Strange switch behaviour

[Randall]

I'm looking at a Dr Z amp that runs four 6V6s, and has a Hi/Lo switch that switches a grid on each pair from either signal or 100K to ground. It was making a fair bit of noise in the Hi power position, so I got some deoxit in there. While I was investigating, I found the center tab measured a short to one side of the switch in one position, and 190K ohms to the same point in the other position. This true for all four cases, 190K to either side when in the off position, for both switches. Just to be sure I lifted the most accessable connection to the center lug, and the same is true. I realize switches go bad, but the same resistance in all four cases?

Before I replace this switch, is there such a thing as a resistive DPDT switch? So strange.

[Jazz P Bass]

It seems to me that what you are reading is two grid resistors in series.

[Randall]

"It seems to me that what you are reading is two grid resistors in series."

No, I really don't thinks so. The grid resistors are 1.2K, and I don't see a path for any series connection. Plus, the center wiper, or common, whatever it is called, is disconected. Another thing I just realized, the two outside terminals of the switch measure 189K and 190K across each of them respectively.

[The Dude]

Do you have a schematic so we can see what's going on in the circuit?

[Dave H]

Perhaps it's like this?

[g1]

Might as well just disconnect completely and measure.

[Enzo]

It seems to me that what you are reading is two grid resistors in series.

No, I really don't thinks so. The grid resistors are 1.2K,

I THINK he meant two of the 100k resistors in series. As in perhaps the grid return resistors. I could imagine two resistors to ground, and when the switch opens measuring resistor to resistor yields 200k, 190k close enough, the fact that they go to ground in the middle doesn't change that. Possible?

[Dave H]

This would make it 190k

[Randall]

It is wired like the one in post #5 if you change the leftmost 100K to 90K. It's a Dr Z so no schematic. I was reluctant to do much disconnecting given the immaculate wiring and red marker dots on every solder point, but once I did the switch acted normally, so it seems I actually have no problem here.

I still really am not seeing why I get 190K across the switch with it all connected.

edit: Oh wait, light bulb goes off, now I get it. The 100K and 90K are connected at ground putting them in series, but being grounded really doesn't have anything to do with it. DOH.

[dmeek]

This may be the schematic (reverse engineered). I don't remember where I found it.

https://music-electronics-forum.com/...1&d=1578431216