DC filliment with separate transformer, ground reference?

[89Custom]

If you were to add a filament transformer to an amp and wanted to run DC filaments, should the circuit be floating, or connected to ground via a capacitor or balancing resistors? The transformer in question does not have a center tap, if that makes any difference.

[Axekisser]

In my Carvin Nomad and on my Valve Jr It goes from the AC Xfrmr to the bridge rectifier to two 100 ohm resistors (one on each leg of the + and - of the rectifier) with the other ends of the 100 ohm resistors tied together and grounded. Put (2) 2200 uf caps across the rectifier( again + and -) and the tube filaments go across the same + and - legs of the rectifier.

Use 1% resistors and make sure the caps and rectifier (I assume you're using a solid state rectifier) are appropriate for the filament voltages (usually 6-6.3 volts).

Here's a link to the Carvin schematic. Pull the PDF for the Vintage 50 and you'll find the DC filament circuit section in the middle of page 1.

Best of luck!
http://www.carvinmuseum.com/techdocs.html

[89Custom]

Thanks:BEER

I notice the Marshall studio 15 is the same way.

[donnyjaguar]

Generally you want to attach the - contact to chassis ground or float the collective circuit such that it is placed betwixt your two + and - extreme cathode voltages. If you're running a tubes in fixed bias this would be approximately the cathode voltage of your phase splitter divided by 2. I can explain why if required.