05-14-2016, 07:02 PM
(This post was last modified: 05-15-2016, 10:39 AM by Roman Ships.)
I have attached a schematic of my dual bias circuit.
I had read that if you bias tubes in pairs off of one bias supply that it can cause problems because it would unequally split the current. This makes sense in theory since the resistance to each branch would vary, but with such low current it seems like it wouldn't be an issue. Anyway, it seemed like I was reading that you should have separate bias supplies to bias tubes in pairs.
So I split after C16 and built identical bias circuits.
One feeds V5 and V6, the other V7 and V8.
I may have misspoke, C18 and C20 measure correctly. C20 is full B+ and C18 is about half.
C18 and C20 are wired in series. It may be hard to tell with my pictures. Below you will see which cap is which.
And the 100k R's are wired in parallel across each C20 and C18 per the schematic.
My "E" which comes off R51, and "D" which comes off between R52 and R51, both were reading full B+ with no tubes in. That was my main question, I figured they would drop once tubes were in. But tubes are blowing the fuse.
Hopefully these pictures clear it up and we can find the issue.
I had read that if you bias tubes in pairs off of one bias supply that it can cause problems because it would unequally split the current. This makes sense in theory since the resistance to each branch would vary, but with such low current it seems like it wouldn't be an issue. Anyway, it seemed like I was reading that you should have separate bias supplies to bias tubes in pairs.
So I split after C16 and built identical bias circuits.
One feeds V5 and V6, the other V7 and V8.
I may have misspoke, C18 and C20 measure correctly. C20 is full B+ and C18 is about half.
C18 and C20 are wired in series. It may be hard to tell with my pictures. Below you will see which cap is which.
And the 100k R's are wired in parallel across each C20 and C18 per the schematic.
My "E" which comes off R51, and "D" which comes off between R52 and R51, both were reading full B+ with no tubes in. That was my main question, I figured they would drop once tubes were in. But tubes are blowing the fuse.
Hopefully these pictures clear it up and we can find the issue.