12v ac to dc --- again

[andrew]

Good evening all, I wired four 1N1007 diodes and a 10,000uf cap to convert ac to dc and I get a little over 16 volts. How can I bring it down to 12 volts? Thanks for any help.

[kwijabo]

what application are you shooting for? there's a couple ways.

first, just over 16 Vdc should be expected. 12VAC really means 12VACrms. so 12/0.707 = 16.9Vdc.

one option is to use a voltage divider.

another option is to feed the 16.9Vdc into a voltage regulator that has a regulated output of 12Vdc, but make sure it can handle 16Vdc as an input. check out the dumble side of things for a schematic. they use a regulator to supply the relays.

[ChrisM]

LM7812 and two caps.
Check the LM7812's datasheet for this application.

[andrew]

Thanks kwijabo but I'm trying not to order anything. Would a dropping resistor and another cap would help? What value should it be?

[Phil_S]

If you have no load on the circuit, then I submit you don't really know how much voltage you need to drop.

[John_P_WI]

Thanks kwijabo but I'm trying not to order anything. Would a dropping resistor and another cap would help? What value should it be?

+1 what Phil said.

When you know voltage with a load, you can add a few more diodes to each leg of the transformer. 1N4007 will drop 0.7 v each.

[Gaz]

Thanks kwijabo but I'm trying not to order anything.

You can find those regulators at Radio Shack. The other methods are pretty hack and won't give good, well, regulation.

[Firestorm]

Good evening all, I wired four 1N1007 diodes and a 10,000uf cap to convert ac to dc and I get a little over 16 volts. How can I bring it down to 12 volts? Thanks for any help.

Why?

No disrespect, but it matters what you want the 12V for.

[andrew]

I have a 12 vt tap and a 6 vt tap and I am using a 12sj7 and a 12sn7 in the preamp. I passed a Radioshack on the way from work and I bought a LM7812 for. Thanks for the help guys.

[Phil_S]

I have a 12 vt tap and a 6 vt tap and I am using a 12sj7 and a 12sn7 in the preamp. I passed a Radioshack on the way from work and I bought a LM7812 for. Thanks for the help guys.

I don't get it. Why not just use 12VAC?

[andrew]

That 12sj7 is noisy. I had a noisy 6sj7 in another build and converting the 6 vt ac to 6 vt dc fixed the promlem. Funny thing though the 12sn7 did not hum on ac. Thanks for the reply.

[renshen1957]

That 12sj7 is noisy. I had a noisy 6sj7 in another build and converting the 6 vt ac to 6 vt dc fixed the promlem. Funny thing though the 12sn7 did not hum on ac. Thanks for the reply.

Hi,

Have you tried DC Stand-off voltage on heater?

Best Regards,

Steve

[andrew]

I don't know what that is.

[ic-racer]

I don't know what that is.

Hook each side of the heaters to the ground with resistors. 120 ohm or 75 ohm on Dumbles.

[Firestorm]

I don't know what that is.

Hook each side of the heaters to the ground with resistors. 120 ohm or 75 ohm on Dumbles.

I think DC stand-off often also refers to the practice of tapping a well-filtered B+ node (like the screen supply), using a voltage divider to drop it down to 50-75V (often filtered) and hooking it to the heater center tap or the artificial tap.