Device for matching Vacuum Tubes

If two or more tubes operate in push-pull circuits in a tube amplifier, the tubes should have similar, if not the same, operating parameters.

I built this meter to statically compare two electron tubes. The function can be considered as a bridge circuit in which two bridge elements are fixed resistors and two bridge elements form the electron tubes to be measured. During the test, the same (adjustable) voltage is applied to the grids of the two vacuum tubes. In the bridge branch, any deviations in the two tubes can then be read.

The following operating parameters can be set:

• Anode voltage: 310V, 620V or 930V (x1, x2, x3)
• Anode resistances: 1k or 4k3 (max. 50W)
• Cathode resistors: 1Ohm or 10Ohm (used for current measurement)
• Grid voltage: 0Volt to -125Volt (intern / extern)
• Heating voltage: 6.3Volt or 12.6Volt

 

The connections for the tubes are located on built-in sockets and all parameters (voltage at the anodes, current through the tube, grid control voltage) are displayed via LCD displays.

 

The deflection sensitivity of the measuring device (with center position) for the bridge current can be adjusted.

The grid voltage can also be introduced via an external source (intern / extern) for remote control operation. The measured values for anode current and anode voltage are also shown at the same plug connection (back). This means that the device can also digitally record tube characteristics using an appropriate interface and PC software.