Alan Douglas adouglasatgis.net wrote:

Any tester made after, say, 1950 will probably use a lower grid
signal than 5V. The lower the better, for low-bias tubes like the
12AX7.

Two more questions:

1) Is there a risk of damaging a 12AX7 by testing it in the I-177?

2) Is there an easy way to lower the voltage of the grid signal in an I-177?

Thanks.