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kevin gilmore

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Everything posted by kevin gilmore

  1. So this started a few weeks ago when someone found a picture of my 100 watt night light. Its an 833A tube. (new picture below) And he wanted a megatron made from 8 of these. (10 vac at 10 amps each tube) so 800 watts filament power just for the output tubes. By the time you make the +/- 1kv power supplies running at 40ma, and the power for the 300b driver tubes etc, way past the limit for usa 120v 20 amp service which is 1850 watts. And with the top of the tube at silly and dangerous high voltage... bad idea. So i started looking for slightly less silly alternatives. I think the 211 tube fits the bill. running with +/-750v power supplies at 35ma. So a megatron with 211 output tubes, 300b drivers and a high gain input tube. unless someone has a better idea.
  2. depends on what kind of power supply is inside. if its a switcher, it might benefit the input caps for a 30 second slow ramp. if its a linear supply, probably does not matter.
  3. my orbi is getting glitchy too. replacement is $1500. likes to drop the dns once a week. i'm getting 1194 download and 24 upload. if i get the newest orbi, i can get up to about 1600 download with top xfinity tier. i don't need that yet, and then i would have to upgrade every switch in the house to 2gb or faster, and those are expensive too. also looks like i'm going to get a atsc 3.0 tuner very soon. there is a chicago station now that is broadcasting 4k cartoons. 3 stooges in 4k is da bomb.
  4. i don't remember. definitely can add 1 wire and not use it in shunt mode.
  5. you are going to need to change the lt1021 to the 5v version and recalculate the resistor ratio. 3v across the current source is not enough for it to work properly. even 5 volts is cutting it close. the minimum tested voltage for this design is 12v output.
  6. clever idea but you then need a jumper block.
  7. switch the tubes. if the hum does not move, its the headphones.
  8. unless one of the tubes is slammed to one of the rails, rebiasing is not going to help. but you should measure the dc output voltages.
  9. cp1117n is normally closed, so no output voltage. you need to power it to turn the hv on.
  10. kgsshvpssicfetsinglenewleftfatsws - cadcam.zip 12/25/2015 definitely on the google drive.
  11. i posted this elsewhere. here is a copy Its all about size (as in core cross sectional area) and maximum flux before saturation. its obvious from the graphs above (posted elsewhere) that the core saturation of the eha5 transformer is about 1.4 tesla indicating the cheapest of core materials. better and much bigger transformers are available from lundahl and edcor. which will both give 20hz to 20khz +0 -1 db and will actually do 1800vpp with a 50 watt amplifier over the full frequency band. without series resistors. without filters. as far as i can tell lundahl does not specify maximum field strength. edcor does and its 2.01 tesla. there are custom c cores with magic materials that can do up to 2.5 tesla. these are a bit expensive. the ll1630 mentioned above (posted elsewhere) will NOT do this. core size is too small. you need a transformer with a minimum of a 30 watt core. The 60 watt edcor are MUCH better. the ifi iesl which is extremely sensitive to power amplifiers is yet another example of a poor design with a tiny transformer. does not matter how carefully you wind the core if you drive the transformer into saturation. the result will be a box about 3 times the size of the eha5. and a weight of about 20 lbs. cost about $600. nope, no cheap way of doing this.
  12. here is a link to simmcon's takedown of the eha5. its mandatory reading for everyone. https://www.audiosciencereview.com/forum/index.php?threads/topping-eha5.42149/post-1712440 in other news, birgir sent me a srd7 to test. in other other news, i have finally found a company that will sell me cores and bobbins in small quantities. so making electrostatic transformers becomes a possibility.
  13. so here are some more pictures, obviously faked. This is the kgsshv-carbon built by birgir and given to tyll as one of his 2 reference amps. Into a standard 120pf load. right at the limit of my scope probe, have to find the higher voltage probes. first picture 20 volts per division, next 2 are 50 volts per division. all are 10khz square wave. reference cap beginning to bubble due to heat.
  14. well if i used one of my digital scopes, then did an edit on the computer and then played it back on the scope, its probably fairly easy. but on a real analog scope, it would be some kind of impossible.
  15. So a person accused me of faking my scope picture, because it had to be my signal generator. And that the amp performed better at the higher gain setting. I completely disagree. Q15 has no emitter resistor and the resulting gain of just this transistor is 30db. which makes the miller capacitance absolutely huge. which is why you see two different slew rates. the first bit is due to the output amp (everything left of r12 which is a diamond buffer driving a pair of current mirrors driving another diamond buffer). The second bit is due to Q15. edit: shenzen audio is now selling these things brand new in the box on ebay for $50 off. soon it will be $100 off.
  16. nope, you cannot use this. reverse bias and the diaphram accumulates all the dust particles. a month later and your headphones are trash.
  17. its easier to do the board, then let the software turn it back into a schematic update: should be final schematic. that is a 3 pole (18db) low pass filter at 18khz. part of schematic now. nfca3.PDF
  18. sure, +/-24v at 5 amps each rail balanced drive large heatsinks custom hand wound bifilar transformer with a really large cross section to keep the flux as low as possible and magic hybrid core ferrite materials. $$$
  19. success soon yep, 39 transistors including 2 dual matched npn.
  20. so you say you should be able to measure why it sounds like it does... first 2 are 1khz into 50 ohm non-inductive load. notice that the rise time and fall time are not identical. also notice severe slew rate limiting in both directions and kink on the positive slope. 3rd picture is 10khz. kind of what you would expect from an amplifier with an open loop gain of around 120db and a group delay of 10us or more. i don't have the transformers, but i'll bet it looks even worse driving that transformer. pretty sure the a90d will perform exactly the same. edit: see pictures in next post. definitely same as a90d
  21. So, after a few hours in my favorite combination of methylene chloride, acetone, toluene, benzene, and 2 other magic ingredients (basically miller-stephenson ms111 only way cheaper) Warning kids: don't try this at home. highly flammable, highly toxic, low flash point... Let the professional morons do this the eha5 discrete module in the process of giving up its secrets. every single part of the eha5 is a massive pile of crap. it takes a whole room full of highly competent engineers to produce something this fucked up. i did take the other module, hooked it up to a bench supply and hd800 headphones and got a good listen. wow is this bad. proof that obviously the lowest distortion possible in amir's s/n test is the one and only measurement that they think matters. the rest of the specs, not even close. for those that don't know, the external power brick is a single 15v switching supply at 3 amps. internally it makes -15 from the +15. except for the fact that the -15 supply seems limited to about 750ma, and it runs 4 amps from this. So maybe if you are lucky you get about 175ma max current per amplifier. No way this is enough to drive those crap transformers. transistors are 2L, G1 and the dual is k4r
  22. the phase is going to mess with the feedback in a serious way. going to be very tricky to get right. and then there is the problem of disconnecting the headphones with audio playing. might turn into a high power oscillator.lots of magic smoke.
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