Building a Tube Pre -- Best Way to use a 12VaC Walwart Power Supply???

[nicksorenson]

Anyone have a good 12V Power Supply idea for running a tube preamp?
thanks!
Nick

[tedmich]

there's another discussion around here, search for it.

Hoffman amps has a tiny toroid transformer which gives 240VDC from a 12VAC wall wart, there's also some PS designs for tubes in cars using 12VDC, the old Mctube uses two 12v transformers wired 120/12v-12v/120 to get ~150VDC for a 12AX7, lots of ways to do it, real HV (300VDC) is tricky to get from a wallwart, but the Ibanez Tube King Distortion Pedal manages pretty close

a backwards 12VAC/240VAC tranny powered by a 12VAC wall wart would give plenty for a 12ax7 and the 12VAC could run the heater (you'll always need 6.4-12.8 VAC/DC don't forget)

[teemuk]

12V for heaters, voltage multiplier for B+...?

[PRNDL]

I've looked into the 12VDC tubes and the general consensus is they are not suitable for microphone preamps, although they do make a decent guitar amp.

As to using a wall wart, the general issue seems to be power consumption. The microphone would have one tube, and the mic pre would have two (about 300 mA), for three in total. Although you could design a pre for non-tube mics, but then consider phantom power, which is used to power the transistors in a mic.

In general, mic preamps are carefully designed to minimize noise and interference, and it's difficult to find suitable low-noise low-microphonic tubes suitable for the a tube microphone at reasonable prices.

As for existing designs, check out these
http://www.tangible-technology.com/tubes/1566/1566.html
Gyraf Audio - G9 DIY
Dual Tube Microphone Preamp

The second issue, is why bother when you can buy an ART Tube MP for about $50