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#1
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Full wave bridge with half wave rectifiers
I am building a high voltage (1000VDC +)full wave bridge using half wave
rectifiers. Do I need separate filament supplies for each rectifier? Steve |
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#2
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In article , "Steve Dolan"
wrote: I am building a high voltage (1000VDC +)full wave bridge using half wave rectifiers. Do I need separate filament supplies for each rectifier? Typically three filament supplies are needed, one for the two tubes whose cathodes are connected and provide the positive output leg of the supply, with two separate filament supplies for each of the two tubes supplying the negative output leg of the supply. Regards, John Byrns Surf my web pages at, http://users.rcn.com/jbyrns/ |
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#3
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It depends on the tubes ......
I would use 4x PY500A for that , I think ..... You'll need just 1 winding , 42V / 1.2A , 84V / 0.6A or 168V / 0.3A . Ronald . "Steve Dolan" schreef in bericht ... I am building a high voltage (1000VDC +)full wave bridge using half wave rectifiers. Do I need separate filament supplies for each rectifier? Steve |
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#4
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Steve Dolan wrote: I am building a high voltage (1000VDC +)full wave bridge using half wave rectifiers. Do I need separate filament supplies for each rectifier? Steve You need three filament supplies minimum, Steve, to make a bridge with four rectifier tubes, connected one filament supply shared between the two positive output tubes, one fil supply for each of the tubes from the junction of whose plates you take the negative line (because if you connect their heaters via a single filament supply you provide a connection that subvents the function of the bridge). However, why are you even considering the cost, weight, wiring, heat, real estate demands, not to mention general nuisance of a conventional all-tube bridge? There is an easy way to have all the benefits of a tube bridge without the downsides I listed. You need two halfwave rectifier tubes (6D22S is good amd I also like the 5R4WGB, a military spec, though it is getting expensive) or a single fullwave rectifier tube as in (two diodes in a single envelope (I like the GZ37, still available as the military CV678, or its shortass brother the GZ34), plus two suitable heavy duty silicon rectifiers (BY228, someone on RAT will give you the American equivalent number). This composite transistor/tube group is called a Graetz Bridge. The noise of the two silicon diodes is blocked by the the two tube diodes. Everything is in the circuit, of course, but the circuit is so arranged that the silicon diode noise disappears into thin air, in this case literally because the vacuum inside the tube, unless perfect (too unlikely for words), is simply very, very thin air. A worked application is at Jute on Amps http://members.lycos.co.uk/fiultra/JUTE%20ON%20AMPS.htm and scroll down to T39-KISS-300B-Ultrafi-crct.jpg I have built four-tube rectifiers bridges for kilovolt amps and later replaced them by Graetz bridges as above. I hear no difference. Not do others with a lot of experience. As you can see on the circuit I reference as an application, I also use Graetz bridges on 300B and other amps for the use of golden ears and no one has ever complained. HTH. Andre Jute The master engineer as cost cutter: I saved the planet already today. (Don't worry about the sig, Steve, it is just a provocation for the resident mouth-foamers.) |
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#5
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Ronald wrote: It depends on the tubes ...... I would use 4x PY500A for that , I think ..... You'll need just 1 winding , 42V / 1.2A , 84V / 0.6A or 168V / 0.3A . Ronald . "Steve Dolan" schreef in bericht ... I am building a high voltage (1000VDC +)full wave bridge using half wave rectifiers. Do I need separate filament supplies for each rectifier? Steve What about the H-K insulation in that hookup? Might be some failures!! JLS |
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#6
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" wrote: Steve Dolan wrote: I am building a high voltage (1000VDC +)full wave bridge using half wave rectifiers. Do I need separate filament supplies for each rectifier? Steve You need three filament supplies minimum, Steve, to make a bridge with four rectifier tubes, connected one filament supply shared between the two positive output tubes, one fil supply for each of the tubes from the junction of whose plates you take the negative line (because if you connect their heaters via a single filament supply you provide a connection that subvents the function of the bridge). However, why are you even considering the cost, weight, wiring, heat, real estate demands, not to mention general nuisance of a conventional all-tube bridge? There is an easy way to have all the benefits of a tube bridge without the downsides I listed. You need two halfwave rectifier tubes (6D22S is good amd I also like the 5R4WGB, a military spec, though it is getting expensive) or a single fullwave rectifier tube as in (two diodes in a single envelope (I like the GZ37, still available as the military CV678, or its shortass brother the GZ34), plus two suitable heavy duty silicon rectifiers (BY228, someone on RAT will give you the American equivalent number). This composite transistor/tube group is called a Graetz Bridge. The noise of the two silicon diodes is blocked by the the two tube diodes. Everything is in the circuit, of course, but the circuit is so arranged that the silicon diode noise disappears into thin air, in this case literally because the vacuum inside the tube, unless perfect (too unlikely for words), is simply very, very thin air. A worked application is at Jute on Amps http://members.lycos.co.uk/fiultra/JUTE%20ON%20AMPS.htm and scroll down to T39-KISS-300B-Ultrafi-crct.jpg I have built four-tube rectifiers bridges for kilovolt amps and later replaced them by Graetz bridges as above. I hear no difference. Not do others with a lot of experience. As you can see on the circuit I reference as an application, I also use Graetz bridges on 300B and other amps for the use of golden ears and no one has ever complained. HTH. Andre Jute The master engineer as cost cutter: I saved the planet already today. (Don't worry about the sig, Steve, it is just a provocation for the resident mouth-foamers.) You are right about 3 fil supplies. They need good insulation as well. There is nothing like going the whole hog, and using four 866 mercury vapour rectifiers just to get maximum glowave brights in a lounge. But I really can't see too much wrong with using an all SS bridge but with each SS diode consisting of 3 series 1000piv rated diodes, to be sure to be sure, 12 diodes in total. To stop noise, use appropriate seris R and some caps, to prevent large current pulses charging a cap, or a group of series caps. A choke input filter avoids the current pulses of a capacitor input, but a large well made choke is needed. I only use cap input filters and SS rectifiers and I add series R to limit charge current pulses. There is no noise from rectifiers on the output. There is not even any noise in the SS amps I occasionally build with large caps in the supplies and no series current limiting resistances, and no snubber caps across the diodes. But I do try to screen off the rectifiers inside a box for the PS. What keeps PS noise low is good layout, screening, earth path rightness, and adequate rail filtering. I never use oil caps, and am quite happy using el cheapo plain non fast SS diodes and generic electrolytic caps with LARGE C values, and good ripple current and low esr ratings. I tried "fast recovery rectifiers" and got NO magical improvements that I could detect. The electro caps now made for arduous work in SMPS are usually much better than 1955 caps which gave electros their bad reputation. I don't bother with Black Gates and other expensive brands. The war against electros is almost entirely irrational, imho. It ain't what ya got that does the trick, its how ya use it! Patrick Turner. |
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#7
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Patrick Turner wrote in
: But I really can't see too much wrong with using an all SS bridge but with each SS diode consisting of 3 series 1000piv rated diodes, to be sure to be sure, 12 diodes in total. To stop noise, use appropriate seris R and some caps, to prevent large current pulses charging a cap, or a group of series caps. A choke input filter avoids the current pulses of a capacitor input, but a large well made choke is needed. I only use cap input filters and SS rectifiers and I add series R to limit charge current pulses. There is no noise from rectifiers on the output. There is not even any noise in the SS amps I occasionally build with large caps in the supplies and no series current limiting resistances, and no snubber caps across the diodes. But I do try to screen off the rectifiers inside a box for the PS. What keeps PS noise low is good layout, screening, earth path rightness, and adequate rail filtering. I never use oil caps, and am quite happy using el cheapo plain non fast SS diodes and generic electrolytic caps with LARGE C values, and good ripple current and low esr ratings. I tried "fast recovery rectifiers" and got NO magical improvements that I could detect. Patrick Turner. I have found that with no caps on a diode bridge you will get a great deal of noise generated from diode switching in the range 50-300KHz. It is easy to attenuate by a good 20dB with a 100n cap across the ac connections to the bridge. The noise is mainly reflected back to the mains side, and I detect this with a spectrum analyser and a LISN. Even an electrostatic screen and large iron bulk of the mains tranny won't save you from this noise. However, the noise is broadband and outside the audio band, so as long as it does not modulate other equipment it will not be noticaeable. But it is really easy to eliminate with one cap. Have a lok at a schematic for a Tektronix CRO and you will see such an instance. |
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#8
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Geoff C wrote: Patrick Turner wrote in : But I really can't see too much wrong with using an all SS bridge but with each SS diode consisting of 3 series 1000piv rated diodes, to be sure to be sure, 12 diodes in total. To stop noise, use appropriate seris R and some caps, to prevent large current pulses charging a cap, or a group of series caps. A choke input filter avoids the current pulses of a capacitor input, but a large well made choke is needed. I only use cap input filters and SS rectifiers and I add series R to limit charge current pulses. There is no noise from rectifiers on the output. There is not even any noise in the SS amps I occasionally build with large caps in the supplies and no series current limiting resistances, and no snubber caps across the diodes. But I do try to screen off the rectifiers inside a box for the PS. What keeps PS noise low is good layout, screening, earth path rightness, and adequate rail filtering. I never use oil caps, and am quite happy using el cheapo plain non fast SS diodes and generic electrolytic caps with LARGE C values, and good ripple current and low esr ratings. I tried "fast recovery rectifiers" and got NO magical improvements that I could detect. Patrick Turner. I have found that with no caps on a diode bridge you will get a great deal of noise generated from diode switching in the range 50-300KHz. It is easy to attenuate by a good 20dB with a 100n cap across the ac connections to the bridge. There have been amps I have cobbled up only to find some little peaks, or groups of HF rings once for every diode switch off/on. The 0.01 uF caps have rarely if ever been successful in supressing such PS spikes in an amp output. The current surges in the diodes excites the stray C and leakage L of the power tranny, and presto, you got a resonant circuit at 50kHz to 300kHz. Often a 0.05uf 1,000 v straight across the HT secondary, and other larger caps across windings where rectifiers are used. Series diodes so that R = about 6 times the reactance of the cap input also work, so if a 470 uF cap has 3.4 ohms XC at 100 Hz, use about 27 ohms in series, and the peak charge current into that cap will be greatly reduced, and usually so will the mechanical noise in the power transformer. Dissipation in the HT winding relates to I squared x R, so if I is reduced 3 times, the dissipation in the HT winding is reduced. Its in the series R instead, but I'd rather blow a few 5 watt wire wound R rather than blow a power tranny. I spent considerable time building an LCLCL filter to make the mains clean, but with inductors on the last led to the amps I was testing to gain my C-cick accreditation number. The mains thus has 50 ohms Z at over 50 kHz, and at first I have a lot od switching ring noise trying to go back into the mains. A 0.05uF across the HT reduced it by 30 dB and well below the 2 mV permissible stipulated by the authorities. Usually linear PS mounted within all metal enclosures are very easy to have comply with authorities emission requirements and its easy to keep the signal clean. SMPS which charge directly off the mains into a resevoir cap and then take a square wave signal out at 500 kHz are renowned for causing all sorts of bothers. Not in my PC though, where they seem to have the problems all sussed. Not in Halcro amps either. One has to do whatever it takes to keep an amp quiet, and usually its a range of measures, not just one. Having input sockets and wiring or feedback wiring within 100mm of any other wire mains input wiring or wiring near anything connected to a rectifier and thus carrying switching currents is likely to result in noise at the output. So screen things off, loctate things properly, try different positions, star earth, and use shieled wire for FB loops. Merely placing caps across diodes don't do much. The noise is mainly reflected back to the mains side, and I detect this with a spectrum analyser and a LISN. Even an electrostatic screen and large iron bulk of the mains tranny won't save you from this noise. However, the noise is broadband and outside the audio band, so as long as it does not modulate other equipment it will not be noticaeable. But it is really easy to eliminate with one cap. Have a lok at a schematic for a Tektronix CRO and you will see such an instance. Patrick Turner. |
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#9
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Hi John ,
What about the H-K insulation in that hookup? Might be some failures!! JLS Might be , but U-hkp = 6300V http://www.mif.pg.gda.pl/homepages/f...0/p/PY500A.pdf Ronald . |
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#11
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In article , Chris Hornbeck
wrote: On Mon, 23 May 2005 14:08:08 -0500, (John Byrns) wrote: I am building a high voltage (1000VDC +)full wave bridge using half wave rectifiers. Do I need separate filament supplies for each rectifier? Typically three filament supplies are needed, one for the two tubes whose cathodes are connected and provide the positive output leg of the supply, with two separate filament supplies for each of the two tubes supplying the negative output leg of the supply. This is the classic arrangement. It gives zero stress to the rectifiers' h-k junction (and it *is* a junction at those temperatures and spacings. What "h-k junction", he was talking about "filament supplies", not heater supplies. But it also puts large demands on transformer insulation. That's life.. True enough, but they build them for just this purpose, and 1000VDC is relatively low in the big scheme of things. Regards, John Byrns Surf my web pages at, http://users.rcn.com/jbyrns/ |
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#12
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John Byrns wrote: In article , Chris Hornbeck wrote: On Mon, 23 May 2005 14:08:08 -0500, (John Byrns) wrote: I am building a high voltage (1000VDC +)full wave bridge using half wave rectifiers. Do I need separate filament supplies for each rectifier? Typically three filament supplies are needed, one for the two tubes whose cathodes are connected and provide the positive output leg of the supply, with two separate filament supplies for each of the two tubes supplying the negative output leg of the supply. This is the classic arrangement. It gives zero stress to the rectifiers' h-k junction (and it *is* a junction at those temperatures and spacings. What "h-k junction", he was talking about "filament supplies", not heater supplies. But it also puts large demands on transformer insulation. That's life.. True enough, but they build them for just this purpose, and 1000VDC is relatively low in the big scheme of things. But I have seen arcs develop in OPTs and tube sockets with much lower voltages than 1,000v. Even with 300v, arcs can get going. Anything over 300v demands the greatest respect. Patrick Turner. Regards, John Byrns Surf my web pages at, http://users.rcn.com/jbyrns/ |
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#13
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If he's using a PT designed for FW operation (i.e., if it has a CT as
mentioned) in a bridge supply, it is not always certain whether the CT is well-enough insulated from gnd; it often has to be tried to find out, and sometimes the resultant failure comes later on at a less convenient time after transients or similar spikes have begun to break down this often-vulnerable area of the winding. A PT intended for bridge use can be well worth its cost over using a scrounged FW-designed unit. YMMV Contrary to another post, a choke-input arrg't (if even applicable to the OP's need) may effectively use an inexpensive swinging choke at its input, so long as it's critical value at minimum current is sufficient - which is why swingers exist. |
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#14
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Ronald wrote:
Hi John , What about the H-K insulation in that hookup? Might be some failures!! JLS Might be , but U-hkp = 6300V http://www.mif.pg.gda.pl/homepages/f...0/p/PY500A.pdf Ronald . That is REALLY impressive. Obviously, it would work well in the application referenced as you have pointed out. For myself, I prefer to stay with silicon & an appropriate parallel resistor set to force sharing of inverse voltage, as I have now for about 40 years. Last time I used a tube rectifier I think it was of the 5V4 family which I liked very much. That was in a guitar amp. While using a SS rectifier system it is worth noting that the resulting HV DC is still under the control of tubes on it's way to the loudspeaker. That I believe simplifies things a lot so that one can concentrate on the amplifier circuit itself. My opinion, anyway. John Stewart |
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#16
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#17
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