Ungrounding Paramount PT-4 6.3V Center Tap

[AudioDave]

I am toying with the idea of converting to DC filaments on my Paramount 5670 driver tubes.  I previously had purchased a couple of Ultra Low Noise regulated filament supply modules from DIY Hifi Supply and would like to use those,  however they utilize a full wave bridge for rectification so will need an ungrounded center tap on the PT-4 6.3V secondary.   My question is, which lug on the PT-4 is the 6.3V CT?   I guess my second question is, do you think this is a good idea or not worth the trouble?
Thanks!
Dave

[Paul Birkeland]

The AC heating of the 5670 is, in our experience, not a significant source of noise.  Do your Paramounts hum audibly now? 

[AudioDave]

No,  not much hum at all!  Just in the mood to tweak and had the filament modules laying around.  Sounds like I should probably save them for another project!
Thanks for the feedback!
Dave

[Paul Birkeland]

The key difference is between filament (right smack dab in the signal path) and heater (pretty well insulated from the signal path).  The directly heated output tubes in the Paramount benefit from DC heating (which they get), but the driver tubes do not. 

[Paul Joppa]

The 6.3v winding CT is the center trace of the three parallel traces at the front of the PSU board, just left of center. It must be at AC ground, because it serves as a shield for the 300B/2A3 filament winding, preventing power line noise and high voltage rectifier noise from entering the filaments. In the stock design, it is grounded by the shield of the STP, at T17.

[AudioDave]

Thanks Paul !