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Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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#1
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Porcelain thermally conductive insulators ?
1.8mm slabs of porcelain under TO220 devices.
(This is continuation of Ampeg BA600-115, can of worms. I've got mains back on it and is in working order , now to try with high power.) This is my educated guess as to what happened at manufacture as absent but distinctive 20mm long bolt not found around here. The 4 output devices should be held to the heatsink via a cross-bar over all 4 of them and 2 bolts thru it into the heatsink. The insulators are ceramic and the 2 central ones, butted up together , do not clear the retaining bolts on their outer edges. After graunching the thread the assembler decided to leave it out and trust to luck one off-centre bolt would hold. Coming to reassembly I found a 3mm screw for replacement but it would not hold, as tapped thread is stripped, so I tapped that one hole out to 4mm. Tried grinding a clearance notch on the side of one pad but got nowhere as ceramic. Not only that but I had no trouble holding the slab in fingers while trying to grind a slot , it was barely getting warm - good thermal insulator or small grinding wheel not generating heat as not cutting into the material ? So ,lateral thinking, decided to grind down the screw thread where it interferes with the ceramic , on one bolt. I wonder if this was a one off at manufacture or a whole batch like this, all that was needed was shift a tapped hole 1mm, plenty of room there for that. Or one ceramic pad 1 or 2 mm narrower. ps anyone use "chain mail glove" for small part in-hand grinding? At 80GBP and upwards unlikely , firstly on cost, second need fingers for gripping items. As an experiment wound some kevlar (ex fibre optic leads) around finger of old glove and held in place with hot melt string. Simulated grabbing/skittering of Dremmel and grinding disc into this on a piece of dowel. It did not penetrate to the dowel, I expected the kevlar to snag and stall the motor but cut clean through. |
#2
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Porcelain thermally conductive insulators ?
N_Cook Inscribed thus:
1.8mm slabs of porcelain under TO220 devices. I would check that ! Its more likely that they are Beryllium_oxide ! http://en.wikipedia.org/wiki/Beryllium_oxide Tried grinding a clearance notch on the side of one pad but got nowhere as ceramic. Not only that but I had no trouble holding the slab in fingers while trying to grind a slot, it was barely getting warm - good thermal insulator or small grinding wheel not generating heat as not cutting into the material ? The dust from grinding or abrading Beryllium_oxide is highly toxic ! -- Best Regards: Baron. |
#3
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WARNING! Porcelain thermally conductive insulators ?
"N_Cook" wrote in message
... 1.8mm slabs of porcelain under TO220 devices. (This is continuation of Ampeg BA600-115, can of worms. I've got mains back on it and is in working order , now to try with high power.) This is my educated guess as to what happened at manufacture as absent but distinctive 20mm long bolt not found around here. The 4 output devices should be held to the heatsink via a cross-bar over all 4 of them and 2 bolts thru it into the heatsink. The insulators are ceramic and the 2 central ones, butted up together , do not clear the retaining bolts on their outer edges. After graunching the thread the assembler decided to leave it out and trust to luck one off-centre bolt would hold. Coming to reassembly I found a 3mm screw for replacement but it would not hold, as tapped thread is stripped, so I tapped that one hole out to 4mm. WARNING Tried grinding a clearance notch on the side of one pad but got nowhere as ceramic. WARNING Not only that but I had no trouble holding the slab in fingers while trying to grind a slot , it was barely getting warm - good thermal insulator or small grinding wheel not generating heat as not cutting into the material ? So ,lateral thinking, decided to grind down the screw thread where it interferes with the ceramic , on one bolt. {snip} Those ceramic insulators are made from beryllia (berylium oxide), a ceramic that has a higher heat conductivity than aluminum. You should be _extremely_ careful in handling them. Quoting from the Wikipedia article: "Like all berylium compounds, BeO is carcinogenic and may cause chronic beryllium disease. Once fired into solid form, it is safe to handle as long as it is not subjected to any machining that generates dust." Likewise the American Beryllia site says: "Exposure to fine, airborne beryllium oxide powder or dust in sufficiently large concentrations, may cause a lung disease in a small number of hypersensitive people." Grinding a beryllia insulator is considered exceptionally dangerous. Please read the MSDS at http://www.AmericanBeryllia.com/lit/...Oxide_MSDS.pdf. I once needed some microwave windows made of beryllia. I was going to order beryllia blanks, have the edges sputtered in gold, and braze them into 316 stainless waveguide sections. I called the engineers at National Beryllia (now American Beryllia) to discuss this application. In short order, they convinced me that they should manufacture the windows as there was a chance that the differential thermal expansion between the beryllia and the stainless steel waveguide could potentially shatter the ceramic and release beryllia powder. After learning the cost, I went with sapphire windows instead. Some people are hypersensitive to beryllium compounds. If you are not in the hospital yet, consider yourself _very_ lucky. A small percentage of the population is so hypersensitive that the small amount of dust you created could be lethal. Dr. Barry L. Ornitz WA4VZQ [my_ham_call at live.com] |
#4
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Porcelain thermally conductive insulators ?
"N_Cook" wrote in :
1.8mm slabs of porcelain under TO220 devices. (This is continuation of Ampeg BA600-115, can of worms. I've got mains back on it and is in working order , now to try with high power.) This is my educated guess as to what happened at manufacture as absent but distinctive 20mm long bolt not found around here. The 4 output devices should be held to the heatsink via a cross-bar over all 4 of them and 2 bolts thru it into the heatsink. The insulators are ceramic and the 2 central ones, butted up together , do not clear the retaining bolts on their outer edges. After graunching the thread the assembler decided to leave it out and trust to luck one off-centre bolt would hold. Coming to reassembly I found a 3mm screw for replacement but it would not hold, as tapped thread is stripped, so I tapped that one hole out to 4mm. Tried grinding a clearance notch on the side of one pad but got nowhere as ceramic. Not only that but I had no trouble holding the slab in fingers while trying to grind a slot , it was barely getting warm - good thermal insulator or small grinding wheel not generating heat as not cutting into the material ? So ,lateral thinking, decided to grind down the screw thread where it interferes with the ceramic , on one bolt. I wonder if this was a one off at manufacture or a whole batch like this, all that was needed was shift a tapped hole 1mm, plenty of room there for that. Or one ceramic pad 1 or 2 mm narrower. ps anyone use "chain mail glove" for small part in-hand grinding? At 80GBP and upwards unlikely , firstly on cost, second need fingers for gripping items. As an experiment wound some kevlar (ex fibre optic leads) around finger of old glove and held in place with hot melt string. Simulated grabbing/skittering of Dremmel and grinding disc into this on a piece of dowel. It did not penetrate to the dowel, I expected the kevlar to snag and stall the motor but cut clean through. they may be -alumina- slabs,not porcelain;TEK used to use ~5/8" sq. alumina slabs under the LVPS pass transistors on the 5000 series o'scope mainframes. -- Jim Yanik jyanik at localnet dot com |
#5
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Porcelain thermally conductive insulators ?
Baron wrote in message
... N_Cook Inscribed thus: 1.8mm slabs of porcelain under TO220 devices. I would check that ! Its more likely that they are Beryllium_oxide ! http://en.wikipedia.org/wiki/Beryllium_oxide Tried grinding a clearance notch on the side of one pad but got nowhere as ceramic. Not only that but I had no trouble holding the slab in fingers while trying to grind a slot, it was barely getting warm - good thermal insulator or small grinding wheel not generating heat as not cutting into the material ? The dust from grinding or abrading Beryllium_oxide is highly toxic ! -- Best Regards: Baron. Unfortunately it would not grind. I assume it was not heating up because the grinding disc was just running over the surface without even rubbing , let alone grinding, so no dust, still the flat edge . Does BeO have that sort of translucent appearance of porcelain? I've managed to grind small sections of the ceramic used is high temperature "chock block" connectors, that has a normal solid white appearance. But given its use here then presumably BeO. It was the slightly milky/translucent porcelain-like appearance that convinced me. |
#6
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Porcelain thermally conductive insulators ?
On Tue, 19 Apr 2011 08:25:39 +0100, "N_Cook" wrote:
Baron wrote in message ... N_Cook Inscribed thus: 1.8mm slabs of porcelain under TO220 devices. I would check that ! Its more likely that they are Beryllium_oxide ! http://en.wikipedia.org/wiki/Beryllium_oxide Tried grinding a clearance notch on the side of one pad but got nowhere as ceramic. Not only that but I had no trouble holding the slab in fingers while trying to grind a slot, it was barely getting warm - good thermal insulator or small grinding wheel not generating heat as not cutting into the material ? The dust from grinding or abrading Beryllium_oxide is highly toxic ! -- Best Regards: Baron. Unfortunately it would not grind. I assume it was not heating up because the grinding disc was just running over the surface without even rubbing , let alone grinding, so no dust, still the flat edge . Does BeO have that sort of translucent appearance of porcelain? I've managed to grind small sections of the ceramic used is high temperature "chock block" connectors, that has a normal solid white appearance. But given its use here then presumably BeO. It was the slightly milky/translucent porcelain-like appearance that convinced me. Only BeO I've seen was pink, and I'd not try to grind it, toxic! Safe if not shattered. Grant. |
#7
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Porcelain thermally conductive insulators ?
Grant wrote in message
... On Tue, 19 Apr 2011 08:25:39 +0100, "N_Cook" wrote: Baron wrote in message ... N_Cook Inscribed thus: 1.8mm slabs of porcelain under TO220 devices. I would check that ! Its more likely that they are Beryllium_oxide ! http://en.wikipedia.org/wiki/Beryllium_oxide Tried grinding a clearance notch on the side of one pad but got nowhere as ceramic. Not only that but I had no trouble holding the slab in fingers while trying to grind a slot, it was barely getting warm - good thermal insulator or small grinding wheel not generating heat as not cutting into the material ? The dust from grinding or abrading Beryllium_oxide is highly toxic ! -- Best Regards: Baron. Unfortunately it would not grind. I assume it was not heating up because the grinding disc was just running over the surface without even rubbing , let alone grinding, so no dust, still the flat edge . Does BeO have that sort of translucent appearance of porcelain? I've managed to grind small sections of the ceramic used is high temperature "chock block" connectors, that has a normal solid white appearance. But given its use here then presumably BeO. It was the slightly milky/translucent porcelain-like appearance that convinced me. Only BeO I've seen was pink, and I'd not try to grind it, toxic! Safe if not shattered. Grant. I've seen pink TO3, presumably BeO, insulators before but they did not have this transclucent like appearance. |
#8
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Porcelain thermally conductive insulators ?
N_Cook Inscribed thus:
Baron wrote in message ... N_Cook Inscribed thus: 1.8mm slabs of porcelain under TO220 devices. I would check that ! Its more likely that they are Beryllium_oxide ! http://en.wikipedia.org/wiki/Beryllium_oxide Tried grinding a clearance notch on the side of one pad but got nowhere as ceramic. Not only that but I had no trouble holding the slab in fingers while trying to grind a slot, it was barely getting warm - good thermal insulator or small grinding wheel not generating heat as not cutting into the material ? The dust from grinding or abrading Beryllium_oxide is highly toxic ! -- Best Regards: Baron. Unfortunately it would not grind. I assume it was not heating up because the grinding disc was just running over the surface without even rubbing , let alone grinding, so no dust, still the flat edge. Does BeO have that sort of translucent appearance of porcelain? The surface tends to have the appearance of good quality photocopy paper, very smooth with a barely visible grain. A bit like ferrite beads. I've managed to grind small sections of the ceramic used is high temperature "chock block" connectors, that has a normal solid white appearance. But given its use here then presumably BeO. It was the slightly milky/translucent porcelain-like appearance that convinced me. Both Aluminum oxide and Beryllium oxide are extremely hard materials. I belive that the pink dye was used later to specifically identify Beryllium. So its a good chance that the white insulators that you have are Aluminum oxide. Even so its not a good idea to try to grind them. Ceramics are also used to machine metals, including some that are so tough that only ceramic cutters can be used on them. -- Best Regards: Baron. |
#9
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Porcelain thermally conductive insulators ?
"Baron" wrote in message
... Both Aluminum oxide and Beryllium oxide are extremely hard materials. I belive that the pink dye was used later to specifically identify Beryllium. So its a good chance that the white insulators that you have are Aluminum oxide. Even so its not a good idea to try to grind them. Beryllia is white, the same as alumina. There is no standard on coloring beryllia insulators for use as heat transfer links. No dye is used as the beryllia is sintered (fired) at very high temperatures. Instead a colored inorganic metal oxide is added in small amounts. Beryllia has about seven to ten times the thermal conductivity of alumina, so if the links were used with high power parts, they are probably beryllia. Beryllia has about one third better thermal conductivity than aluminum nitride in the 25 to 300 C temperature range. Only diamond and cubic boron nitride are better thermal conductors (but at an exceptionally high cost). Until you know for sure what these insulators are made of, treat them as beryllia. I.e., do not grind or crush them. 73, Dr. Barry L. Ornitz WA4VZQ |
#10
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Porcelain thermally conductive insulators ?
Baron wrote: Both Aluminum oxide and Beryllium oxide are extremely hard materials. I belive that the pink dye was used later to specifically identify Beryllium. The 4CX250 transmitter tubes I used had white BeO ceramic insulators. -- You can't fix stupid. You can't even put a Band-Aid™ on it, because it's Teflon coated. |
#11
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Porcelain thermally conductive insulators ?
Baron wrote in message
... N_Cook Inscribed thus: Baron wrote in message ... N_Cook Inscribed thus: 1.8mm slabs of porcelain under TO220 devices. I would check that ! Its more likely that they are Beryllium_oxide ! http://en.wikipedia.org/wiki/Beryllium_oxide Tried grinding a clearance notch on the side of one pad but got nowhere as ceramic. Not only that but I had no trouble holding the slab in fingers while trying to grind a slot, it was barely getting warm - good thermal insulator or small grinding wheel not generating heat as not cutting into the material ? The dust from grinding or abrading Beryllium_oxide is highly toxic ! -- Best Regards: Baron. Unfortunately it would not grind. I assume it was not heating up because the grinding disc was just running over the surface without even rubbing , let alone grinding, so no dust, still the flat edge. Does BeO have that sort of translucent appearance of porcelain? The surface tends to have the appearance of good quality photocopy paper, very smooth with a barely visible grain. A bit like ferrite beads. I've managed to grind small sections of the ceramic used is high temperature "chock block" connectors, that has a normal solid white appearance. But given its use here then presumably BeO. It was the slightly milky/translucent porcelain-like appearance that convinced me. Both Aluminum oxide and Beryllium oxide are extremely hard materials. I belive that the pink dye was used later to specifically identify Beryllium. So its a good chance that the white insulators that you have are Aluminum oxide. Even so its not a good idea to try to grind them. Ceramics are also used to machine metals, including some that are so tough that only ceramic cutters can be used on them. -- Best Regards: Baron. The next time I come across one I'll try passing a laser beam or bright light through it to see if any light passes through. It was that translucency appearance, like porcelain , that I noticed. |
#12
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Porcelain thermally conductive insulators ?
I had to get inside that amp again, yet another PbF problem from next to
zero insertion force speaker connector at the PA 4 removal & inserts by me was enough , only 6 months old. The slabs pass red laser pointer light, but then on checking but so does the ceramic of high temp "choc block". These slabs are more trnasmissive and scatter the light throughout the slab not just the entry and exit area of the chock block. |
#13
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Porcelain thermally conductive insulators ?
N_Cook Inscribed thus:
I had to get inside that amp again, yet another PbF problem from next to zero insertion force speaker connector at the PA 4 removal & inserts by me was enough , only 6 months old. The slabs pass red laser pointer light, but then on checking but so does the ceramic of high temp "choc block". These slabs are more trnasmissive and scatter the light throughout the slab not just the entry and exit area of the chock block. Mmm ! Interesting. I have a small quantity of boxed TO3 BeO insulators. I'll have to get one out and see. -- Best Regards: Baron. |
#14
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Porcelain thermally conductive insulators ?
On Mon, 18 Apr 2011 17:36:42 +0100, Baron wrote:
N_Cook Inscribed thus: 1.8mm slabs of porcelain under TO220 devices. I would check that ! Its more likely that they are Beryllium_oxide ! http://en.wikipedia.org/wiki/Beryllium_oxide Tried grinding a clearance notch on the side of one pad but got nowhere as ceramic. Not only that but I had no trouble holding the slab in fingers while trying to grind a slot, it was barely getting warm - good thermal insulator or small grinding wheel not generating heat as not cutting into the material ? The dust from grinding or abrading Beryllium_oxide is highly toxic ! BeO is very expensive. I would be very surprised to find any in such application. |
#15
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Porcelain thermally conductive insulators ?
josephkk wrote in message
... On Mon, 18 Apr 2011 17:36:42 +0100, Baron wrote: N_Cook Inscribed thus: 1.8mm slabs of porcelain under TO220 devices. I would check that ! Its more likely that they are Beryllium_oxide ! http://en.wikipedia.org/wiki/Beryllium_oxide Tried grinding a clearance notch on the side of one pad but got nowhere as ceramic. Not only that but I had no trouble holding the slab in fingers while trying to grind a slot, it was barely getting warm - good thermal insulator or small grinding wheel not generating heat as not cutting into the material ? The dust from grinding or abrading Beryllium_oxide is highly toxic ! BeO is very expensive. I would be very surprised to find any in such application. ++++ These were not made for the job. They have a hole for either TO220 or TOP66 maybe size transistors . So too wide for this use and the hole is not used .. The layout does not mean they have to be 1.8mm thick , any thickness from mica up could have been accommodated. Normally you would go for the thinnest of insulators. |
#16
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Porcelain thermally conductive insulators ?
Baron wrote in message
... N_Cook Inscribed thus: I had to get inside that amp again, yet another PbF problem from next to zero insertion force speaker connector at the PA 4 removal & inserts by me was enough , only 6 months old. The slabs pass red laser pointer light, but then on checking but so does the ceramic of high temp "choc block". These slabs are more trnasmissive and scatter the light throughout the slab not just the entry and exit area of the chock block. Mmm ! Interesting. I have a small quantity of boxed TO3 BeO insulators. I'll have to get one out and see. -- Best Regards: Baron. It maybe a function of thickness, these being 1.8mm thick slabs rather than wafers |
#17
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Porcelain thermally conductive insulators ?
josephkk Inscribed thus:
On Mon, 18 Apr 2011 17:36:42 +0100, Baron wrote: N_Cook Inscribed thus: 1.8mm slabs of porcelain under TO220 devices. I would check that ! Its more likely that they are Beryllium_oxide ! http://en.wikipedia.org/wiki/Beryllium_oxide Tried grinding a clearance notch on the side of one pad but got nowhere as ceramic. Not only that but I had no trouble holding the slab in fingers while trying to grind a slot, it was barely getting warm - good thermal insulator or small grinding wheel not generating heat as not cutting into the material ? The dust from grinding or abrading Beryllium_oxide is highly toxic ! BeO is very expensive. I would be very surprised to find any in such application. I wonder how much 12 dozen TO3 BeO insulators would be worth ? -- Best Regards: Baron. |
#18
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Porcelain thermally conductive insulators ?
N_Cook Inscribed thus:
Baron wrote in message ... N_Cook Inscribed thus: I had to get inside that amp again, yet another PbF problem from next to zero insertion force speaker connector at the PA 4 removal & inserts by me was enough , only 6 months old. The slabs pass red laser pointer light, but then on checking but so does the ceramic of high temp "choc block". These slabs are more trnasmissive and scatter the light throughout the slab not just the entry and exit area of the chock block. Mmm ! Interesting. I have a small quantity of boxed TO3 BeO insulators. I'll have to get one out and see. -- Best Regards: Baron. It maybe a function of thickness, these being 1.8mm thick slabs rather than wafers I cracked open a box of TO3 BeO insulators this afternoon... I was very surprised ! I tried shining a red laser pointer through one. Its weird but they do seem to glow but no direct light through it. Putting one against a small hole in a cardboard box and viewing the sun shows nothing, no light, nothing. Most odd ! -- Best Regards: Baron. |
#19
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Porcelain thermally conductive insulators ?
Baron wrote in message
... N_Cook Inscribed thus: Baron wrote in message ... N_Cook Inscribed thus: I had to get inside that amp again, yet another PbF problem from next to zero insertion force speaker connector at the PA 4 removal & inserts by me was enough , only 6 months old. The slabs pass red laser pointer light, but then on checking but so does the ceramic of high temp "choc block". These slabs are more trnasmissive and scatter the light throughout the slab not just the entry and exit area of the chock block. Mmm ! Interesting. I have a small quantity of boxed TO3 BeO insulators. I'll have to get one out and see. -- Best Regards: Baron. It maybe a function of thickness, these being 1.8mm thick slabs rather than wafers I cracked open a box of TO3 BeO insulators this afternoon... I was very surprised ! I tried shining a red laser pointer through one. Its weird but they do seem to glow but no direct light through it. Putting one against a small hole in a cardboard box and viewing the sun shows nothing, no light, nothing. Most odd ! -- Best Regards: Baron. Thast was the same here complete scarttering with no obvious bright spot directly opposite the entry point. Chock block ceramic was just the adjascent bright spot , much attenuated in comparison to the porcelain or vitrified BeO slab |
#20
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Porcelain thermally conductive insulators ?
On Thu, 21 Apr 2011 21:15:25 +0100, Baron wrote:
josephkk Inscribed thus: On Mon, 18 Apr 2011 17:36:42 +0100, Baron wrote: N_Cook Inscribed thus: 1.8mm slabs of porcelain under TO220 devices. I would check that ! Its more likely that they are Beryllium_oxide ! http://en.wikipedia.org/wiki/Beryllium_oxide Tried grinding a clearance notch on the side of one pad but got nowhere as ceramic. Not only that but I had no trouble holding the slab in fingers while trying to grind a slot, it was barely getting warm - good thermal insulator or small grinding wheel not generating heat as not cutting into the material ? The dust from grinding or abrading Beryllium_oxide is highly toxic ! BeO is very expensive. I would be very surprised to find any in such application. I wonder how much 12 dozen TO3 BeO insulators would be worth ? The last time i saw a price they were over US $1 each, but that was over 30 years ago and for military use. Between the now rabid regulation and the expected cost i would be rather surprised to find them in commercial instrument amplifiers. Of course with Chinese manufacture such bets may be knocked into a cocked hat. |
#21
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Porcelain thermally conductive insulators ?
josephkk Inscribed thus:
On Thu, 21 Apr 2011 21:15:25 +0100, Baron wrote: josephkk Inscribed thus: On Mon, 18 Apr 2011 17:36:42 +0100, Baron wrote: N_Cook Inscribed thus: 1.8mm slabs of porcelain under TO220 devices. I would check that ! Its more likely that they are Beryllium_oxide ! http://en.wikipedia.org/wiki/Beryllium_oxide Tried grinding a clearance notch on the side of one pad but got nowhere as ceramic. Not only that but I had no trouble holding the slab in fingers while trying to grind a slot, it was barely getting warm - good thermal insulator or small grinding wheel not generating heat as not cutting into the material ? The dust from grinding or abrading Beryllium_oxide is highly toxic ! BeO is very expensive. I would be very surprised to find any in such application. I wonder how much 12 dozen TO3 BeO insulators would be worth ? The last time i saw a price they were over US $1 each, but that was over 30 years ago and for military use. Between the now rabid regulation and the expected cost i would be rather surprised to find them in commercial instrument amplifiers. Of course with Chinese manufacture such bets may be knocked into a cocked hat. You mentioned "military use", the original packing had "Marconi" on the label ! I've had them for more than 20 years. They came as part of an auction lot. If I recall, a subcontracting company that went bust when Marconi was taken over. -- Best Regards: Baron. |
#22
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Porcelain thermally conductive insulators ?
josephkk wrote in message
... On Thu, 21 Apr 2011 21:15:25 +0100, Baron wrote: josephkk Inscribed thus: On Mon, 18 Apr 2011 17:36:42 +0100, Baron wrote: N_Cook Inscribed thus: 1.8mm slabs of porcelain under TO220 devices. I would check that ! Its more likely that they are Beryllium_oxide ! http://en.wikipedia.org/wiki/Beryllium_oxide Tried grinding a clearance notch on the side of one pad but got nowhere as ceramic. Not only that but I had no trouble holding the slab in fingers while trying to grind a slot, it was barely getting warm - good thermal insulator or small grinding wheel not generating heat as not cutting into the material ? The dust from grinding or abrading Beryllium_oxide is highly toxic ! BeO is very expensive. I would be very surprised to find any in such application. I wonder how much 12 dozen TO3 BeO insulators would be worth ? The last time i saw a price they were over US $1 each, but that was over 30 years ago and for military use. Between the now rabid regulation and the expected cost i would be rather surprised to find them in commercial instrument amplifiers. Of course with Chinese manufacture such bets may be knocked into a cocked hat. ++++ I'm assuming boards soldered up in China but assembled into the cab in USA. So these insulators would likely be fitted in the USA. They obviously were not made for the job, wrong cross-section area, unnecessarily thick, hole not used - perhaps they just had them laying around. That grey silipad could have been used with FET legs preformed to accommodate. |
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