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It is for the negative voltage for a fixed bias supply. I have not been able to find a small one that would easily fit inside a chassis. thanks for the help
you can get any of the antek 10VA toroids which have dual 115V winidngs and use them as a 1:1. Another possibility is one of the triad or signal "flat pack" transformers which also have dual 120V windings. If one wants to get creative with either they can simply put the dual secondaries in series with the dual primaries to reduce the overall flux on the core which should be a plus for this application.
by this "If one wants to get creative with either they can simply put the dual secondaries in series with the dual primaries to reduce the overall flux on the core which should be a plus for this application."
assume a 120+120:12+12 transformer.
also assuming 4 discrete windings it can be configured as a 120+12:120+12 which is a 132:132. Since 132:132 is 1:1 it can be used as a 120:120 and placing 120V on a winding that can handle 132V winding will result in a ruduced flux on the core which means less radiated magnetic field. Getting even more industrious you could also use a single 120V winding as the primary and use the other three windings in series for the secondary to get a 120:144 transformer if you need a bit more voltage and then placing 120V across the 144 winding will get you about 100V.
For the flat pack transformers I mentioned each winding is on its own discrete bobbin section so there will be isolation from each section to another and this design also limits the capacitive coupling transmitted between windings. Just as this design would make a really crappy output transformer it does nicely as a limited bandwidth power transformer.
Now, the second thing how easily mounted are any of these ? With the generic open frame trans i only need 2 holes and 2 screws. I really have not used toroids or the other one. Also have you tried using a toroid as you mentioned for a negative voltage source? thanks, Dak
the smaller "flat pack" transformers are PCB mount but they typically also have two holes in the lams that could be used along with standoffs. The toroids just take a single bolt through the center. You sorta need them in hand to come up with a plan but either should be workable.
I use toroids a lot for my phono stuff but am moving toward the flat/pack type design for future experiments.
both mouser and digi-key have them.
Triad Flat Pack
Bel / Signal Flathead
for your application since you are looking for just a voltage source, I would think the smallest ones should suffice.
Do you really need 120 VRMS? A link to a tiny Amveco toroid with 2X 22 VRMS secondaries is provided below. Wire the secondaries in series to get 44 VRMS. "Full wave" voltage double the 44 VRMS to obtain the bias (C-) rail.
Thanks for the tip Eli. The new trans will replace a reverse installed 6.3vac filament trans which would output , 120vac. So, everything is already dialed in and working but i want to replace it to free up the filament circuit for some needed DC biasing. I found out, the hard way, that you can't do both at once. cheers.
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