voltage doubler caps size??

[swt]

Hi. i'm about to build an amp using a 220v/110v ( i live in south america). It'll be a single ended, really simple amp ala fender champ, so i'd like to use a regular transformer to do this. How do i calculate the value of caps?. I mean microfarads, and voltage requirement?. Thanks a lot for your help!

[Enzo]

I am unclear on your goals. What the mains are - 110 or 220 - is a separate issue from how you get your B+ out of it. Or are you looking to make an amp that will run on EITHER 110 or 220? Even then, the solution is simply to use a split primary power transformer with a switching arrangement. Then you can consider what to do on the secondary side. Unless you are stuck with only a couple transformer options, I would start with a power transformer that provided a high enough voltage to begin with. Voltage doublers are not all that complex, but why bother? Please tell me you are not planning to rectify the mains directly.

[swt]

fact is that i can't get anything for tube amps in here. And also, ordering from usa is really expensive for us. So as this is a small practice amp i'll build just for fun, i will use a common 220v to 110v and use a voltage doubler to get enough voltage for the tubes. If i use a full wave i'll only get 110v*1.414=155.4. But with a voltage doubler, it's going into the useful range. I know it's going to provide half the current, but as this is a 2 tubes project, it's cheap and tiny anyways. I'll use a 220v/6v for the filaments, and a small ot i ripped of an old tv for a 6bq5. Gibsons used 16uf and 450volts in their amps...but just wanna know if there's a way to get the math for this, or if i can use smaller ratings. Thanks a lot.

[Bruce / Mission Amps]

How much is too expensive?
I shipped a four or five pound box of vacuum tube amp parts to builder Brazil a while ago and it cost about $35.00 for the shipping/handling.

[soundmasterg]

I have a Conn organ amp that I'm using in a project that used a half wave voltage doubler in the power supply. It has three power amps in the one chassis. They share a common power transformer but each of the three pairs of power tubes have their own output transformer. Anyway, they used two 75uf 300v caps for the doubler. I changed to a full wave doubler using 4 diodes instead of the half wave using 2 diodes that they were using, and replaced the old caps with a couple 70uf 350v caps. I believe that the value of the caps when used in a doubler is just like if you connect them in series, so for the 70uf I have now, it ends up being the same as one 35uf cap, someone correct me if I'm wrong. The plate voltage went up about 20v under load compared to what it was as a half wave, and part of that could just be because I had new caps in there. B+ is now about 460v. I'd probably just find an amp you want to emulate as far as the first filter cap value, and then double that, and go with some appropriate voltage ratings on the caps.

greg

[R ski]

In theory they are usefull, however in power handling the size
of the capacitor has to large to keep up with current demands.
The 60 cycle line frequecy of your hydro, equates to 175 mfd.
at 1 amp.

The voltage should be 2.5 times higher than line voltage.

So when looking at 450 VDC 200 mfd they are can be hard find.

It is easier to get a power transformer to suit your needs.