3 - wire tube preamp power supply HELP!!!

[dschwartz]

Hi all!!

I´m starting to build a tube preamp, using the real mctube trick to get high voltage for B+ and low voltage for heaters..
The main idea for the power supply is to put two 220-12 volts (here in chile we use 220V) back to back in order to get 17VDC for the heaters (regulated at 12VDC, of course) and 320VDC for B+...but i have this design restrictions:

- The power supply must be on a separated enclosure..
- The power supply and the preamp are connected trough a 3-wire cable (PC power cable)
- The power supply box is small and all the filters won´t fit in there

My main problem now is how to feed the power to the preamp with only 3 cables..i think of this two options:



wich one will work best.. and  don´t kill me??
plz.. i know you know these one!

[John Lyons]

Neither of those I don't think.
 
                                                -------------------------12V heater
                                              /
   220vac-----------I        I------/-------I        I--------------AC high voltage
                          T1                        T2
   220vac-----------I        I-----/-------I        I--------------AC High Voltage
   GND----I                           /
              I                           -------------------------------12V heater
              I
              I----------------------------------------------------Ground to chassis


John

[stephanovitch]

Option 2 seems correct.
I use this configuration in my tube preamp.

[dschwartz]

John, thanks, but i only have 3 wires..i tried to find cables and connectors for more wires, but was impractical...

i think i´m going with option 2 like stephanovic said

i´ll separate the heaters gnd from B+ gnd at the filtering/regulation board....

[John Lyons]

So those diamonds in the graphic are bridge rectifiers right?
And your design won't have a chassis ground correct?


John

[bancika]

I used option 2 too for my hotbox-like pedal. It has speak-on 4 pole connector for gnd, 6V, 260V and 250V, works great. And separate power supply is not a restriction, maybe it's less practical to have two enclosures but:
a) you can build another different tube pedal without need for PS
b) with transformers far from circuit you'll get less hum

[dschwartz]

So those diamonds in the graphic are bridge rectifiers right?
And your design won't have a chassis ground correct?


John

yes, those diamonds are bridge rectifiers...

about grounding:
- the power supply enclosure will be grounded with AC outlet ground....
- The preamp enclosure will be grounded with the B+ ground
- the heaters will use different ground (from regulator)

should i better use the heater ground for shielding the preamp enclosure?

[bancika]

I connected all grounds together for my build and it's very quiet hum wise. Power supply joins safety ground, HV ground and heater ground. One ground line goes to preamp box and it's connected to tube pin 9 as heater ground, circuit ground and effect enclosure. Hope it helps.