Impedance Switch Ground

[nflrage]

First Post!!! I built a MoJo Britt 800 and am currently in the pre-startup testing phase making sure there is NOTHING out of place. My question is, when using my VOM, I ground negative to chassis and probe the 4/8/16 impedance poles on the back of the switch I receive a tone. This obviously means it is grounded somewhere...is this normal? Attached are the docs how it is currently built.

Impedance Selector.PNG

[sluckey]

That's normal.

[nflrage]

So I can assume it is grounding through the OT?

[martin manning]

So I can assume it is grounding through the OT?

Correct. The secondary windings have relatively few turns, and only a couple of ohms DC resistance. Set your meter to measure ohms and check the resistance to ground from each power supply node (HV filter capacitor positive terminals, bias supply filter negative terminals). You should see at a minimum some tens of thousands of ohms.

[nflrage]

Thank you guys...I appreciate the quick assist!

[bepone]

if you are using feedback from secondary to the PI tube, then is grounded on the wrong point..OPT gnd belongs to the return wire of NFB; they need to travel together to the mixing point (presence pot) and there need to be grounded (actually gnd from the capacitor supplying the PI tube also need to go there too).

if you are not using NFB then OPT gnd point is fine.