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  • skyline1 commented on crispndry's instructable Easy amplifier8 months ago
    Easy amplifier

    Or shielded twisted pair with the braid connected at one end only

    Yes twisted pairs are only really effective with differential (Balanced) signals where the interference (common mode) signal is the same in both wires and cancels itself out

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  • How To Make The Mini Metal Foundry

    It could do just that If you blow too much air in or soften it like a blacksmiths forge

    I have built a small foundry myself (which we were actually using commercially) and I agree with all your comments. Charcoal will indeed reach a very high temperature indeed with sufficient air supplied.Not only "well above the melting point of hobbyists" (that made me laugh too) but above the melting point of the Silica Sand used in the furnace lining turning it into impure glass.The stuff I used was an Alumina based cement made by Purimachos Ltd in Bristol U.K. They make a whole range of refractory products and seem quite happy to deal with small volume orders from hobbyists.It is somewhat more expensive than plain silica sand and plaster of paris but not ridiculously so and will withstand any temperature most hobbyists will get to without degrading being used for industrial...see more »I have built a small foundry myself (which we were actually using commercially) and I agree with all your comments. Charcoal will indeed reach a very high temperature indeed with sufficient air supplied.Not only "well above the melting point of hobbyists" (that made me laugh too) but above the melting point of the Silica Sand used in the furnace lining turning it into impure glass.The stuff I used was an Alumina based cement made by Purimachos Ltd in Bristol U.K. They make a whole range of refractory products and seem quite happy to deal with small volume orders from hobbyists.It is somewhat more expensive than plain silica sand and plaster of paris but not ridiculously so and will withstand any temperature most hobbyists will get to without degrading being used for industrial steelmaking among other things.An air blast charcoal furnace can get hot enough to actually melt steel, indeed charcoal was used for smelting iron before Abraham Darby started using coke. I have tried it as an experiment and actually made a small quantity of usable cast iron.So be careful about how much air you blow in or you might actually melt your "Crucible" as some people have found out. The "pros" use Clay/Graphite or Silicon Carbide crucibles but they are really expensive nowadays (If you can get them at all) and even these will erode if you are casting iron.By the same publishers as the Dave Gingery books are a couple by Terry Aspin, one entitled appropriately "The Backyard Foundry" a wealth of really practical information on all aspects of home foundrywork.

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