl power transformers comes with four separate beefy filament supplies. I've always just bought the standard LL1651 and knocked the 6.3V down with a resistor for 5V DHT fils because I believe the resistor provides an element of stabilization, but I should think Per Lundahl will wind them for you with 5V fils if you ask. |
What's your favourite voltage regs?
On Jan 17, 8:05 pm, Eeyore
wrote: Andre Jute wrote: The ultrafidelista generally use AC fils because they sound best, Because hum is good for fidelity ? Graham Yo, Poopsta, you have my sympathy. It must be really distressing living down there in Boombox World as you do among people constantly seeking to add distortion to their music. How many years does one have to spend down there in Audio Hell before you start believing everyone else is a moron without taste or musical education? But your prejudice doesn't apply to people who know what they do with tubes, who have the money for DHT and the skill to apply the accumulated knowledge. Time to start educating you, Poopie. Say after me, one hundred times: Properly implemented DHT DO NOT HUM. Proper implementation almost never requires regulation in DHT. It means paying attention to grounding and to the sizing and physical placement of filament balancing devices (small subcircuits often called humbusters, which is perhaps where you got your silly prejudice). We're not talking about some little guitar-amp with 12AX7 of the sort you are no doubt familiar with, we're talking about the mighty 300B. Proper implementation of 300B fils is shown on my netsite, and probably discussed in one of the chapters of The KISS Amp. I'll leave you find the circuit and the text; at least that'll keep you out of the pub and other dens of vice with boomboxes where you apparently gather the misinformation you spread like disease on UKRA and RAT and the protechtube conferences. Don't bother grovelling in the dirt; a simple deep bow and a sincere "Thank you, Master" will do the business. Andre Jute Charisma is the talent of inducing apoplexy in losers by merely existing elegantly |
What's your favourite voltage regs?
In article , Eeyore
wrote: Nick Gorham wrote: Ian Iveson wrote: and the voltage reg will try and regulate that away, with a current reg, the signal is common mode, so not affected. UH ? Can only speculate at this point as I have never tried using these circuits for heaters in audio amps. However... With 'direct' heating the heater psu is - I presume - connected to the same physical place as the cathode signal. Having a 'constant current' PSU means the PSU looks like a high impedance connection, so will be less likely to have a loading effect on signal drive to the cathode if the PSU common mode isolation is poor. i.e. the problem is that the cathode signal has to drive any loading it sees due to the PSU, so a high impedance might be preferred. Slainte, Jim -- Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm Audio Misc http://www.audiomisc.co.uk/index.html Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html |
What's your favourite voltage regs?
i.e. the problem is that the cathode signal
has to drive any loading it sees due to the PSU, so a high impedance might be preferred. Slainte, Jim Yes, you're right on the nail - that's a common reason given by those who have developed and use current sources - the high impedence. Here is a useful reference on DHT filaments which refers exactly to this. http://www.tentlabs.com/Products/Tub...ent/index.html http://www.tentlabs.com/Products/Tub...ingmethods.pdf |
What's your favourite voltage regs?
"Jim Lesurf" wrote in message ... In article , tony sayer wrote: In article , Jim Lesurf jcgl@st- and.demon.co.uk scribeth thus In article , Andy Evans wrote: So - which voltage regs are your fave choices here? Good quality output important, but cost also a consideration. This looks right up Jim's street for starters. FWIW I tried various types of 'IC voltage regulator/stabiliser chip' some years ago and decided I wasn't keen on any of the common types. Too prone to oscillations or excess noise, etc. Newer ones may be better, but I lost interest in using them. :-) Shouldn't you valve types be using DC from batteries;?... The only valves I've done PSUs for were klystrons or carcinotrons. I suspect the battery stacks for those would have been quite large. ;- **"Carcinotron"? I had to look that one up. A type of travelling wave tube. I thought I'd heard all the names, but the choice of the name: carcinotron was sure an unfortunate one. Trevor Wilson |
What's your favourite voltage regs?
In article , Trevor Wilson
wrote: "Jim Lesurf" wrote in message Shouldn't you valve types be using DC from batteries;?... The only valves I've done PSUs for were klystrons or carcinotrons. I suspect the battery stacks for those would have been quite large. ;- **"Carcinotron"? I had to look that one up. A type of travelling wave tube. I thought I'd heard all the names, but the choice of the name: carcinotron was sure an unfortunate one. It was a common description in my experience. I think at least one of the makers of BWOs (backward wave oscillilators) for 100GHz used it. It may have been Thompson CSF but I can't recall as it was ages ago. I assume it was on the basis that the backward wave was - in conventional TWT terms - a parasitic growth than extracted power from a forward beam mode. Analogy with the way a cancer growth takes resources from the normal body processes or disrupts their operation. So for a conventional TWT it was unwanted, but turned out to be useful for power at higher frequencies. Advantage of the tubes was that you could get them up to about a THz, and they had a wide electronic tuning range. The snag was what brought them to mind for this thread. The wide electronic tuning range meant that you needed to control all the applied voltages with exceptional care if you wanted output stable to a few kHz or better. Slainte, Jim -- Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm Audio Misc http://www.audiomisc.co.uk/index.html Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html |
What's your favourite voltage regs?
"Jim Lesurf" wrote in message
... Can only speculate at this point as I have never tried using these circuits for heaters in audio amps. However... With 'direct' heating the heater psu is - I presume - connected to the same physical place as the cathode signal. Having a 'constant current' PSU means the PSU looks like a high impedance connection, so will be less likely to have a loading effect on signal drive to the cathode if the PSU common mode isolation is poor. i.e. the problem is that the cathode signal has to drive any loading it sees due to the PSU, so a high impedance might be preferred. No, it's nothing to do with loading. What is actually happening is that the resistance of the filament is partially in series with the cathode current. So it acts as an unbypassed cathode resistor creating a little bit of negative feedback. Effectively shorting that out with a low impedence filament supply reduces this negative feedback. David. |
What's your favourite voltage regs?
In article , David Looser
wrote: "Jim Lesurf" wrote in message ... Can only speculate at this point as I have never tried using these circuits for heaters in audio amps. However... With 'direct' heating the heater psu is - I presume - connected to the same physical place as the cathode signal. Having a 'constant current' PSU means the PSU looks like a high impedance connection, so will be less likely to have a loading effect on signal drive to the cathode if the PSU common mode isolation is poor. i.e. the problem is that the cathode signal has to drive any loading it sees due to the PSU, so a high impedance might be preferred. No, it's nothing to do with loading. So if I grounded one of the heater wires it would have no effect on the signal? Are you sure of that? It seems implausible to me, but I haven't done any work on DHT amps for audio. If you have, perhaps you can explain more clearly. Even with indirect heating with insulation between heater and cathode I'd expect some coupling between heater and cathode due to capacitance or inductance, so some (small) effects due to heater PSU loading could arise. Can't presently see why this would be impossible for DHT, I'm afraid. What is actually happening is that the resistance of the filament is partially in series with the cathode current. So it acts as an unbypassed cathode resistor creating a little bit of negative feedback. Effectively shorting that out with a low impedence filament supply reduces this negative feedback. I think we were talking about the use of resistors *external* to the heater element, and in which the signal current would not appear if the PSU were genuinely floating. *Not* the resistance of the valve between its heater terminals. The point of the resistors being to reduce any effect of the PSU not being a perfectly floating one. I suspect you have misunderstood the point that were made, but I will be interested in your reply. Slainte, Jim -- Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm Audio Misc http://www.audiomisc.co.uk/index.html Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html |
What's your favourite voltage regs?
David Looser wrote
Can only speculate at this point as I have never tried using these circuits for heaters in audio amps. However... With 'direct' heating the heater psu is - I presume - connected to the same physical place as the cathode signal. Having a 'constant current' PSU means the PSU looks like a high impedance connection, so will be less likely to have a loading effect on signal drive to the cathode if the PSU common mode isolation is poor. i.e. the problem is that the cathode signal has to drive any loading it sees due to the PSU, so a high impedance might be preferred. No, it's nothing to do with loading. What is actually happening is that the resistance of the filament is partially in series with the cathode current. So it acts as an unbypassed cathode resistor creating a little bit of negative feedback. Effectively shorting that out with a low impedence filament supply reduces this negative feedback. Isn't this just an alternative description of the same phenomenon? How is cathode loading nothing to do with feedback? Whatever, looking at a typical filament circuit, such as the first diagram in this quite interesting article on the reduction of hum due to the thermal effect of AC heating: http://members.aol.com/sbench/humbal.html the parasitic LCR network to ground through the filament supply source is shunted by just a few ohms, in the case of fixed bias, or by that plus the combination of cathode resistor and bypass capacitor, in the case of cathode bias. I am surprised that it ends up being significant. Also, if you replace the floating transformer winding in the illustrated circuit with a voltage source or a current source, also floating, it isn't immediately obvious to me why the one should present a lower impedance to a *common mode* signal than the other. The big difference would be in the impedance presented to a differential mode signal between the ends of the filament. Assuming a DC source allows the hum pot to be dispensed with, and that the two remaining resistors are balanced, there should be no differential mode signal. So I don't see why this should be significant either. So why does it sound better? Ian |
What's your favourite voltage regs?
David Looser wrote: "Jim Lesurf" wrote Can only speculate at this point as I have never tried using these circuits for heaters in audio amps. However... With 'direct' heating the heater psu is - I presume - connected to the same physical place as the cathode signal. Having a 'constant current' PSU means the PSU looks like a high impedance connection, so will be less likely to have a loading effect on signal drive to the cathode if the PSU common mode isolation is poor. i.e. the problem is that the cathode signal has to drive any loading it sees due to the PSU, so a high impedance might be preferred. No, it's nothing to do with loading. What is actually happening is that the resistance of the filament is partially in series with the cathode current. So it acts as an unbypassed cathode resistor creating a little bit of negative feedback. Effectively shorting that out with a low impedence filament supply reduces this negative feedback. Finally some sense. Graham |
What's your favourite voltage regs?
"Ian Iveson" wrote in message
o.uk... David Looser wrote Can only speculate at this point as I have never tried using these circuits for heaters in audio amps. However... With 'direct' heating the heater psu is - I presume - connected to the same physical place as the cathode signal. Having a 'constant current' PSU means the PSU looks like a high impedance connection, so will be less likely to have a loading effect on signal drive to the cathode if the PSU common mode isolation is poor. i.e. the problem is that the cathode signal has to drive any loading it sees due to the PSU, so a high impedance might be preferred. No, it's nothing to do with loading. What is actually happening is that the resistance of the filament is partially in series with the cathode current. So it acts as an unbypassed cathode resistor creating a little bit of negative feedback. Effectively shorting that out with a low impedence filament supply reduces this negative feedback. Isn't this just an alternative description of the same phenomenon? How is cathode loading nothing to do with feedback? Well maybe it is. In which case Jim Lesurf has a very odd way of describing it. Is it usual to describe the function of cathode resistor bypass capacitor in a conventional common-cathode amplifier as "loading the drive signal to the cathode"?, I think not. Also, if you replace the floating transformer winding in the illustrated circuit with a voltage source or a current source, also floating, it isn't immediately obvious to me why the one should present a lower impedance to a *common mode* signal than the other. I agree 100%. The common-mode signal is the signal voltage on the cathode (which will probably be zero anyway, unless an unbypassed cathode resistor is used to provide local negative feedback). But the floating filament supply cannot possibly load this signal even if it exists. The big difference would be in the impedance presented to a differential mode signal between the ends of the filament. Assuming a DC source allows the hum pot to be dispensed with, and that the two remaining resistors are balanced, there should be no differential mode signal. So I don't see why this should be significant either. So why does it sound better? Why indeed?. And why has no one mentioned the effect of reversing the polarity of the filament supply in the DC case? This will make a far larger difference to the operating conditions of the valve than using a current, rather than a voltage, regulated filament supply. Nor do I understand this sudden fashion for *single-ended* amplifiers, when push-pull has been the preferred quality option right from the days when DHTs were the latest technology. David. |
What's your favourite voltage regs?
Nor do I understand this sudden fashion for *single-ended* amplifiers, when
push-pull has been the preferred quality option right from the days when DHTs were the latest technology. David.- Hide quoted text - Very good question. They sound different - push pull cleaner, SET posessing some hard to define factor which many people like. But PLEASE let's not go down that road in this thread - we've been there a zillion times already. The technical discussion of how filament supplies work is most interesting! |
What's your favourite voltage regs?
Ian Iveson wrote:
David Looser wrote Can only speculate at this point as I have never tried using these circuits for heaters in audio amps. However... With 'direct' heating the heater psu is - I presume - connected to the same physical place as the cathode signal. Having a 'constant current' PSU means the PSU looks like a high impedance connection, so will be less likely to have a loading effect on signal drive to the cathode if the PSU common mode isolation is poor. i.e. the problem is that the cathode signal has to drive any loading it sees due to the PSU, so a high impedance might be preferred. No, it's nothing to do with loading. What is actually happening is that the resistance of the filament is partially in series with the cathode current. So it acts as an unbypassed cathode resistor creating a little bit of negative feedback. Effectively shorting that out with a low impedence filament supply reduces this negative feedback. Isn't this just an alternative description of the same phenomenon? How is cathode loading nothing to do with feedback? Whatever, looking at a typical filament circuit, such as the first diagram in this quite interesting article on the reduction of hum due to the thermal effect of AC heating: http://members.aol.com/sbench/humbal.html the parasitic LCR network to ground through the filament supply source is shunted by just a few ohms, in the case of fixed bias, or by that plus the combination of cathode resistor and bypass capacitor, in the case of cathode bias. I am surprised that it ends up being significant. Also, if you replace the floating transformer winding in the illustrated circuit with a voltage source or a current source, also floating, it isn't immediately obvious to me why the one should present a lower impedance to a *common mode* signal than the other. The big difference would be in the impedance presented to a differential mode signal between the ends of the filament. Assuming a DC source allows the hum pot to be dispensed with, and that the two remaining resistors are balanced, there should be no differential mode signal. So I don't see why this should be significant either. So why does it sound better? My badly worded description was trying to suggest that the voltage generated across the fil by the signal would be such that it would not alter the DC current flowing, and the regulator would not be affected by the presence of the signal across the fil. that's what I meany by common mode. In the case of a voltage reg, the signal would be seen as a voltage variation and the regulator would try and track the signal to maintain a constant voltage across the fil. -- Nick |
What's your favourite voltage regs?
"Nick Gorham" wrote in message
... My badly worded description was trying to suggest that the voltage generated across the fil by the signal would be such that it would not alter the DC current flowing, In fact the current flowing through the fil *will* be affected by the signal flowing, part of the signal current will flow through the fil and add to that from the regulated current source. This will be even more the case when the external cathode connection is made to the +ve end of the fil as then most of the signal current flows through the fil. When the fil is driven by a voltage regulator then most of this signal current will flow through the low impedence of the regulator instead. the presence of the signal across the fil. that's what I meany by common mode. Though that's differential mode, not common mode. In the case of a voltage reg, the signal would be seen as a voltage variation and the regulator would try and track the signal to maintain a constant voltage across the fil. Indeed, thus reducing the negative feedback effect of having the signal current flowing through the resistance of the fil. David. |
What's your favourite voltage regs?
In article , David Looser
wrote: "Ian Iveson" wrote in message o.uk... Isn't this just an alternative description of the same phenomenon? How is cathode loading nothing to do with feedback? Well maybe it is. In which case Jim Lesurf has a very odd way of describing it. I think we are talking at cross-purposes. I was dealing with what I thought Andy and Nick were referring to. i.e. external resistors in the heater PSU, or their equivalent in terms of employing a 'constant current' heater PSU. The external resistance would be in series with any the cathode *signal* and the rest of the system via the PSU. You are, I think, talking about the internal resistance in the valve used for heating. I have no idea which of these has any significant in an audio amp. :-) I was simply commenting that if their is some loading via the PSU then resistors would help reduce this. Seen equivalent effects in mm wave oscillator tubes. From the values people quote, though, the heater resistance in the valve seems only to be of the order of 10 Ohms for the DHTs (?) If so, given the other impedances I'd be surprised if that had a significant effect. But as I say, I've not built or studied these types of amp... I agree 100%. The common-mode signal is the signal voltage on the cathode (which will probably be zero anyway, unless an unbypassed cathode resistor is used to provide local negative feedback). But the floating filament supply cannot possibly load this signal even if it exists. The problem Andy/Nick were referring to was, I think, that the PSU is *not* perfectly isolated/floating. However if I have misunderstood, perhaps they can say. Slainte, Jim -- Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm Audio Misc http://www.audiomisc.co.uk/index.html Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html |
What's your favourite voltage regs?
"Jim Lesurf" wrote in message
... In article , David Looser wrote: No, it's nothing to do with loading. So if I grounded one of the heater wires it would have no effect on the signal? Are you sure of that? It seems implausible to me, but I haven't done any work on DHT amps for audio. If you have, perhaps you can explain more clearly. Generally speaking in a common-cathode amplifier the cathode *is* at ground potential as far the signal is concerned. The only exception is when an unbypassed cathode resistor is used to provide local negative feedback. The filament supply is floating with respect to earth so it's not going to load the signal at the cathode anyway. Even with indirect heating with insulation between heater and cathode I'd expect some coupling between heater and cathode due to capacitance or inductance, so some (small) effects due to heater PSU loading could arise. Can't presently see why this would be impossible for DHT, I'm afraid. What is actually happening is that the resistance of the filament is partially in series with the cathode current. So it acts as an unbypassed cathode resistor creating a little bit of negative feedback. Effectively shorting that out with a low impedence filament supply reduces this negative feedback. I think we were talking about the use of resistors *external* to the heater element, and in which the signal current would not appear if the PSU were genuinely floating. I'm not. I'm talking about the resistance of the filament, which is effectively in series with the cathode current *Not* the resistance of the valve between its heater terminals. The point of the resistors being to reduce any effect of the PSU not being a perfectly floating one. Why should the PSU *not* be a perfectly floating one?. We are talking audio here, not HF, and the impedance to ground from the filament will be no more than 100 ohms or so at the outside anyway. I suspect you have misunderstood the point that were made, Whilst it seems to me that your analysis of what is going on is totally flawed. but I will be interested in your reply. As I will be in yours David. |
What's your favourite voltage regs?
In article , David Looser
wrote: "Jim Lesurf" wrote in message ... *Not* the resistance of the valve between its heater terminals. The point of the resistors being to reduce any effect of the PSU not being a perfectly floating one. Why should the PSU *not* be a perfectly floating one?. Because in reality the PSU will exhibit parasitic capacitance, inductances, etc. to its surroundings. For example parasitic capacitance via the transformer windings (or electrostatic screen if present), and via the wires. I'm afraid that in the real world you are unlikely to find a perfectly floating PSU. Just ones which may sufficiently well isolated for a given use. So the effects may be too small to worry about in some cases. But that does not mean they don't exist, or can never have a significant effect. I had assumed you would be aware of this, and would have realised that we were talking about different issues. If you have built and used PSUs you will, I assume, be aware of possible problems with things like interference getting through them, various kinds of parasitic, and how to deal with this. I suspect you have misunderstood the point that were made, Whilst it seems to me that your analysis of what is going on is totally flawed. Well, IIUR, the 'flaw' seems to be that I analysed what Andy and Nick were talking about. Indeed I have had emails to that effect. However maybe we are all out of step except for yourself. :-) As I have pointed out repeatedly, though, I have never built or tested one of the DHT audio amps, so can't comment on how significant these effects may be in them. Can only point out that they exist. FWIW I have encountered them in power tube PSUs of the kind I mentioned where they may affect the control of the tube when using something like a lock loop. Slainte, Jim -- Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm Audio Misc http://www.audiomisc.co.uk/index.html Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html |
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