I finished wiring the voltage loops for all the regular connections from the circuit board. After very carefully checking every connection with a continuity tester, I discovered that when I swapped out the original selector switch for a new one yesterday, I miswired the filament connections. With that fixed, it was time to run a trace on sample tube, a 6AU6.
|Leveraged tester that has become the curve tracer|
- filament side A
- filament side B
- control grid
- screen grid
|Marked controls and active sockets only|
The normal mode of operation is for the circuit board to build up the target voltages in the screen and anode reservoir capacitors, but only connect those to the screen and anode pins for milliseconds at a time while making measurements. Certain unusual measurement situations may require a steady voltage, not a short burst, which is the purpose of positions 10 and 11.
The boost converters can't supply more than 3ma steadily, so this connection to continuous screen and/or anode reservoirs will only work for low current applications. The archetypical case for using the reservoir voltage is to test magic eye tubes. This will not be a frequent mode for me, in fact I may never use it, but the wiring should be in place.