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JoaMat last won the day on November 9 2019

JoaMat had the most liked content!

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About JoaMat

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  • Birthday 12/26/1955

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  1. JoaMat

    What Are You Building Today

    Thank you, Michael. Working on a layout... we'll see what happens.
  2. JoaMat

    What Are You Building Today

    A gentleman told me about the electrostatic amplifier Sirrah designed by Andreas Rauenbuehler. See http://www.high-amp.de/ . Inspired by Sirrah I draw this sketch… …20 mA per channel. Accompanied with small GRHV regulators and 50VA transformer - could be built in a small box for the bedside table? maybe it won't work at all.
  3. JoaMat

    What are you listening to Part the Third

    I like this “beginner”, his first album? Wow! Thank you. P.S. His touring …
  4. JoaMat

    What are you listening to Part the Third

    Didn’t found it on streamers but some kind person in Germany sold me this CD. Thanks! Worth every pfennig.
  5. JoaMat

    DIY mini T2 Build Thread

    Thanks a lot, mwl168 and jamesmking. Your information indicates – as I interpreter it - the voltage differential is in the region 30 – 40 volts. Good to know.
  6. JoaMat

    DIY mini T2 Build Thread

    84,3 VA. Voltage * current of each winding. Then add VA of all windings. Done. Reservation for errors!
  7. JoaMat

    DIY mini T2 Build Thread

    Regarding GRHV regulators. What’s the minimum voltage differential/headroom for the GRHV to work properly?
  8. JoaMat

    DIY mini T2 Build Thread

    Well, I use some old DIY T2 supplies for all my amplifiers. For LV and filament transformer I have the following windings 15V + 15V / 0.5A (center tap) 6.3V / 4A 6.3V / 4A 6.3V / 1.5A 6.3V / 1.5A You don’t want to use same winding for small and output tubes. Separate windings for channels. So total four filament windings. Demands for HV is 60mA for output stage and 20mA for input. With +220V supply you I suggest 195V/0,06A 320V/0.18A 365V/0.18A \\135VA Without +220V supply, feeding input positive via 20k power resistor, I suggest 320V/0.24A 365V/0.18A \\143VA Calculations are based on 50V headroom and current factor of three (some builders may want another factor). Reservation for errors!
  9. Lazy engineer/designer
  10. JoaMat

    DIY mini T2 Build Thread

    Frankly I expected OP27 to fail sooner or later. I’ve had several OP27 failures, only the offset servo – no balance servo failure so far. I hope that the OPA197 is more robust. I’ll use OPA197 from now in new builds… as long as they work properly…
  11. JoaMat

    DIY mini T2 Build Thread

    So – now it has failed (couple of days ago), both outputs at +HV. First I put a 650R resistor cross Q10 collector/emitter which brought offset voltage down to +60V increasing to about +90V when warm. Changed the failed OP27 to OPA197 today and now it’s working again.
  12. JoaMat

    KT77 application in Stax amps

    Four Gold Lion KT77 in a mini T2. G3 connected to plate on PCB. It rocks Beautiful!
  13. JoaMat

    KT77 application in Stax amps

    If interested in the story of good old tubes, I recommend Guide to the EL34/6CA7 by Pasquale Russo. Also some information on the KT77. 365 pages of interesting stuff.
  14. JoaMat

    KT77 application in Stax amps

    Not sure which one of all Kevin’s designs the “all tube Grounded Grid” is. But in mid-2017 both members congo5 and MattN have built what seems to be something similar to Kevin’s KGSSHV-TUBE- SANDWICH – ECC88 input and EL34 output tubes. Ref. https://www.head-case.org/forums/topic/12949-stax-t8000-clone-well-sorta/
  15. JoaMat

    Happy New Year!

    Happy New Year!!!