Jig is correct. Some 6922/6DJ8 tubes are more prone to microphonics than others. If you have some spares to swap, try that. Sometimes the use of tube dampers can help with that. Herbies Audio Labs HAL-O tube dampers are very good at cutting down microphonics.
The high pitched "ringing" you hear from these tubes might be from microphonics being caused by vibrations in the tube.
The high pitched "ringing" you hear from these tubes might be from microphonics being caused by vibrations in the tube.