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Saturday, June 6, 2015

Field Coil Power Supply with Mercury Vapour Tubes


The mercury vapour madness continues. Here is a power supply for RCA 1443 midrange drivers. It uses 816 mercury vapour rectifiers in a bridge rectification arrangement with two 6CG3 TV Dampers.

The RCA1443 has a high voltage field coil which requires 115 VDC at 170mA current. This spec makes a tube rectified supply feasible. Especially when the drivers for left and right are fed in series, then the voltage doubles to 230V.

Smoothing of the voltage is done in a purely passive fashion using chokes and oil caps.

Digital displays have been added to monitor voltage and current.

Output voltage can be adjusted in several steps to account for variations in line voltage and actual current draw from the drivers.

With a current of 170mA the blue glow of the 816 tubes is clearly visible at daylight:

And becomes more visible in the evening ...

... or at night

The 6CG3 tubes provide a nice slow warm up as can be seen in this video clip:

Here seen from another angle:

Best regards



  1. Hi Thomas,
    Are the (indirectly heated) damper diodes used in conjunction with the 816s, in order to provide a slow warm-up for the mercury diodes?
    Cheers, Owen

  2. Hi Thomas,
    You obviously like valves that glow brightly in the night, but I have never seen you use voltage stabilising valves. What do you have against them?

    Best regards,

  3. Hi Bo,
    If I haven't used yet, it doesn't mean that I have something against it.
    Voltage stabiliser tubes don't really match with my circuits

    Best regards


  4. A noob question: what are the advantages of tubed field coil power supplies?

    1. As with many things in audio you will get different opinions about this. I would say the advantages are similar as when using tubed power supplies for an amplifier


    2. I have zero experience with field coils, I didn't know the field coil power supply could affect the sound on that way. Thanks!