CTH Setup


Inital Setup

Follow this procedure to bring up your CTH. You will need a digitial multimeter. If something goes wrong, disconnect the power connections immediately. You need to be reasonably skilled at using a DVM and accessing test points on a PCB. Use the Wiring Pad finder to locate the pads and pin locations on the various devices.

Board Pad Locations

CTH Wiring Pads (300dpi PNG) CTH Wiring Pads (600dpi PNG)

Staged Start Up

All voltages are measured with respect to SG unless otherwise noted.

Insert all opamps be DO NOT insert the tube.

WARNING - 100VDC is significant high voltage. Every precaution for handling HV should be exercised.

Plug in the wallwart and wait for at least 2 minutes. If there is smoke turn of the amp immediately, but if not wait. The indicator should go from red to green. Whether it does or doesn't, check these voltages anyway.

  • Measure between OG and SG. This should be very close to 12V. If it's not there might be a problem with the TLE2426 or with one of the devices in the rail splitter.
  • If the OG measurment is good, measure OL and OR. They should also be very close to the voltage at OG. If they are the buffers and splitter are working.
  • If OL and OR are not close to OG (>50mV), then either the buffer opamp is not working or one or more of the buffer BJTs are dead or the wrong hfe class.
  • If OL and OR are close to OG the green light should be on. If it is not there is a problem in the ε12 or the LED RTL logic.
  • Power off and let the PS bleed down.
  • Set the heater switch for the heater voltage of the tube you want to insert.
  • Insert the tube and turn on the amp again.
  • Look for smoke. If there isn't any then . . .
  • Measure TB+. It should be between 95V and 105V.
  • If TB+ is ok, measure pins 1 and 6 of the tube socket. These should be approximately 80V. If they are, and if the previous measurments are correct, then your amp is ready to go.
  • If TB+ is wrong there is a problem in the HV multiplier. Check diode and cap orientations.
  • If TB+ is good but pins 1 and 6 are far from 80V the tube opamps may be bad or a component value may be wrong.
  • If everything in the tube circuit tests good but the plate voltages are still far off, the tube is bad.