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Showing content with the highest reputation on 04/05/2022 in all areas

  1. It's doing really good. I'm guessing another few weeks and I can lose the bandage.
    3 points
  2. Russia Threatens Wikipedia With $50K Fine for Ignoring Ukraine Warning. 🤡
    3 points
  3. Got a chance to use some of the new tools working at the boss' house.
    3 points
  4. 100% home made dinner from last night: jalepeno poppers, mac and cheese, brisket, slaw, cornbread. The teenager took this to snap to her friends, so excuse the perspective, clipping, etc.
    3 points
  5. The saga of messing with my 2nd Carbon build continues. Since the circuit is very close to the Grounded Grid, I'd like to give it a try. Being hesitant to spend big bucks on a nice quad EL34, I have been on the lookouts for a cheaper substitute. The curve of a pentode looks a lot like that of a SiC FET. I need a pentode with the following properties: The plate curve should have low kinks or no kinks at the low Va range. The lower the 'knee' the better. Low Ig2. Ig2 should be much smaller than Ia (20mA), ideally 1mA or less under the operational Va range such that Ig2 doesn't interfere with cathode drive/ cathode degeneration. The amount of negative bias needed to get 20mA at 400V should be reasonably easy to handle. High rated Va(max) and Pa(max) for using a higher supply voltage and/or idle current in the future. That means I may need to look into transmitting tubes. And the candidate is... (drum roll please) the FU-50/GU-50! The linearity looks pretty good at around Ia=20mA, from Va=100V all the way to 1kV! The bias voltage is between -20V and -25V, right around what Carbon has. The Ig2 is really low and changes very little from Va=100V to 1kV. More importantly, the FU-50/GU-50 are relatively inexpensive and plentiful. A lot of them were made in the USSR and China during the cold war era. I read somewhere that those were designed for the comm gear used in the tanks and had very little success in commercial applications. I paid less than $3 a pop from Ukraine about 15 year ago. The going price for a NOS tube should be close to a SiC FET today. Well, any tube not designed for audio can be cheap these days. However, that wouldn't stop people from chasing after the Telefunken LS50 and the east-Germany SRS-552s, I guess 😉 Adapting those to the Carbon is surprisingly easy. I removed the SiC FETs and the 20k bias resistor, replaced the two 175k resistors with a 100V and a 130V 3W zener diode for G2 supply. The Ig2 is really small and the two tubes can share one set of the zener diodes. They drop 230V from GND and set Vg2 right at 150V, with about 22V left for the PZTA42 and the offset pot. The heaters are powered by a 12.6V filament trans with one side tied to B-. I could have tied the CT but there was very little hum to worry about. Guess what, the GU-50s work right out of the box. I didn't even need to adjust the balance and offset! The measured performance is pretty decent: Although the distortion is low, the FFT does show some higher order 'pentode nastiness'. I guess the reasons being The pentode is not super linear to begin with. The transconductance of the GU50 is about 1/10th of the SiC FET. The PZT42 has to work much harder and the global NFB is less effective. Something else worth looking into I'm not yet able to seriously listen to the sound, because I couldn't find another pair of tube sockets in my stash for the second channel 😂. If you want to know how it sounds, try it! The GU50 with 400V PSU comfortably beats the KGST (below) on the frequency response and the output swing: Next to try is to use the pentodes on the KGST, or should I call it KGSP then?
    2 points
  6. I dialled back the bias from 20mA to 17.2mA, installed a 562k resistor in parallel over one of the 175k resistors and achieved 24.8V bias voltage across the 20k resistor and Vce of the PZTA42 is 13.25V. Thanks to simmocon on this for the ground work for the 400V Carbon! The offsets on troubled board (after dialling down the bias) drift slowly down from around 5V. Still not sure why at 20mA bias I was getting no drift, I’ll leave that a mystery.
    1 point
  7. ^ That's my entire virtual record bag, archived. Normally only the changed files need to be copied, but part of the process of rebuilding my virtual DJ infrastructure changed the mtime on every single track in it. This M1 MBP doesn't have ethernet of course, so that transfer had to happen over WiFi. Related, I'm eyeing one of those CalDigit TB docks. Probability of me finally returning to the airwaves this coming Friday increasing.
    1 point
  8. well it was designed for 450v power. but really we are talking about only a couple db of difference. a minimum of -100db thd+noise. if you swap the transformer then you have to go with higher voltage rated power caps.
    1 point
  9. I only changed the LT1021 with the cheaper LT1236-10. The latter has the same performance as the LT1021 except the long-term stability which we don't need. Oh, and I used the DN2540 in TO-92 package for lower cost. Nothing is different from the original circuit electrically. If the output of the GRHV is low, chances are the passing element (SiC MOSFET) is not damaged. A series linear regulator such as the GRHV is probably the easiest circuit to troubleshoot. Jut need some electronics basics and a lot of patience...
    1 point
  10. Oh man, I've been putting off writing this one. I have 3 uncles, all on my mother's side. The youngest is a really good dude who has been tasked with dealing with the aftermath of the bad actions of other family members for his entire life. The oldest is an unimaginable piece of shit even by the standards of trash tier relatives. I would not micturate on him were he on fire. Sadly, he lives on at the age of 82, showing no signs of slowing down. My third uncle, the middle one, was born retarded. He spent some troubled times in the 1960s and 1970s in "state schools" which were horrible institutions in MA where all sorts of people with mental disabilities were dumped. In those places my uncle experienced horrors we shall never know. He was never verbal beforehand and was even less so after. From family stories I know he was attacked by aggressive "patients" (not really an appropriate term, but it's what they used) and was more or less defenseless. He'd show his trauma and pain by biting his own hands and the staff would notice the wounds. How long this went on I cannot say, but it was a time period measured in years. In the 1980s, he got out of the ellscape that the MA institutional system and into much more caring group homes. In the 1990s, he moved in with a family who were paid by the state to take care of him. Mercifully, they were a very caring group and took care of him quite well. Late last year the matriarch of that family contacted my youngest uncle (the good one) and said they could no longer really take care of my retarded uncle. That lead to a series bureaucratic headaches where my uncle eventually ended up back in MA institution. Fortunately they aren't as bad as they once were. Not too long after, my uncle contracted Covid. He recovered, but he was 63 years old and not in great shape. He was in and out of the hospital, most recently being treated for intestinal blockage. He returned to the institution and died hours later. His passing has been very hard on his surviving siblings (minus the asshole one, whose opinion to me on par with that one Mr. Putin.) I think for my uncle it was a mercy. What I observed of my uncle was that in spite of the horrors he experienced and witnessed, and his inability to communicate his suffering to anyone around him, he was an an amazingly sweet guy. His limited expressions showed shyness, curiosity, good nature, humor and a kindness I seldom see in us "normal" people. I tried to draw some inspiration from his kind spirit and find strength in his ability to rebound from trauma.
    0 points
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