If there was a 450-0-450 Hammond to recommend I would have. You could just compensate by running more current through the tubes.
Another thing that could be done is run the 500-0-500 with some zeners at CT to cut voltage, I wouldnt want to use a bunch of resistance to cut it. Just keep adding pairs of 6.3V zeners till your about at the voltage you want.
Another thing that could be done is run the 500-0-500 with some zeners at CT to cut voltage, I wouldnt want to use a bunch of resistance to cut it. Just keep adding pairs of 6.3V zeners till your about at the voltage you want.
One thing I might try to do is talk to the friendly folks over at Edcor Transformers ( http://www.edcorusa.com/classx/power/xpwr/xpwr.htm ) and ask them to wire me up a pair of 450V .2A transformers. I'll try to get a 5V winding, but if that doesn't work, Triode Electronics carries 6AU4GT's that will work off the 6.3V winding. The 6AU4GT, according to http://www.mif.pg.gda.pl/homepages/frank/sheets/137/6/6AU4GT.pdf , uses 1.8 amps in the filament. Going off the Edcor's 5A, I still have 3.2 to power 2 6L6WXT+ and the 6SN7GT and 6SL7GT. Sounds good. If the price is prohibitive, I suppose I'll get the 500V Hammonds and use Zeners.
One possibility is that I could just follow the schematic, i.e. go with a 5V4 off a 370VAC winding, followed by their CLC filter, but I figure I'd rather avoid this as I hear that connecting the 5V winding to the output as opposed to getting it straight from the cathode adds a lot of hum?
One possibility is that I could just follow the schematic, i.e. go with a 5V4 off a 370VAC winding, followed by their CLC filter, but I figure I'd rather avoid this as I hear that connecting the 5V winding to the output as opposed to getting it straight from the cathode adds a lot of hum?
new idea
As much as I respect the choke-input PSU, I won't be able to do one without using Zeners as it stands. I've done some more simulating and have found a possible alternative. The attached picture describes the schematic I'm considering.
In case it's hard to read, the capacitor is two 50uF sections of a JJ can. I have a real thing for those sweet JJ cans, they'd look great in an amp
In simulation, maximum current surge in the choke is .17A, well below its .2A tolerance. I'm using 5% regulation on 320VAC into .15A for the PT.
I think that this circuit would work, any thoughts? The only thing that bothers me is that the PT is only good for .15A into the HT, I'd have preferred some more headroom but this seems like it'll work. I'd rather have close to the right voltage than below it, especially if I have to rebias etc.
As much as I respect the choke-input PSU, I won't be able to do one without using Zeners as it stands. I've done some more simulating and have found a possible alternative. The attached picture describes the schematic I'm considering.
An externally hosted image should be here but it was not working when we last tested it.
In case it's hard to read, the capacitor is two 50uF sections of a JJ can. I have a real thing for those sweet JJ cans, they'd look great in an amp
In simulation, maximum current surge in the choke is .17A, well below its .2A tolerance. I'm using 5% regulation on 320VAC into .15A for the PT.
I think that this circuit would work, any thoughts? The only thing that bothers me is that the PT is only good for .15A into the HT, I'd have preferred some more headroom but this seems like it'll work. I'd rather have close to the right voltage than below it, especially if I have to rebias etc.
I have a couple of recommendations. Your P-P amp will draw about 100 mA at idle and hit over 200 mA on peaks (per channel). Most of the peak current is supplied by the caps in the power supply. Therefore it is important to use a cap with a low internal resistance (ESR) and a high peak current capabillity. The motor RUN caps are the best low cost choice here, although they are large. I use the ASC 100 uF 370 VAC caps available on Ebay (about $11USD). They will work at 500 or more DC volts. Wire one of these directly in parallel (or in place of) the last cap in the power supply (the one that connects to the red lead on the OPT).
I have been building 40 to 50 watt P-P guitar amps that get far more abuse than your stereo should ever have to endure. For similar sized amps (one transformer per channel) I used to use Hammond 274BX (750VCT 175mA 60 Hz rated). I have since switched to the Allied (www.alliedelec.com) 6K7VG. This transformer is 750VCT 150mA 50 and 60Hz rated. It is made by Hammond, and quite a bit larger than the 274BX. If operated on 60 Hz you can draw more current. It is also $43 USD. I have used both in guitar amps without failure. Both of these will make about 450 Volts with a cap input using a 5AR4. The voltage can be lowered by using a choke input power supply (use PSUD to find the value of choke). Both of your schematics are correct, however many people use a second choke instead of a resistor. Allied also has low cost (but ugly) chokes.
If you want to feed both channels from one transformer use the big Antek AN-4T360. Another good choice is the 236.5072 from Maryland toroid (www.toroid.com). It is more than twice the price of the Antek and smaller, but it has a 5 volt winding. I get about 425 volts from these using a 5AR4 and cap input. Again choke input will give a lower voltage, less hum, and a happier transformer (less peak current). For an outrageous design use two 5AR4's and seperate power supplies for each channel fed from the same transformer.
It would also be possible to use two seperate SS bridge rectifiers, and complete power supplies on each 360 volt secondary and feed one channel from each supply. The problem here is that the B+ will be ready before the amp tubes are hot. The easiest solution is a standby switch.
The Antek does not have a 5 volt winding, here you have two choices. Use a dropping resistor off of one of the 6 volt windings, or run 6AU4's as you mentioned. I have done both, but I am using 6AX4's because I have a bunch of them. In either case use one 6 volt winding for the rectifiers, and the other for the rest of the amp. This is especially important wirh the 5AR4 since that winding will be connected to B+.
I have been building 40 to 50 watt P-P guitar amps that get far more abuse than your stereo should ever have to endure. For similar sized amps (one transformer per channel) I used to use Hammond 274BX (750VCT 175mA 60 Hz rated). I have since switched to the Allied (www.alliedelec.com) 6K7VG. This transformer is 750VCT 150mA 50 and 60Hz rated. It is made by Hammond, and quite a bit larger than the 274BX. If operated on 60 Hz you can draw more current. It is also $43 USD. I have used both in guitar amps without failure. Both of these will make about 450 Volts with a cap input using a 5AR4. The voltage can be lowered by using a choke input power supply (use PSUD to find the value of choke). Both of your schematics are correct, however many people use a second choke instead of a resistor. Allied also has low cost (but ugly) chokes.
If you want to feed both channels from one transformer use the big Antek AN-4T360. Another good choice is the 236.5072 from Maryland toroid (www.toroid.com). It is more than twice the price of the Antek and smaller, but it has a 5 volt winding. I get about 425 volts from these using a 5AR4 and cap input. Again choke input will give a lower voltage, less hum, and a happier transformer (less peak current). For an outrageous design use two 5AR4's and seperate power supplies for each channel fed from the same transformer.
It would also be possible to use two seperate SS bridge rectifiers, and complete power supplies on each 360 volt secondary and feed one channel from each supply. The problem here is that the B+ will be ready before the amp tubes are hot. The easiest solution is a standby switch.
The Antek does not have a 5 volt winding, here you have two choices. Use a dropping resistor off of one of the 6 volt windings, or run 6AU4's as you mentioned. I have done both, but I am using 6AX4's because I have a bunch of them. In either case use one 6 volt winding for the rectifiers, and the other for the rest of the amp. This is especially important wirh the 5AR4 since that winding will be connected to B+.
My problem as it stands is that either transformers don't have enough voltage, or they're too high. With voltages that are too low, I need to use a capacitor input filter, which jacks up the voltage BUT I blow the 5AR4's current max. in PSUDII if ANY of the capacitors are too big (more than 50uF or so). With voltages that are too high, I use a choke input filter, then have to use a hefty dropping resistor (around 60-watt rating..?) to get voltage down to accceptable levels. With the 282X (500-0-500) I'm getting 435V into .13A after a simple choke input filter with a 193J and 500uF. Would it be bad to feed that much voltage into this schematic?
I guess Edcor _is_ getting that email after all...
I guess Edcor _is_ getting that email after all...
I'm also keeping an eye on these... I simulated these at just under 420V with a capacitor input. I don't expect that feeding 420V into the hafler/keroes will make it fuss very much.
http://cgi.ebay.com/Western-Electri...ryZ67815QQssPageNameZWDVWQQrdZ1QQcmdZViewItem
http://cgi.ebay.com/Western-Electri...ryZ67815QQssPageNameZWDVWQQrdZ1QQcmdZViewItem
You might be able to go with the 500-0-500 choke input by increasing the bias resistors to compensate.
Or use the 425-0-425 choke input, possibly richer with slightly lower bias resistor. Schematic 2 claims a 365V B+, this would actually be pretty close.
I think that WE transformer is 241-0-241. If your willing to use a separate filament xfmr, new industrial control PTs with dual 240V secondaries are a dime a dozen.
Or use the 425-0-425 choke input, possibly richer with slightly lower bias resistor. Schematic 2 claims a 365V B+, this would actually be pretty close.
I think that WE transformer is 241-0-241. If your willing to use a separate filament xfmr, new industrial control PTs with dual 240V secondaries are a dime a dozen.
the edcor outputs are 6600 plate to plate. as for the 365v, i'd put that on the schematic because it was the voltage that i foresaw myself having when i was using ss rectification and a clc filter.
i do quite like the idea of using an industrial 240-0-240 transformer, or maybe a 240-240. would it be possible to get 880V centertapped instead? is there a difference? the problem is, i don't really know where i could look to find such a transformer. the only places i know to get transformers are audio hobbyist/diy places.
i do quite like the idea of using an industrial 240-0-240 transformer, or maybe a 240-240. would it be possible to get 880V centertapped instead? is there a difference? the problem is, i don't really know where i could look to find such a transformer. the only places i know to get transformers are audio hobbyist/diy places.
The two secondaries on the industrial PT can be tied together for 240-0-240, some Ive bought came that way. Ive bought several of them from ebay at as little as $10/KVA (plus more than that again in shipping). Id use a Graetz (hybrid tube) bridge before series connecting multiple PTs.
Is your heart set on vacuum rectification?
Is your heart set on vacuum rectification?
Search Ebay for :
industrial transformer
industrial control transformer
control transformer
Popular brands are GE, Square D, Hammond and others
You want one that has two 240 volt windings (often labled primary) and two 120 volt windings. They come in other flavors that are not really suited for tube amps. New they are expensive, on Ebay they are often cheap. They come in power ratings from 50VA to several KVA. For your amp one from 300VA to 1 KVA will do fine, although the 1KVA transformer is big and heavy. I use the 500VA transformers for tube amps. I think you may have trouble getting 400 volts DC from one of these though. With both windings in series and a bridge rectifier, I get over 600 Volts DC from one of them. It powers a sweep tube amp that puts out 140 watts per channel. With a conventional full wave with the center tap grounded I get about 310 volts. You might be able to use a bridge rectifier and a choke input filter but I think that you will get too much voltage.
industrial transformer
industrial control transformer
control transformer
Popular brands are GE, Square D, Hammond and others
You want one that has two 240 volt windings (often labled primary) and two 120 volt windings. They come in other flavors that are not really suited for tube amps. New they are expensive, on Ebay they are often cheap. They come in power ratings from 50VA to several KVA. For your amp one from 300VA to 1 KVA will do fine, although the 1KVA transformer is big and heavy. I use the 500VA transformers for tube amps. I think you may have trouble getting 400 volts DC from one of these though. With both windings in series and a bridge rectifier, I get over 600 Volts DC from one of them. It powers a sweep tube amp that puts out 140 watts per channel. With a conventional full wave with the center tap grounded I get about 310 volts. You might be able to use a bridge rectifier and a choke input filter but I think that you will get too much voltage.
First of all, what do you mean by a Graetz bridge? I'll wiki it after this. With a regular full-wave bridge from a 5AR4, I'm simulating 420V, and with a 6AU4GT, it's more like 415. I'd rather be a bit above the voltage than down at around 360V with a 279X (425V secondary).Tweeker [/i][b] Is your heart set on vacuum rectification? [/B][/QUOTE] Increasingly so. Although it's not the most efficient said:
I still have nowhere near enough cash at the moment to finish this, so I'll keep my options open for a bit. I'm still awaiting a response from Edcor about getting some custom-wound 450V's, and given a reasonable price, I'd definitely take that route. I've heard good things about people successfully getting custom winding jobs from Edcor for reasonable prices, so I'm confident that this will be the best way.
edit: realized that a graetz bridge is a full-wave diode bridge. under "full wave" in PSUDII I get a drop to 405V or so with a 480V 4% regulation transformer.
A graetz bridge is a bridge rectifier made with two solid state diodes and two rectifier tubes. The tubes can be in the same envelope (a 5AR4) or two seperate tubes (6AU4's). The advantages are the soft start and smoothness of tubes, but only one filament winding (instead of 3) and less voltage drop than 4 tube diodes.
I believe that, strictly speaking, a Graetz bridge is ANY bridge rectifier. What you're talking about is called a hybrid Graetz bridge . . . but who cares? A rose by any other name, etc.
I understand that putting vacuum tube diodes together with SS diodes in that way has the desired effect of eliminating the SS hash, in addition to the other advantages you mentioned. I particularly like TV damper tubes in this configuration, because of their quite long warm-up time and low voltage drop. They do use a lot of heater current but they have the advantage of very high heater-to-cathode voltage tolerance, which means that you could share their heater supply with other tubes if you needed to. And they are rugged!
I understand that putting vacuum tube diodes together with SS diodes in that way has the desired effect of eliminating the SS hash, in addition to the other advantages you mentioned. I particularly like TV damper tubes in this configuration, because of their quite long warm-up time and low voltage drop. They do use a lot of heater current but they have the advantage of very high heater-to-cathode voltage tolerance, which means that you could share their heater supply with other tubes if you needed to. And they are rugged!
Hmm. I'm constantly simulating power supplies BUT there's one thing I'm wondering about. Does a large surge in the beginning of, say, .6A through a .2A-rated choke mean trouble? It seems like any time I tack large capacitances after a choke, the surge at the beginning begins to skyrocket. I sure hope that that surge wouldn't blow a choke, because if it does, it means using lots less capacitance, higher-rated chokes, and more of them I can still bring hum down by using 2 chokes, but that "reservoir of power" to help with possible load peaks kind of fizzles out to maybe two 50uF caps instead of the mighty 500...
I can still bring hum down by using 2 chokes, but that "reservoir of power" to help with possible load peaks kind of fizzles out to maybe two 50uF caps instead of the mighty 500...
With a choke of decent quality this should not be a problem, it is harder on the rectifier tube than anything else. My latest amp has the big Antek transformer (currently, I keep changing them, it is atill a breadboard) a 5AR4 or SS diodes - switchable, a 47 uF cap, a choke, and a combination of caps that total 320 uF. I have been swapping chokes through this amp also including all of the cheap ($6 and $15) chokes from Allied. No issues so far despite purposeful abuse to verify a bulletproof design. I have never had a choke fail if it was rated for enough current.
I tried some surplus chokes of unknown current ratings which got far too hot and eventually started smoking, but none failed on turn on. I later found that they were rated for 70 mA and I was drawing 150 through them. Hey they were free.
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