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kevin gilmore

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Everything posted by kevin gilmore

  1. hey joamat wanna make a couple of test boards before real money is spent?
  2. joamats hand made boards look much better than that. posted latest schematic. Does anyone recognize the tube power supply? And the output tube has 300v cathode to filament on a tube rated at 100v. Does (did) it even work? birgir mentioned this earlier. have a look Image-Hifi.com-62015-Viva-Audio-Solista.pdf (audiograffiti.com) so lots of very high voltages, lots of heat and flammable felt and a horrible point to point job. But wait, there is more, my good friend ray samuels and his A10. 5687 output tubes in srpp configuration running with a plate voltage of 500v. So at peak output voltages the cathode of the top tube sees 500 volts with respect to the cathode on a tube rated at 100v. How does this even work? megatronschem2.PDF
  3. the biggest problem is that the tube sockets are up to .02 inch off in both x and y. really hard to make a circuit board with tube sockets fit into the holes with a top panel that is .35 inch thick. and all the blind holes for the other board mountings were hand tapped and then the holes in the boards were made bigger till it fit. this is so hopelessly fucked. might have to make the holes in the tube sockets much bigger to allow for the slop. No room for a regulated power supply. do want to know how the dremel tool work was done. also corrosion all over the place when the electrolytics let loose. at least we finally have an example that is much worse than the singlepower es2. not sure how to continue.
  4. the input wiring is monster cable magnetically shielded cable. Says so right on the cable. And it was a quad balanced pot wired as unbalanced.
  5. back of circuit board. look at that filament wiring. and the corners notched out of the board. bias board. its even worse, after the 100k resistor 2 x .022uf caps to ground tied directly to the headphones.
  6. So i figured that i would test the 300v supply to see if its worth saving. But no, BOTH transformers are < 1 ohm on the primary. But no way was i expecting this. And the bias resistor for the headphones really is 100k. Very bad for the headphones. A voltage multiplier *7 from 90v. unregulated, no zeners, no protection, no anything. But wait there is more, hand made circuit boards with a dremel tool. This all has to go. But wait, the first picture is a regulated power suppy whose sole job is to drive the power led in the switch.
  7. its here filament transformer for sure smoked. as in hole in the potting likely where the flames were shooting out. has that wonderful singlepower extreme smell. If anyone knows where to get transformers like this made, let me know. specs are as follows. Filament transformer, mounting holes 85mm square threaded with 4.5mm bolts 4 x 6.3 volt at 2 amp 2 x 6.3 volt at 4 amp 1 x 12.6 volt at 1 amp 18 volts @ 1 amp Primary 2 x 115vac High voltage transformer, mounting holes 100mm square threaded with 4.5mm bolts Primary 2 x 115vac 2 x 5 volt at 2 amp 2 x 630volt center tapped at 200ma 510 volt center tapped at 130ma 6.3 volt at 1 amp So many bad solder joints. grounding shields on the small tube sockets essentially force removed with a side cutter. Yikes. Notice the required missing corner out of the new board. Fucking idiot made the case first then found a way to cram everything inside.
  8. https://drive.google.com/drive/folders/1r3g2TAtBUaBdiMorTWX7yYgeJ7maQbYW?usp=sharing new link, files uploading includes all new zip files published since the first upload.
  9. does not work for me either. that google drive is birgirs i think lucky i have all of this backed up in many different locations
  10. a quick game than anyone other than birgir or orientexpedite can play. look at the amp board above. now look at some of the other pictures of the real amp board. anyone know the 4 required major components that are missing? First one gets 10 booby points. hint: https://www.head-case.org/forums/topic/10783-megatron-electrostatic-headphone-amplifier/?do=findComment&comment=551186
  11. stax mafia electrostatic portable in the works. would need the bias adjusted for the shure headphones.
  12. files in the stax mafia google shares.
  13. The output stage at least is definitely megatron. DC coupled with tube current source driving a gain tube. The rest of it has significant changes, why i don't know.
  14. working on this megatron disaster from the pictures. Awaiting delivery of the item to confirm i have not made any mistakes in diagnosing the mikhail class fuckups. 1) The filament windings for the output tubes are all tied together. The 4 current sources are limited to +/-100v before the tubes arc. The gain output tubes are all referenced to ground and that violates the maximum cathode to filament voltage by 300v. This is the same as the singlepower esx disaster and every one of those also blew up. The filament transformer MUST be replaced and all the tubes rewired. which requires removal of the amp board. You need 6 filament windings for the output tubes plus a winding for the input tubes plus a winding for the -15v. left transformer left filament winding (blue wires) (notice tied to ground) for the current stage tubes and right filament winding also tied to ground for gain stage tubes. Since the amp board is missing the first stage current source which was replaced by a resistor to -45v and the second stage current source is missing, its easier to do a new board. 2) The high voltage transformer is also fucked. each 400v power supply is running on half wave rectification which results in amperes of ripple current at 30hz. 2 center tapped windings at 630v required plus pair of filament windings necessary to convert the tube rectifiers to dual full wave rectification. Guess what, new transformer required. even with a solid state rectifier a new transformer is required as the high voltage winding has no center tap. major stupid here. pretty sure i have identified a source for replacement transformers, just need to know the hole sizing and spacing. 3) have not even figured out the +300v supply yet, so many fuckups. So pretty much this is a complete and total rebuild. With the covid economy, could be months to get the repair parts.
  15. i will be posting more about this one next week. The filaments for a megatron MUST BE FLOATING! And this one has them all tied together and referenced to ground. Just like the mikhail esx. And the power supply is half wave with the power caps seeing multiple amperes of peak current. Both power transformers will have to be replaced. The gain tubes have 400v between the cathodes and filaments. (data sheet says 100v max) the mcalister is actually repairable, but its a bunch of work. And those tubes are just about impossible to find.
  16. i just noticed this. amplifier says its push pull amplifier. the megatron is NOT a push pull amplifier. Its dual single ended current source.
  17. this is way to much dc input offset for the servo's to handle
  18. you can use a shorter heatsink. maximum is about .7 watt
  19. that is the bias supply current source and is at at least 700v. best for highest isolation.
  20. oh my god, where to start? The 2 rectifier tubes are GZ34 correct? Full wave tube diodes run as half wave diodes. Why? +/-400v power supply appears to be completely unregulated. 2 x el84+12ax7 is regulated +300v power supply? Original power supply caps rated at 450, definitely not enough. 550v just barely enough and that depends on whether the output tubes are actually warm before the rectifiers get warm. input tube current sources replaced by single power supply and resistor? cascode tube current sources replaced with resistor? Not even sure how i would fix this. But the tube rectifier and unregulated power supply have to go. Probably enough room for a pair of GRHV power supplies (kerry style). 300v supply likely has to go too. If its blowing fuses, could be that the high voltage transformer windings were not rated for >500v wrt ground. Reminds me of mikhail.
  21. littlefuse dalbani littlediode nikko... all the same company. and yes they sell lots of fakes. 2sa1968 are pnp. but if they test as 30v transistors, they are definitely fakes.
  22. don't know about buying parts in india. parts in usa are around $150.
  23. https://www.head-fi.org/threads/stax-srm-007tii-amp-tube-rolling-bias-adjustment.653258/post-16389801 this person published half the schematic. This schematic is similar to, but not the same as your amp which has dc filaments. you need to replace all the parts including the diodes and capacitors. the other high voltage caps don't look very good either. and likely one or more of the tubes are bad.
  24. modifications would be required to lower the bias to 200v from 560. it is unknown whether the headphones can take the extra voltage swing of this amp. one version of this amp will definitely be analog input only. lithium batteries suck. get used to it.
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