bridge rectifier bias question

[rhinson]

the transformer in this schematic has it's own bias winding apart from the hv sec winding-----you can either make the old standard half wave circuit, a bridge circuit, or a voltage doubler even and get the neg. voltage supply you need. we were under the impression the trannie you had had no bias winding and that you were taking it off the hv sec winding. if that's the case then you will need a blocking cap coming off the winding if you your going to roll your own from the hv sec winding. rh

[andrew]

I tried the Sundown plan but for some reason it kept blowing fuses. I was intimidated with the bias tap schematic but managed to make it work. The voltages are high for an Express but is there any harm in running it this high? I have a Zener that will bring it down 30vts but would it make that much of a difference?

[rhinson]

you're not quite understanding here. either your power transformer has it's own bias winding or it doesn't. if it does, there are several ways to use that winding to get a neg. voltage supply (3 of which are listed above)-----the sundown method is not one of them. that circuit is for the case when your hv sec winding does not have a ct, thus meaning you have to use a bridge rect. setup to get your b+ supply. you have to use a blocking cap off the hv sec ac let-----you can build the rest of the bias circuit a lot of ways/styles but you need the blocking cap or it won't work properly. rh