I've been heavy into SE tube amps for the past year or two, and am edging slowly into push-pull territory. Inspired by Tubelab's torture of 6BQ6s with shockingly high output power, I have in mind an amp I'll call "Killer". It will feature screen driven 25LR6 output tubes. I'm looking for around 100W per channel, if not steady RMS, at least for an extended burst. The most important part will be the output iron. .I don't want to spend a fortune, so I'm initially looking at budget options. Option one is using one of the E-I based transformers with 5k primary impedance. Classic examples are made by both Hammond and Edcor. Option two is using a toroidal output transformer. This is where screen driven push-pull amps may especialy shine, as they operate well with low levels of bias current, making it much safer to use toroidal output transformers. Antek has just released a series of push-pull toroidal transformers that appear to ape the Plitron offerings at about 1/3 the price. The high frequency response is inferior to the Plitrons, perhaps implying less interleaving/more leakage.. Does anyone have any comments (based on experience) for usin g these transformers in a 100W amp? Any other suggestions for powerful iron that won't require me to take out a second mortgage?
I don't need to go all that cheap. By the same token, I don't want to be paying $300 per transformer, either. That (I guess) describes my zone of comfort . Yeah, Stew, bass is important - so are the highs, but if they get to be a problem, I'll have a slew of little SE amps with crystalline highs waiting in the wings to do tweeter duty in a biamp rig. This is an exercise in raw Neanderthal (well, maybe Cro-Magnon) power.
I did some back of the envelope calculations this afternoon. Information regarding the 6LR6 is rather thin on the ground (I've got a few numbers in my old, tattered RCA handbook, but no curves anywhere). The guts and ratings look very similar to the well-characterized 6JE6/6LQ6. First assumption - the tube will pull to within 50V of ground at peak excursions. The 5k transformers (1.25k/side, really) have a 12.5:1 turns ratio into an 8 ohm load. Assuming no other losses, if you use a 550V plate supply and pull down to 50V, you get 40V peak at the output. This is 5A peak into an 8 ohm load. Reflecting bacwards, it's 400 mA peak plate current. This is well within the peak rating of the 6JE6 and 6LR6 and ok with the average cathode current, too. This would disappoint George (no red plate? - darn...). More importantlly, with somewhere between 75-100V on G2, a 6LQ6 will pull down to 50V, 400 mA. This gives me great expectations for the similarly sized 6LR6. Putting it all together, with a 5k transformer and 550V plate supply, I get about a 98W RMS output capability into an 8 ohm load. Losses will eat some of this, but I can always bump up the plate supply a bit to compensate. I'm going to use a switching power supply, so I'll have a lot of freedom in terms of what voltages I can deliver.
The 100W Edcor iron is less than $100 each. The Hammonds are about $20 more expensive, and are no doubt huge (but ugly (butt ugly?)) clunkers with good bass, The Anteks are about the same price as the Hammonds, but with different impedance. Are there any other transformer candidates out there that aren't priced out in cloud la-la land?
I did some back of the envelope calculations this afternoon. Information regarding the 6LR6 is rather thin on the ground (I've got a few numbers in my old, tattered RCA handbook, but no curves anywhere). The guts and ratings look very similar to the well-characterized 6JE6/6LQ6. First assumption - the tube will pull to within 50V of ground at peak excursions. The 5k transformers (1.25k/side, really) have a 12.5:1 turns ratio into an 8 ohm load. Assuming no other losses, if you use a 550V plate supply and pull down to 50V, you get 40V peak at the output. This is 5A peak into an 8 ohm load. Reflecting bacwards, it's 400 mA peak plate current. This is well within the peak rating of the 6JE6 and 6LR6 and ok with the average cathode current, too. This would disappoint George (no red plate? - darn...). More importantlly, with somewhere between 75-100V on G2, a 6LQ6 will pull down to 50V, 400 mA. This gives me great expectations for the similarly sized 6LR6. Putting it all together, with a 5k transformer and 550V plate supply, I get about a 98W RMS output capability into an 8 ohm load. Losses will eat some of this, but I can always bump up the plate supply a bit to compensate. I'm going to use a switching power supply, so I'll have a lot of freedom in terms of what voltages I can deliver.
The 100W Edcor iron is less than $100 each. The Hammonds are about $20 more expensive, and are no doubt huge (but ugly (butt ugly?)) clunkers with good bass, The Anteks are about the same price as the Hammonds, but with different impedance. Are there any other transformer candidates out there that aren't priced out in cloud la-la land?
The Antek OT data doesn't specify what driving impedance was used to derive the data curves. If a simple 50 Ohm generator was used, then the data are no better than random wound power toroids. Just that they may have used enough turns presumably for the required inductance, which they also don't list.
They need to post more info, like primary inductance, and distributed capacitance or resonance frequency, and use appropriate source impedances for deriving the freq. response curves.
Progressive wound units should have much better specs than those listed. It's also strange that the curves given suddenly improve with the lowest power unit, after consistently degrading with each drop to a lower power/ higher Z from the highest power unit.
I have given up on commercial toroid OTs, I am building a shuttleless toroid winder. With one of these, its easier to wind toroids than E-I s. Then I can do progressive winds, and any turns ratios I want. 500KHZ bandwidth typical.
Don
They need to post more info, like primary inductance, and distributed capacitance or resonance frequency, and use appropriate source impedances for deriving the freq. response curves.
Progressive wound units should have much better specs than those listed. It's also strange that the curves given suddenly improve with the lowest power unit, after consistently degrading with each drop to a lower power/ higher Z from the highest power unit.
I have given up on commercial toroid OTs, I am building a shuttleless toroid winder. With one of these, its easier to wind toroids than E-I s. Then I can do progressive winds, and any turns ratios I want. 500KHZ bandwidth typical.
Don
Lundahl LL1620 @ 6k would do it at $235/ea, on the higher end
Hashimoto has something suitable but shockingly expensive
James I think has something, but don't know how much it costs to import them now that euphonia is out.
I had Bud Purvine of Onetics made me some 100watt OPT's that were well under your threshold for pain.
Doug likes Heyboer, maybe they have something in that range.
Electra-print is probably worth looking into.
Hashimoto has something suitable but shockingly expensive
James I think has something, but don't know how much it costs to import them now that euphonia is out.
I had Bud Purvine of Onetics made me some 100watt OPT's that were well under your threshold for pain.
Doug likes Heyboer, maybe they have something in that range.
Electra-print is probably worth looking into.
http://freepatentfetcher.com/GetPatentPDF.php?f=Pats/US/41/27/US4127238.pdf
Hmmm, looks like that won't download it directly. It's patent # 4127238
Darned if I can get that dumb website to download it.
Try this one:
http://www.uspto.gov/
Hmmm, looks like that won't download it directly. It's patent # 4127238
Darned if I can get that dumb website to download it.
Try this one:
http://www.uspto.gov/
Found the problem, try this one:
http://free.patentfetcher.com/GetPat...7/US4127238.pdf
Geez, still doesn't work, at least not from this web page. Works for me if I copy it into the address line and hit GO --- if I'm already on that website. Maybe its some kind of protected or keyed access.
http://free.patentfetcher.com/GetPat...7/US4127238.pdf
Geez, still doesn't work, at least not from this web page. Works for me if I copy it into the address line and hit GO --- if I'm already on that website. Maybe its some kind of protected or keyed access.
If you know the Patent number, then the best site to use to view patents is --> www.pat2pdf.org
Here is the patent you were trying to link to --> http://www.pat2pdf.org/patents/pat4127238.pdf
Rgs, JLH
Here is the patent you were trying to link to --> http://www.pat2pdf.org/patents/pat4127238.pdf
Rgs, JLH
Nice find Don!
I printed the patent and tried to understand the working, but it is not completely clear for me, yet. Besides I have enough projects to finish for which I already have the needed iron
Still very interesting, my first application thought was to wind an autoformer type transformer volume control. The single winding should be the easiest to get right?!
Erik
I printed the patent and tried to understand the working, but it is not completely clear for me, yet. Besides I have enough projects to finish for which I already have the needed iron
Still very interesting, my first application thought was to wind an autoformer type transformer volume control. The single winding should be the easiest to get right?!
Erik
"The simple version is a bicycle rim."
You are going to have trouble getting the spokes thru the toroid. The shuttle type winders are the most complicated designs when you consider all the roller supports and gearing, and the least flexible or capable (they cannot handle a small winding window).
The Potthoff design doesn't use any shuttle. Only wire travels thru the toroid. Its easy to build too. Just three sheets of teflon, machined into a C shape and a timing belt running around it. Parts are on the way already.
Don
You are going to have trouble getting the spokes thru the toroid. The shuttle type winders are the most complicated designs when you consider all the roller supports and gearing, and the least flexible or capable (they cannot handle a small winding window).
The Potthoff design doesn't use any shuttle. Only wire travels thru the toroid. Its easy to build too. Just three sheets of teflon, machined into a C shape and a timing belt running around it. Parts are on the way already.
Don
Great ideas pop up in the most unusual threads. Thanks Don for uncovering this patent.
I've read it a number of times but fail to understand:
- How the wire is wound around the C-shaped belt loop & through the toroid at the same time? - I can see how a belt can rotate around in a c-shaped sausage driven by an inner cog but if the wire is threaded through the toroid & attached to the belt which is then turned how does a second & subsequent loop go through the toroid?
- Presuming all the loops needed are threaded through the toroid & around the C belt how are they then slipped off the belt individually in a controlled fashion?
I am keen to build one of these winders, maybe a separate thread could be started which would give this more exposure to the concept for the benefit of the community?
I've read it a number of times but fail to understand:
- How the wire is wound around the C-shaped belt loop & through the toroid at the same time? - I can see how a belt can rotate around in a c-shaped sausage driven by an inner cog but if the wire is threaded through the toroid & attached to the belt which is then turned how does a second & subsequent loop go through the toroid?
- Presuming all the loops needed are threaded through the toroid & around the C belt how are they then slipped off the belt individually in a controlled fashion?
I am keen to build one of these winders, maybe a separate thread could be started which would give this more exposure to the concept for the benefit of the community?
Moderator assistance request:
Looks like we should break out the toroid winder stuff as a separate thread if interest continues.
Jkeny:
"How the wire is wound around the C-shaped belt loop & through the toroid at the same time? ....."
As Kenpeter was attempting to explain, the easiest way is to look at it is as a shuttle type winder first. Imagine a hoop like shuttle or bobbin thru the core (bicycle rim). The wire is first spun onto the rim by spinning the rim and winding on wire (on the rim). Normally the wire start would be taped down to the rim.
Then the finishing end of the wire is attached to
the core holddown and the rim is slowly spun again. The wire winds around the core and pulls itself off one edge of the rim as needed. Ie, it spills over the edge of the rim by wire tension. Some friction effect is required to tension the wire and keep it held on the rim till needed too, this is often done by a C shaped spring leaf over the wire bundle on the rim.
Next, we conceptually replace the rim with the C shaped Teflon grooved, or slotted C, with a timing belt running around in its groove. (The initail wire windup procedure is modified so that one loop of wire is hand tightened around the C and thru the core and then twisted together in the core notchout of the C) The wire stays on the outside of the C, just like on the old rim, resting on the belt surface (but not the inner section of belt around the cog pulley). (the belt does its c-shaped sausage around the inner cog pulley simply for drive motion.)
The C stays stationary and remains outside the toroid. A notch (core notchout) in the C allows the toroid to rest around the pre-wound wire flow. The drive belt can be driven and the wire rotates around the C's loop thru the core. So the "shuttle or rim" is filled up initially with wire just like before. Then the wire end is tied down to the core holdown as before.
Now the winding procedure starts by running the belt drive again. The pre-wound wire bundle rotates around thru the core like before (just like with the rim, but now the effective rim is missing where the core notchout is) and the wire spills off the edge of the C for wire feed. The spill edge is rounded and of Teflon for easy feed. Instead of a spring tensioner, the patent design uses a teflon disk pressed up against the side of the C, forming a narrow gap (call it the slack accumulator) for the wire to pass thru.
During winding, the wire rotates around the C (on the belt surface) and thru the core, feeding wire off the C edge as needed. Obviously, when the current feed point recedes to the back of the C and then starts moving forward toward the core again, some excess wire occurs. This ends up forming a temporary loop in the slack accumulator until used up again by subsequent winding. The slack accumulator is a flat gap in the patent design, but a better approach might be a rounded spherical double surface so as to encourage the wire to form a round loop without sharp bends in the accumulator.
Looking at it from the side and following the spill off point: The wire wraps around the toroid until the spill point reaches the back of the C, then curves to form a loop in the accumulator as the spill off point moves forward again toward the core. Friction in the accumulator gap maintaining tension on the wire around the toroid even though there is excess wire spilled. Once the spill point passes thru the core again, the excess wire accumulator loop pulls smaller until it pulls down on the core thru the gap. Tension then pulls more wire off the spill point in the subsequent cycle until the spill point reaches the back side of the C again.
So from the core viewpoint, the wire mostly is pulling out of the accumulator gap for most of the cycle even when the spill off point passes thru the core. After the spill off point has passed thru and begins to recede from the core, the wire is pulled thru the core as the accumulator wire loop shrinks. The wire loop eventually pulls out of the inner edge of the gap and tightens around the core. Winding tension is determined by the friction in the accumulator gap, which is spring tensioned against the spill off side of the C.
So the accumulator gap provides close control of the wire winding position (on the toroid) during winding. Ideally it would have its notchout shaped to the contour of the core outer winding surface.
Whats nice here is the simplicity of construction with few moving parts and the lack of a shuttle or wheel rim passing thru the core. This gives the maximum room for wire to wind on the core. (you could even wind the core up to 100% fill if the wire length was adjusted just right, but this would not be a good idea for audio OTs. )
The shuttle type designs need elaborate rollers to keep the rim positioned during rotation (and not block spill off on the side) and to drive it. The rim itself must have provision for splitting to fit thru the toroid initially too. This makes a rough spot on the rim that spilloff wire has to pass over repeatedly. Different size rims may also be required for small and large toroids.
For both designs, the control of friction for side feed and wire tensioning is crucial. Significantly different wire sizes for primary and secondary require adjustability of this tensioning too. So this friction control is the achilles heel or greatest risk to limited DIY design efforts.
Don
Looks like we should break out the toroid winder stuff as a separate thread if interest continues.
Jkeny:
"How the wire is wound around the C-shaped belt loop & through the toroid at the same time? ....."
As Kenpeter was attempting to explain, the easiest way is to look at it is as a shuttle type winder first. Imagine a hoop like shuttle or bobbin thru the core (bicycle rim). The wire is first spun onto the rim by spinning the rim and winding on wire (on the rim). Normally the wire start would be taped down to the rim.
Then the finishing end of the wire is attached to
the core holddown and the rim is slowly spun again. The wire winds around the core and pulls itself off one edge of the rim as needed. Ie, it spills over the edge of the rim by wire tension. Some friction effect is required to tension the wire and keep it held on the rim till needed too, this is often done by a C shaped spring leaf over the wire bundle on the rim.
Next, we conceptually replace the rim with the C shaped Teflon grooved, or slotted C, with a timing belt running around in its groove. (The initail wire windup procedure is modified so that one loop of wire is hand tightened around the C and thru the core and then twisted together in the core notchout of the C) The wire stays on the outside of the C, just like on the old rim, resting on the belt surface (but not the inner section of belt around the cog pulley). (the belt does its c-shaped sausage around the inner cog pulley simply for drive motion.)
The C stays stationary and remains outside the toroid. A notch (core notchout) in the C allows the toroid to rest around the pre-wound wire flow. The drive belt can be driven and the wire rotates around the C's loop thru the core. So the "shuttle or rim" is filled up initially with wire just like before. Then the wire end is tied down to the core holdown as before.
Now the winding procedure starts by running the belt drive again. The pre-wound wire bundle rotates around thru the core like before (just like with the rim, but now the effective rim is missing where the core notchout is) and the wire spills off the edge of the C for wire feed. The spill edge is rounded and of Teflon for easy feed. Instead of a spring tensioner, the patent design uses a teflon disk pressed up against the side of the C, forming a narrow gap (call it the slack accumulator) for the wire to pass thru.
During winding, the wire rotates around the C (on the belt surface) and thru the core, feeding wire off the C edge as needed. Obviously, when the current feed point recedes to the back of the C and then starts moving forward toward the core again, some excess wire occurs. This ends up forming a temporary loop in the slack accumulator until used up again by subsequent winding. The slack accumulator is a flat gap in the patent design, but a better approach might be a rounded spherical double surface so as to encourage the wire to form a round loop without sharp bends in the accumulator.
Looking at it from the side and following the spill off point: The wire wraps around the toroid until the spill point reaches the back of the C, then curves to form a loop in the accumulator as the spill off point moves forward again toward the core. Friction in the accumulator gap maintaining tension on the wire around the toroid even though there is excess wire spilled. Once the spill point passes thru the core again, the excess wire accumulator loop pulls smaller until it pulls down on the core thru the gap. Tension then pulls more wire off the spill point in the subsequent cycle until the spill point reaches the back side of the C again.
So from the core viewpoint, the wire mostly is pulling out of the accumulator gap for most of the cycle even when the spill off point passes thru the core. After the spill off point has passed thru and begins to recede from the core, the wire is pulled thru the core as the accumulator wire loop shrinks. The wire loop eventually pulls out of the inner edge of the gap and tightens around the core. Winding tension is determined by the friction in the accumulator gap, which is spring tensioned against the spill off side of the C.
So the accumulator gap provides close control of the wire winding position (on the toroid) during winding. Ideally it would have its notchout shaped to the contour of the core outer winding surface.
Whats nice here is the simplicity of construction with few moving parts and the lack of a shuttle or wheel rim passing thru the core. This gives the maximum room for wire to wind on the core. (you could even wind the core up to 100% fill if the wire length was adjusted just right, but this would not be a good idea for audio OTs. )
The shuttle type designs need elaborate rollers to keep the rim positioned during rotation (and not block spill off on the side) and to drive it. The rim itself must have provision for splitting to fit thru the toroid initially too. This makes a rough spot on the rim that spilloff wire has to pass over repeatedly. Different size rims may also be required for small and large toroids.
For both designs, the control of friction for side feed and wire tensioning is crucial. Significantly different wire sizes for primary and secondary require adjustability of this tensioning too. So this friction control is the achilles heel or greatest risk to limited DIY design efforts.
Don
Thanks Don, for the comprehensive explanation - I think I have the idea now even though my spatial imagination is not as good as I'd like. I'll have to build a quick mock-up to picture how the wire will spool off the rim without tangling up - I'm sure your explanation of a spherical guide will stop the sharp bends.
Anyway, once built this would be a boon to this dIY hobby as I presume it could also be used in reverse to unwind cheap PS toroids & reuse cores. A great saving and a wonderful experimenters tool also - bifilar, progressive windings, etc.
Please keep us informed of your progress with this and your approach to progressive winding that seems to hold much promise for wide bandwith trafos.
Yes, please moderators a separate thread please if interest warrants
Edit: Just after posting, a thought occurred: Kenpeter's idea could work without cutting out a section of the rim - just pull the toroid core away from the rim with springs, i.e no need for the C-shaped belt at all? Am I right/wrong?
Anyway, once built this would be a boon to this dIY hobby as I presume it could also be used in reverse to unwind cheap PS toroids & reuse cores. A great saving and a wonderful experimenters tool also - bifilar, progressive windings, etc.
Please keep us informed of your progress with this and your approach to progressive winding that seems to hold much promise for wide bandwith trafos.
Yes, please moderators a separate thread please if interest warrants
Edit: Just after posting, a thought occurred: Kenpeter's idea could work without cutting out a section of the rim - just pull the toroid core away from the rim with springs, i.e no need for the C-shaped belt at all? Am I right/wrong?
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