Looking for 50 Watt-ish power transformer with 12v tap

[fuzzjunkie]

Hey guys. I'm building another amp that will be 50 watts and have a little channel switching via relays. The last one I did had 5v relays and used the rectifier taps but they just couldn't quite come up to 5v after rectification. I would like to have a dedicated 12v besides the 6.3v heaters and run DC filaments on V1 (possibly all 4 preamp tubes) as well. I know Classictone made a project transformer like this but obviously that option is out

[martin manning]

You could use a voltage doubler circuit on the 5V tap. It would probably be fine with 12V relays and filaments with no regulator.

[fuzzjunkie]

Yeah, I gave that a whirl with the 5v just for a test but I wasn't sure what kind of current doublers can hold up to. No load voltage was 16v Didn't actually try it yet on the 5 volters. I ran standard 1n4001's and 100uf caps. Can you run an additional smoothing cap at the output or do you not need it?

[LOUDthud]

Yeah, I gave that a whirl with the 5v just for a test but I wasn't sure what kind of current doublers can hold up to. No load voltage was 16v Didn't actually try it yet on the 5 volters. I ran standard 1n4001's and 100uf caps. Can you run an additional smoothing cap at the output or do you not need it?

You need 470uF or 1000uF for doubler caps. There is a Voltage Doubler option in PSU Designer II. If you look around there is a version that runs as a web page if you are on a Mac.

[martin manning]

You'll need much larger caps. There will be no problem using a FW doubler with 2,200u caps with a 5V regulator for 5V relays. If you want DC heater current too, I'd go up to 10,000u, and see if the voltage is close enough to 12V at the regulator input for the V1 heater. The 5VAC winding should have at least 2A available, and you will need all of that.

[dorrisant]

This works 100% of the time with 5v and 6.3v taps. Double it (roughly 11-13v) and regulate to 8v. When you use a footswitch with LEDs, the LED/resistor combo will pull the voltage down. Omron G5V-2 works with this. The diode (D3) from output to input of the regulator is optional.

If you have a 12v tap then nix the doubler, rectify and regulate to 8v. I would bolt the regulator to the chassis with this setup.