I had a working 6v6 plexi build for the past year, and enjoyed it much.
In order to mess with it a bit, I thought I'd tangle with the bias and try out a cathode bias.
It didn't work, for some reason, and I decided to revert it back to fixed bias.
Problem is, all of a sudden the volume is very very low (barwly noticeable at Max settings), and when I measured the bias I noticed it reads 100v (rather than -30 -40), and the joint between the 220k resistor to the reverse diode of the bias circuit reads 400vac, while the transformer is only 330-0-330.
So I detached joints one at a time, and got to the conclusion - when nothing connected to it, grid1 is 350v to relative ground. What the heck?
Both tubes do it.. And they worked perfectly an hour ago.
What to do?
In order to mess with it a bit, I thought I'd tangle with the bias and try out a cathode bias.
It didn't work, for some reason, and I decided to revert it back to fixed bias.
Problem is, all of a sudden the volume is very very low (barwly noticeable at Max settings), and when I measured the bias I noticed it reads 100v (rather than -30 -40), and the joint between the 220k resistor to the reverse diode of the bias circuit reads 400vac, while the transformer is only 330-0-330.
So I detached joints one at a time, and got to the conclusion - when nothing connected to it, grid1 is 350v to relative ground. What the heck?
Both tubes do it.. And they worked perfectly an hour ago.
What to do?
> try out a cathode bias.
Very unwise with 6V6 at 433V(!) and any likely load.
> the joint between the 220k resistor to the reverse diode of the bias circuit reads 400vac, while the transformer is only 330-0-330.
Yes. There is some DC on the other side. Many "AC" meters will read AC+DC together.
> when nothing connected to it, grid1 is 350v to relative ground.
"Nothing connected to it" is NOT a normal condition for G1. You are really more interested in what it is connected TO.
Can you get around Negative 50V on your 47u bias cap?
Very unwise with 6V6 at 433V(!) and any likely load.
> the joint between the 220k resistor to the reverse diode of the bias circuit reads 400vac, while the transformer is only 330-0-330.
Yes. There is some DC on the other side. Many "AC" meters will read AC+DC together.
> when nothing connected to it, grid1 is 350v to relative ground.
"Nothing connected to it" is NOT a normal condition for G1. You are really more interested in what it is connected TO.
Can you get around Negative 50V on your 47u bias cap?
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