26-10-2016, 02:04 PM
I am now quite baffled by this tester. The test results do not see to be either consistent, or accurate. I decided to investigate.
With the test switch in the normal central position, the manual say that a standing 0.5 Volt ac negative charge is applied to the grid, and when the switch is pushed over to Mutual Conductance, a 0.5 Volt positive charge is applied to the grid. What on earth is a 0.5 Volt positive ac supply? considering the well-known fact that transformers produce ac only!
A close-up of the relevant part of the circuit is shown. LS3 is the 1 Volt secondary of the main transformer (centre-tapped) that supplies these two mysterious 0.5 Volt positive or negative charges. It even has - and + clearly shown on the ends!!!!
To further complicate matters, I put the meter between grid and cathode and found 1 Volt ac. This did not change when I pushed the switch across to MC.
Bob
With the test switch in the normal central position, the manual say that a standing 0.5 Volt ac negative charge is applied to the grid, and when the switch is pushed over to Mutual Conductance, a 0.5 Volt positive charge is applied to the grid. What on earth is a 0.5 Volt positive ac supply? considering the well-known fact that transformers produce ac only!
A close-up of the relevant part of the circuit is shown. LS3 is the 1 Volt secondary of the main transformer (centre-tapped) that supplies these two mysterious 0.5 Volt positive or negative charges. It even has - and + clearly shown on the ends!!!!
To further complicate matters, I put the meter between grid and cathode and found 1 Volt ac. This did not change when I pushed the switch across to MC.
Bob
