| Jeff Urban <jurb6006@gmail.com>: Apr 16 02:26AM -0700 >I did see one page on line where the discussion about replacing G >with S was you double the size of the original G's emitter resistor. >So, if it was 75R you would change that to 150R. Have you any >knowledge of that? This is not making sense here. What is G and what is S ? From what I heard G was gate, the equivalent of the base in a transistor and S was source equivalent to the emitter of a transistor, the C or D of course it the other one. Collector or drain. There is no just changing S for G in any reasonable circuit. If you somehow wanted to reconfigure it to have the current drive drivers run the sources instead of the gates good luck. It'll take a ton of time to do the math to do something that probably will not work. Drivers cannot handle much current, that is why they are not outputs. The schematic link does not work, path not found or some shit. Being a Seeberg I would bet it uses driver transformers. That means to use silicon in it you change two resistors per channel, or perhaps add them to make the new value. Depends on where they fit. Get the print to somewhere accessible so I can have a look at it. |
| Fox's Mercantile <jdangus@att.net>: Apr 16 04:35AM -0500 On 4/16/20 4:26 AM, Jeff Urban wrote: > in a transistor and S was source equivalent to the emitter > of a transistor, the C or D of course it the other one. > Collector or drain. Oh for fuck's sake. Try and keep up will ya? G = Germanium and S = Silicon. -- "I am a river to my people." Jeff-1.0 WA6FWi http:foxsmercantile.com |
| Jeff Urban <jurb6006@gmail.com>: Apr 16 03:02AM -0700 >That will be hard to blow up! >** No hard at all. Well harder than an MJE2955. Harder than a 2N66609. They make oe really tougher pair, MJ2XXXX something. Probaably use those in Krells, just because. I mean they got like 128 output transistors ... nevermind. >I once had boxes of dead ones lying around - mostly extracted from >amplifiers like the Phase linear 400 and 700 mk2s. So those were all the complementary ones,not the quasi like I had. It was a two but still all NPN outputs. And of course when I got it and took it apart I found like four different types or putouts in it. Shit, this is only a 400 so it only has three pairs per channel. >Like any bi-polar, they had limited "safe area" of about 2A at 80V >for 0.5 seconds and much less at higher voltages Well it's not quite THAT bad, but... People do not get it sometimes. "It will be hard to blow that". sure, but if you get it hot enough it will fry. All transistors derate power handling. By 200ºC they can dissipate zero watts. Hot enough those badass MJs will fry, perhaps even from bias current. Not even one watt. The way I take on it it that the thermal resistance to case is what limits that. The die can get so get hot so fast that it doesn't matter how good the heatsink is, it is not moving the heat FAST enough. That 200ºC is the JUNCTION temperature. And even with the best of mounting techniques, I mean run a bead or blob and squish it out so there are no air pockets, do it on clean surfaces and make it tight as hell, the thermal resistance is still atrocious. One of the things I do understand some is power. I make a point of when I fix an amp it stays fixed. So I WILL use MJ15024s ans 15023s in fifty watt per channel amps. Yes the power rating derates like an other, but this one you have to put in a deep fryer. LOL (not really) But then 375ºF is only 190ºC so we got ten degrees to go ! >The lateral Mosfets made by Hitachi that come along in the 1980s >were enormously more rugged. If you got spares to spare I'll take them. But I don't remember right now, were they the ones with the really low Vgs or the ones you can parallel with no source resistors ? And you know source resistors don't work worth a fuck on MOSFETs. I got a circuit that can balance a bank of the much better but, why ? Many people could do the same thing. Ahh, I probably don't have to worry about this right now. A guy is bringing a Tascam, bodybuilder model four track ¼" four track. Nice to do something different once in a while. ACK ! I just looked at the time and I missed my shootemup show of the day. Dammit. Fucking Aussies. |
| "jfeng@my-deja.com" <jfeng@my-deja.com>: Apr 16 06:46AM -0700 On Thursday, April 16, 2020 at 2:26:36 AM UTC-7, Jeff Urban wrote: > The schematic link does not work, path not found or some shit. It weere a t7po errorr; Try using http instead of fttp |
| dplatt@coop.radagast.org (Dave Platt): Apr 15 11:44AM -0700 >information. Is there an all purpose adhesive or epoxy that I can use to >make one big solid mass of plastic? Or do I pretty much have to try the >various adhesives used for different grades of plastic? Plastics can be tricky. The broken surfaces tend to be fairly smooth, which doesn't give epoxy much opportunity to "grab" onto it and make a good mechanical bond. Also, some common plastics have a "low surface energy" issue - put simplistically (and not quite correctly) this means that the surface of the plastic has relatively few chemically-reactive sites on it, to which the epoxy resin could create a chemical bond. So, without good mechanical or chemical bonds, you end up with a glue joint that's not held together very strongly, and it breaks apart easily. I've had good luck on plastics using a thickened epoxy called G-Flex 655. It's sold by West System (a.k.a. West Marine) specifically for use in repairing plastic and fiberglass boats. In my experience it's an excellent all-around repair epoxy for most materials. A friend of mine used it to bond steel pipes and flanges to sheets of granite, after roughing up the granite surface with some emery paper. When he tested it by banging sideways on the pipe with a sledgehammer, the epoxy didn't fail... instead, the granite itself "tore apart" - the rock pulled apart into separate crystals. This stuff has become my "go-to" repair epoxy. There are two tricks you can/should use when bonding difficult plastics. The first is to roughen the surfaces with some sandpaper, giving the material some "tooth" into which the epoxy can flow and then harden - this gives you a better mechanical bond. The second is flaming. Take a propane and butane torch set on a fairly low flame. *Quickly* pass the very tip of the flame over the area to be bonded. You don't want to heat the plastic up enough that it melts, or even starts to soften... you simply want to let the tip of the flame oxidize the very surface of the plastic. This helps deal with the "low surface energy" issue, by creating reactive sites to which the epoxy resin can create a chemical bond. If you buy the West System G-Flex 655 boat-repair kit, you get two very generous tubes of epoxy, some sandpaper, gloves, and "plastic boat repair" instructions which goes through the above procedures in detail. You can buy just the epoxy (without the extras) for a bit less money. It's a more expensive initial purchase than the little tubes you'll find at a hardware store, but it'll be enough to last you for years. |
| Jeff Liebermann <jeffl@cruzio.com>: Apr 15 05:11PM -0700 On Wed, 15 Apr 2020 11:44:44 -0700, dplatt@coop.radagast.org (Dave Platt) wrote: >less money. It's a more expensive initial purchase than the little >tubes you'll find at a hardware store, but it'll be enough to last you >for years. G/Flex 650 is the less viscous mix. <https://www.westsystem.com/specialty-epoxies/gflex-650-toughened-epoxy/> G/Flex 655 is the thickened mixture. <https://www.westsystem.com/specialty-epoxies/gflex-655-thickened-epoxy-adhesive/> G/FLex 650 can be converted into the thicker G/Flex 655 by adding 406 Colloidal Silica: <https://www.westsystem.com/406-colloidal-silica/> However, I've never tried it. Both epoxies require some form of surface preparation. <https://www.westsystem.com/specialty-epoxies/gflex-epoxy-adhesion-data/> Notice that the adhesion strength increases substantially with sandpapering, alcohol wipe, and flame treating. -- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
| Mike S <mscir@yahoo.com>: Apr 15 09:01PM -0700 On 4/15/2020 4:19 AM, HW wrote: > will not be able to last, even with a glue that works. Sometimes, a > mechanical repair can be used. Some sort of bracket or clip that is > screwed in place, for example. Thanks, and I agree, I think I'll glue it and then wrap an aluminum brace around the perimeter to add additional strength. |
| Mike S <mscir@yahoo.com>: Apr 15 09:02PM -0700 On 4/15/2020 11:44 AM, Dave Platt wrote: > less money. It's a more expensive initial purchase than the little > tubes you'll find at a hardware store, but it'll be enough to last you > for years. Thanks Dave. |
| Mike S <mscir@yahoo.com>: Apr 15 09:14PM -0700 On 4/15/2020 5:11 PM, Jeff Liebermann wrote: > <https://www.westsystem.com/specialty-epoxies/gflex-epoxy-adhesion-data/> > Notice that the adhesion strength increases substantially with > sandpapering, alcohol wipe, and flame treating. Thanks Jeff, their video is funny and impressive. https://www.youtube.com/watch?time_continue=22&v=2a5RlcP-4JE&feature=emb_logo |
| amdx <nojunk@knology.net>: Apr 16 08:08AM -0500 On 4/14/2020 11:07 PM, Mike S wrote: On many of my plastic repairs, I strengthen them be drilling and inserting a 0.025" steel rod that I glue in place. Sometimes two, if it is large enough. Sometimes I temporarily glue it in place to get proper alignment while drilling. It has saved me a lot of time waiting for parts. I also have a drill and tap for a 1-72 screw if that is needed. As you are aware, it breaks where at the point where it needs the most reinforcement. Mikek |
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