Built a board. 4x INA128 instrumentation amp input plus 2X single-ended inputs, all powered on 24V.

INA128 can run up to 36V, LM358 up to 32V. SRPP offset voltages are around 45V or higher, so maybe with the divide-by-two inputs it would be better run on 28V or even 30V.

• Design: ​http://edf.bu.edu/svn/edf/EricHome/TubeAmp/BiasMon/bias/
• Schematic: ​http://edf.bu.edu/svn/edf/EricHome/TubeAmp/BiasMon/bias/tags/RevA/bias.pdf

11/8/20

Stuffed board, trying to test. Completely screwed up the programming connector. It's a 2mm pitch numbered wrong. Managed to wedge in a 2x3 header, can maybe fix the pinout with a knife.

  MISO (18) -- 1   2 -- VCC
   SCK (19) -- 3   4 -- (17) MOSI
  nRST (1)  -- 5   6 -- GND

Now I can at least download blinky light firmware :)

Box:

• Hammond 1590BB (metal) ​https://www.hammfg.com/part/1590BB
• Hammond 1591B. ​https://www.hammfg.com/electronics/small-case/plastic/1591t
  • Would require board < 2.89" wide board

INAs would measure the four bias voltages. Additional channels would measure the DC offset from GND of the cathode circuits on each side.