2010-10-07 12:53 pm
Hi, I just starting a pre-amp project. (Project comming from Europe)
I have a problem to find a part or a way to get 330vdc.
I living Canada so... 120vac 60hz is the voltage.

Normaly, they take 240vac to a rectifier to get 330vdc.

Is there a way to do 120vac to 330vdc, there a way to 120vac to 240vac?

Any Idea?

The link of the drawing: Here


330 VDC

You could buy a tube amplifier transformer from or They typically will produce 400 VDC plus, then you put dropping resistors in (like 2000 ohm 1 watt) until you get the voltage you want in your circuit. Buy a phenolic header to install the resistors on at the same time as you buy the transformer. Be sure to buy resistors rated for 400 VDC, modern ones tend to be too short for tube voltages. You should buy the transformer that also has a winding to produce the filament voltage for the tube you are using. (Not on your link). This is typically 6 VAC, 12 VAC, or 5 VAC. You don't need much current for a preamp, so the smaller volt-amp transformers should be adequate.
Or you could use the original transformer from the kit, plus a 120-240 VAC transformer. I just opened up a dead PC-AT switcher power supply, it has the 240-120 VAC toroid transformer on a little separate board along with useful things like inrush limiters, overvoltage arresters and fuses, etc. The power supply is rated at 400 VA. Every hobbiest has several dead PC-AT power supplies lying around, right? Each of these has a 240-120 VAC toroid, although most of them have it installed on the main PCB and you have to trace out the lands on the PCB to find it. If the kit has no transformer, and if mains 240 VAC will produce 330VDC, transformer secondary 240 VAC should do the same and as a plus, be isolated from the mains if your house wiring is upside down. ( My previous residence was upside down, the big blade of the wall sockets was hot and so was the chassis of the TV I was trying to repair).
You will notice the schematic you reference has a 240 vac-240-vac isolation transformer on the B+ ( the common name of tube plate voltage) so that the ring of the RCA jacks going to and coming from the tube (not shown) is not floating 240VAC above earth potential. This is important, even if somebody told you it was okay to rectify the wall voltage directly.
Read the tube forum sticky thread about high voltage for newbies before attempting any of this. High voltages are deadly. Safety boilerplate for inhibition of your heir's lawyers if you mess up.
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2008-01-08 11:51 pm
You can almost always get the voltages you want by combining 2 transformers.


Here's an arrangement with 2 * 120/240 -> 6vAC transformers. Due to inefficiencies the voltages you get may not be quite as high as nominal, but you can overrate the transformers. Better to use a voltage higher than 6v for the intermediary, if you can run your heaters in series. Don't forget that supply voltages also vary, so at some times the output voltages may be higher than you anticipate. The range can be determined by asking your supplier and using this information in conjunction with the transformer datasheet which will tell you how the transformer output will vary with loading.

One 50VA + one 25VA will give you ~4A @6v and ~100mA @ 330v