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#1
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Coil Dope
I read that old 78 LP's broken into pieces & mixed with a particular solvent
was used as coil dope. Does anybody remember which solvent was used & how affective it was? |
#2
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Coil Dope
On Mon, 09 Feb 2009 16:47:15 GMT, "Spin"
wrote: I read that old 78 LP's broken into pieces & mixed with a particular solvent was used as coil dope. Does anybody remember which solvent was used & how affective it was? Coil dope can be made from polystyrene packing peanuts dissolved in acetone. Q-Dope is some kind of cellulose polymer broken down in the same solvents. If you're planning on making your own, it does take several days and plenty of agitation to produce a suitable sticky mess. The very old 78 rpm records were originally made from Bakelite, which is quite resistant to chlorinated hydrocarbon solvents. During WWII, Vinyl records appeared as a substitute for Bakelite. It's easy to tell the difference. Bakelite is thermosetting plastic and is unaffected by acetone. Vinyl is thermoplastic and is softened by acetone. My guess is that whomever suggested dissolving records wanted to trick you into breaking your 78 rpm records. (Note: I'm sloooooly transcribbling my record collection to various digital formats). You don't state what you're trying to accomplish. If it's cleaning the Q-Dope off old coils, acetone softens it nicely. Wipe clean and you're done. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
#3
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Coil Dope
I read that old 78 LP's broken into pieces & mixed with a particular solvent
was used as coil dope. Does anybody remember which solvent was used & how affective it was? 78s were often made of shellac, and the usual solvent for shellac is denatured alcohol. I believe that some other 78s were made from cellulose acetate... for this material I believe that acetone would be a usable solvent. My understanding is that commercial Q-dope uses polystyrene, dissolved in a suitable solvent. According to an article by Barry Ornitz WA4VQZ (the text is at http://yarchive.net/electr/coil_dope.html), a very acceptable coil dope can be home-brewed by dissolving ordinary polystyrene "packing peanuts" in either toluene or acetone (the latter is less toxic). -- Dave Platt AE6EO Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior I do _not_ wish to receive unsolicited commercial email, and I will boycott any company which has the gall to send me such ads! |
#4
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Coil Dope
Jeff Liebermann wrote:
Coil dope can be made from polystyrene packing peanuts dissolved in acetone. Beware; this produces significant quantities of styrene monomer, a known carcinogen. |
#5
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Coil Dope
Clifford Heath wrote:
Jeff Liebermann wrote: Coil dope can be made from polystyrene packing peanuts dissolved in acetone. Beware; this produces significant quantities of styrene monomer, a known carcinogen. only in Canadian rats |
#6
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Coil Dope
On Tue, 10 Feb 2009 10:09:17 +1100, Clifford Heath
wrote: Jeff Liebermann wrote: Coil dope can be made from polystyrene packing peanuts dissolved in acetone. Beware; this produces significant quantities of styrene monomer, a known carcinogen. That seems to be debatable: http://www.styrenemonomer.org/3.5.html Of course, that comes from the Styrene Products Association, which might be slightly biased. -- # Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060 # 831-336-2558 # http://802.11junk.com # http://www.LearnByDestroying.com AE6KS |
#7
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Coil Dope
"Dave Platt" wrote in message
... I read that old 78 LP's broken into pieces & mixed with a particular solvent was used as coil dope. Does anybody remember which solvent was used & how affective it was? 78s were often made of shellac, and the usual solvent for shellac is denatured alcohol. I believe that some other 78s were made from cellulose acetate... for this material I believe that acetone would be a usable solvent. My understanding is that commercial Q-dope uses polystyrene, dissolved in a suitable solvent. Toluene. According to an article by Barry Ornitz WA4VQZ (the text is at http://yarchive.net/electr/coil_dope.html), a very acceptable coil dope can be home-brewed by dissolving ordinary polystyrene "packing peanuts" in either toluene or acetone (the latter is less toxic). Thanks for mentioning this archive Dave. I strongly suggest that before anyone tries making their own Q-dope, they read ALL the safety information given there. And yes it really does take several weeks for the "cotton balls" to fully dissolve. What I think that "Spin" was referring to was that early pressings were made from cellulose acetate. Acetone would be the solvent of choice here. I was not aware that phenol formaldehyde thermoset resins were ever used for records, but if you find any, they won't dissolve in anything! As for the worry that when Styrofoam is dissolved in a solvent, styrene is released - forget about it. Styrene is rather volatile and has a VERY distinctive odor. You would smell it if more than a trace amount were left in the peanuts. Polystyrene does not depolymerize by dissolving it in a solvent. Devcon's Duco Cement is nitrocellulose dissolved in acetone with a little camphor as a plasticizer and with small amounts of isopropanol and 1-methoxy-2-propanol acetate thrown in for good measure. If you only need a few ounces of Q-dope, Duco Cement is a suitable substitute. Roy Lewallen, W7EL, dipped a number of coils in various materials (RTV silicone, epoxy cement, Q-dope, hot melt adhesive, etc.) a while back and then measured their losses with a Q-meter. If Roy can find his old article, perhaps he can post it again. -- 73, Dr. Barry L. Ornitz WA4VZQ [transpose digits to reply] |
#8
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Coil Dope
Dr. Barry L. Ornitz wrote:
. . . Roy Lewallen, W7EL, dipped a number of coils in various materials (RTV silicone, epoxy cement, Q-dope, hot melt adhesive, etc.) a while back and then measured their losses with a Q-meter. If Roy can find his old article, perhaps he can post it again. Great memory, Barry! It was posted on Dec. 16, 1998. A copy of the original posting follows. I didn't do any other experiments as I said I would, and I've gotten very little confirming or contradictory feedback. I recall you and some other folks posting some very good information about RTV, the general thrust of which was that there's a very wide range of formulations, so results might vary a lot from what I measured. --------------- Spurred by recent comments and questions on this newsgroup, I made some inductors last weekend and measured them. Results follow. Toroidal Inductor Measurements Roy Lewallen, W7EL December, 1998 Test Equipment Inductance: GR 1606-A impedance meter. Stray series impedance was removed by initial calibration. Stray shunt capacitance was separately measured and removed mathematically. Repeatability is within about +/- 2%. No attempt was made to establish accuracy. Q: A home-made fixture was used. This is simply an air-variable capacitor which the inductor is connected across. Coupling into and out of the fixture with signal generator and oscilloscope is done with very small capacitors. The Q is calculated from the center frequency and 3 dB bandwidth. Use of frequency counter, built-in oscilloscope voltmeter, and switchable 3 dB pad allow repeatability of about +/- 2%. Checks against a commercial Q meter show agreement within a few percent. All measurements were made at 10 MHz. Experiment 1: Coatings Several identical inductors were fabricated, then coated with various compounds. Inductance and Q were measured before and after coating. The inductors were wound on Micrometals T-50-6 cores (Carbonyl SF material, relative permeability 8.5) with 25 turns of #22 wire. This just fits on a single layer. Ind. # Uncoated Coated Coating L(uH) Q L(uH) Q 1 2.54 281 2.54 284 None (control) 2 2.52 286 2.54 218 Duco cement 3 2.51 267 2.52 265 Standard RTV 4 2.52 280 5 2.54 279 2.55 255 Clear hot melt glue 6 2.48 268 2.55 164 "Sealing tape" 7 2.51 283 2.51 262 Paraffin 8 2.55 262 9 2.56 281 2.59 278 GE Silicone II 10 2.50 283 11 2.51 277 Notes (by inductor number): Unless otherwise noted, coatings covered the entire core and winding, extending more than a wire diameter beyond the outside of the wire, and the center of the core was filled. Inductances within about 0.3 uH and Q's within less than about 5 should be considered equal. 1. Inductor Q was measured several times over several days to establish repeatability. Results were 280, 281, 283, 286, 284. (The apparent trend is interesting, but not conclusive.) 2. Devcon Duco(R) Cement, allowed to dry for 24 hours. Although a generous coating was applied, the dried coating was less than a wire diameter in thickness, and the center of the core wasn't filled. 3. Dap Dow Corning 100% Silicone Sealant, Clear, allowed to cure for 24 hours. This is standard acetic-acid (vinegar) curing RTV. 5. Stanley All Purpose GlueSticks, claimed set time 25-30 seconds. These are nearly clear, translucent white, and not tan or brown colored. 6. This was some stuff I got surplus. It's a black, sticky, rubbery compound something like Coax Seal, but may be of entirely different composition. It's in the form of a thick tape. It's soluble in naphtha (and the solution dyes everything black it gets on), but acetone doesn't touch it. 7. Household canning paraffin. (I don't know what it's called in Britain, but I'm not referring to the liquid -- kerosene to us -- you call paraffin. This is a common wax made from petroleum.) 9. GE Silicone II Household Glue & Seal, Clear. This is a non-acetic-acid curing RTV. Allowed to cure for two days. Still just a little soft even after this much curing. 11. This is the same core as #6. After the coated #6 was measured, the core was cleaned, the winding cut off, the core further cleaned, then a new winding put on. Comments: I had made some measurements years ago, but couldn't locate the results. I recall that standard RTV was poor (lowered Q noticeably) but that an industrial non-acetic-acid curing RTV was good. The results with standard RTV in this test were striking. Either a) the formulation of standard RTV has changed over the years, b) there are major differences among brands, or c) my memory is faulty. I recall from my earlier tests that epoxy was quite poor, but this has to be qualified after the experience with RTV. There's a huge number of different types of epoxy, and some may be much worse than others. I might test some in the future, but didn't during this test. I intend to test Q-dope in the future, but didn't have any on hand. Conclusions: Of the materials tested, both types of RTV stand out as having a negligible effect on inductor Q. Hot melt glue and paraffin have a small enough effect that they should be tolerable for many applications. Duco cement seriously degrades Q, even in a much thinner layer than the other coatings. The "sealing tape", tested out of curiosity, shows just how great a degradation can be caused by a poor coating. None of the coatings made much of a change in apparent inductance. This implies that the reduction in Q is due primarily to dielectric loss rather than simple increase in capacitance due to the material's dielectric constant. Note the difference in inductance and Q between inductors 6 and 11, which were wound on the same core. Apparently physical differences in the windings (perhaps such as tightness and conformance to the core, or uniformity of turn spacing) are a major contributor to differences between inductors. All the cores used in the test were ordered at the same time, so they may have come from the same batch and have relatively little variation. On the basis of just the comparison between numbers 6 and 11, it's entirely possible that most of the variation between inductors in this experiment is due to winding differences. The variation might be less if smaller wire with less stiffness is used. Experiment 2: Turn Spacing I believe it's well established that even a partial second layer can greatly reduce the Q of a toroidal inductor. But I had recently heard that optimum Q is achieved when the first layer isn't quite full, but rather has about a 30 degree gap in the winding, to reduce the capacitance between winding ends. To test this, I wound 23 turns of #22 wire on a T-50-6 core, and measured the Q with the turns pushed close together to make a gap (of about 30 degrees), and then spread to evenly distribute the turns completely around the core. Measured 10 MHz Q's were 272 and 284, respectively. (Inductances were 2.21 and 2.11 uH.) This one test doesn't by any means exhaust all the possibilities of core geometries, permeabilities, number of turns, and wire size, all of which may play a role. But if there's any advantage to leaving a gap, I believe it would be a small one. And in at least one case, it's slightly better not to. Another test was run using 10 turns of the same size wire on the same core. With the turns pushed together (the winding covering less than half the core), Q was 213, L was 841 nH. With the turns spread evenly around the core, Q was 209 but the L had dropped to 505 nH. I reasoned that a more fair comparison would be with a winding of about the same inductance as the original close-spaced one. This required 15 turns when distributed around the core, and resulted in a Q of 257 and L of 924 uH. Here again, the Q is best when the turns are evenly distributed. Note that type 6 powdered iron has a very low relative permeability (8.5), so results might be different with higher-permeability materials. However, this is the material I usually use for high-Q inductors at HF, so I'm most interested in how it's affected. Experiment 3: "Regressive" Winding In the past, I've found what I thought was a moderate improvement in Q by "regressively" winding an inductor. To do this, you wind half the turns in the normal manner. Then you pass the wire through the hole, but to the opposite side of the inductor (with it ending up beside the first turn), then completing the winding from the vicinity of the first turn back toward the origination of the crossover. The result is an inductor with the two leads coming from points directly opposite each other. Stray capacitance is allegedly reduced by keeping the ends of the winding apart. An inductor wound in this manner with 25 turns of #22 wire measured Q = 285, L = 2.48 uH. This Q is on the high side, and the L on the low side, of the uncoated inductors measured in Experiment 1. I didn't try comparing with a standard winding on the same core, since the same number of turns wound on the same core at different times (e.g., inductors 6 and 11 in Experiment 1) were shown to come out differently from each other. My conclusion is that any Q improvement due to "regressive" winding is slight. Another claim for "regressive" winding is that it eliminates the "single turn" effect of toroidal inductors. A normal toroid will couple into its surroundings as though it consists of a single turn the size of the core. In the "regressively" wound inductor, there are two half-turns in opposite directions, so coupling should be reduced. I haven't tested this in any way, but it may be an argument in favor of the method. The relatively long wire of the crossover turn would contribute to coupling, however. I'll undertake more experiments and measurements as time permits. I'd love to hear from anyone who has made either supporting or contradictory quantitative measurements. Roy Lewallen, W7EL |
#9
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Coil Dope
"Roy Lewallen" wrote in message treetonline... Dr. Barry L. Ornitz wrote: . . . Roy Lewallen, W7EL, dipped a number of coils in various materials (RTV silicone, epoxy cement, Q-dope, hot melt adhesive, etc.) a while back and then measured their losses with a Q-meter. If Roy can find his old article, perhaps he can post it again. Great memory, Barry! It was posted on Dec. 16, 1998. A copy of the original posting follows. I didn't do any other experiments as I said I would, and I've gotten very little confirming or contradictory feedback. I recall you and some other folks posting some very good information about RTV, the general thrust of which was that there's a very wide range of formulations, so results might vary a lot from what I measured. --------------- Spurred by recent comments and questions on this newsgroup, I made some inductors last weekend and measured them. Results follow. Toroidal Inductor Measurements Roy Lewallen, W7EL December, 1998 Test Equipment Inductance: GR 1606-A impedance meter. Stray series impedance was removed by initial calibration. Stray shunt capacitance was separately measured and removed mathematically. Repeatability is within about +/- 2%. No attempt was made to establish accuracy. Q: A home-made fixture was used. This is simply an air-variable capacitor which the inductor is connected across. Coupling into and out of the fixture with signal generator and oscilloscope is done with very small capacitors. The Q is calculated from the center frequency and 3 dB bandwidth. Use of frequency counter, built-in oscilloscope voltmeter, and switchable 3 dB pad allow repeatability of about +/- 2%. Checks against a commercial Q meter show agreement within a few percent. All measurements were made at 10 MHz. Experiment 1: Coatings Several identical inductors were fabricated, then coated with various compounds. Inductance and Q were measured before and after coating. The inductors were wound on Micrometals T-50-6 cores (Carbonyl SF material, relative permeability 8.5) with 25 turns of #22 wire. This just fits on a single layer. Ind. # Uncoated Coated Coating L(uH) Q L(uH) Q 1 2.54 281 2.54 284 None (control) 2 2.52 286 2.54 218 Duco cement 3 2.51 267 2.52 265 Standard RTV 4 2.52 280 5 2.54 279 2.55 255 Clear hot melt glue 6 2.48 268 2.55 164 "Sealing tape" 7 2.51 283 2.51 262 Paraffin 8 2.55 262 9 2.56 281 2.59 278 GE Silicone II 10 2.50 283 11 2.51 277 Notes (by inductor number): Unless otherwise noted, coatings covered the entire core and winding, extending more than a wire diameter beyond the outside of the wire, and the center of the core was filled. Inductances within about 0.3 uH and Q's within less than about 5 should be considered equal. 1. Inductor Q was measured several times over several days to establish repeatability. Results were 280, 281, 283, 286, 284. (The apparent trend is interesting, but not conclusive.) 2. Devcon Duco(R) Cement, allowed to dry for 24 hours. Although a generous coating was applied, the dried coating was less than a wire diameter in thickness, and the center of the core wasn't filled. 3. Dap Dow Corning 100% Silicone Sealant, Clear, allowed to cure for 24 hours. This is standard acetic-acid (vinegar) curing RTV. 5. Stanley All Purpose GlueSticks, claimed set time 25-30 seconds. These are nearly clear, translucent white, and not tan or brown colored. 6. This was some stuff I got surplus. It's a black, sticky, rubbery compound something like Coax Seal, but may be of entirely different composition. It's in the form of a thick tape. It's soluble in naphtha (and the solution dyes everything black it gets on), but acetone doesn't touch it. 7. Household canning paraffin. (I don't know what it's called in Britain, but I'm not referring to the liquid -- kerosene to us -- you call paraffin. This is a common wax made from petroleum.) 9. GE Silicone II Household Glue & Seal, Clear. This is a non-acetic-acid curing RTV. Allowed to cure for two days. Still just a little soft even after this much curing. 11. This is the same core as #6. After the coated #6 was measured, the core was cleaned, the winding cut off, the core further cleaned, then a new winding put on. Comments: I had made some measurements years ago, but couldn't locate the results. I recall that standard RTV was poor (lowered Q noticeably) but that an industrial non-acetic-acid curing RTV was good. The results with standard RTV in this test were striking. Either a) the formulation of standard RTV has changed over the years, b) there are major differences among brands, or c) my memory is faulty. I recall from my earlier tests that epoxy was quite poor, but this has to be qualified after the experience with RTV. There's a huge number of different types of epoxy, and some may be much worse than others. I might test some in the future, but didn't during this test. I intend to test Q-dope in the future, but didn't have any on hand. Conclusions: Of the materials tested, both types of RTV stand out as having a negligible effect on inductor Q. Hot melt glue and paraffin have a small enough effect that they should be tolerable for many applications. Duco cement seriously degrades Q, even in a much thinner layer than the other coatings. The "sealing tape", tested out of curiosity, shows just how great a degradation can be caused by a poor coating. None of the coatings made much of a change in apparent inductance. This implies that the reduction in Q is due primarily to dielectric loss rather than simple increase in capacitance due to the material's dielectric constant. Note the difference in inductance and Q between inductors 6 and 11, which were wound on the same core. Apparently physical differences in the windings (perhaps such as tightness and conformance to the core, or uniformity of turn spacing) are a major contributor to differences between inductors. All the cores used in the test were ordered at the same time, so they may have come from the same batch and have relatively little variation. On the basis of just the comparison between numbers 6 and 11, it's entirely possible that most of the variation between inductors in this experiment is due to winding differences. The variation might be less if smaller wire with less stiffness is used. Experiment 2: Turn Spacing I believe it's well established that even a partial second layer can greatly reduce the Q of a toroidal inductor. But I had recently heard that optimum Q is achieved when the first layer isn't quite full, but rather has about a 30 degree gap in the winding, to reduce the capacitance between winding ends. To test this, I wound 23 turns of #22 wire on a T-50-6 core, and measured the Q with the turns pushed close together to make a gap (of about 30 degrees), and then spread to evenly distribute the turns completely around the core. Measured 10 MHz Q's were 272 and 284, respectively. (Inductances were 2.21 and 2.11 uH.) This one test doesn't by any means exhaust all the possibilities of core geometries, permeabilities, number of turns, and wire size, all of which may play a role. But if there's any advantage to leaving a gap, I believe it would be a small one. And in at least one case, it's slightly better not to. Another test was run using 10 turns of the same size wire on the same core. With the turns pushed together (the winding covering less than half the core), Q was 213, L was 841 nH. With the turns spread evenly around the core, Q was 209 but the L had dropped to 505 nH. I reasoned that a more fair comparison would be with a winding of about the same inductance as the original close-spaced one. This required 15 turns when distributed around the core, and resulted in a Q of 257 and L of 924 uH. Here again, the Q is best when the turns are evenly distributed. Note that type 6 powdered iron has a very low relative permeability (8.5), so results might be different with higher-permeability materials. However, this is the material I usually use for high-Q inductors at HF, so I'm most interested in how it's affected. Experiment 3: "Regressive" Winding In the past, I've found what I thought was a moderate improvement in Q by "regressively" winding an inductor. To do this, you wind half the turns in the normal manner. Then you pass the wire through the hole, but to the opposite side of the inductor (with it ending up beside the first turn), then completing the winding from the vicinity of the first turn back toward the origination of the crossover. The result is an inductor with the two leads coming from points directly opposite each other. Stray capacitance is allegedly reduced by keeping the ends of the winding apart. An inductor wound in this manner with 25 turns of #22 wire measured Q = 285, L = 2.48 uH. This Q is on the high side, and the L on the low side, of the uncoated inductors measured in Experiment 1. I didn't try comparing with a standard winding on the same core, since the same number of turns wound on the same core at different times (e.g., inductors 6 and 11 in Experiment 1) were shown to come out differently from each other. My conclusion is that any Q improvement due to "regressive" winding is slight. Another claim for "regressive" winding is that it eliminates the "single turn" effect of toroidal inductors. A normal toroid will couple into its surroundings as though it consists of a single turn the size of the core. In the "regressively" wound inductor, there are two half-turns in opposite directions, so coupling should be reduced. I haven't tested this in any way, but it may be an argument in favor of the method. The relatively long wire of the crossover turn would contribute to coupling, however. I'll undertake more experiments and measurements as time permits. I'd love to hear from anyone who has made either supporting or contradictory quantitative measurements. Roy Lewallen, W7EL I seem to recall reading that Styrene had the best dielectric properties of the plastics. I did some similar experiments building 1/4 wave spikes in a BNC connector for 2m HTs and found that glues would heat up from the RF. Clear epoxy worked best and JB weld, Pipe dope, Silicone sealers and Hot glue were poor performers. I still have some fiberglass tape that I use for torroids. |
#10
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Coil Dope
Jim Higgins wrote:
On Tue, 10 Feb 2009 10:09:17 +1100, Clifford Heath Beware; this produces significant quantities of styrene monomer, a known carcinogen. No it doesn't. It's purely a dissolution process with no chemical reaction. Glad to hear it - I forget who scared me off using a batch I made and held on to, unable to decide how to even dispose of it. |
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