HI,

I am about to build a DR103 clone. Going by pics and layout of the original but using some of Nik's parts.

First thing that catched my attention is the heatersupply. Why is Nik adding 100R resistors to ground (normally used with a tranny without center tap) while the tranny cleaarly has a center tap?

Just wondering

Ah! Good catch. Hadn't noticed the fact that there's  2 heatercircuits.

That explains it

if i'm looking at the layout properly, there is only one set of filament secondarys, center tapped as per normal, and one set of HT (High voltage) secondary taps center tapped as per usual. I attached an image to better explain...

I think tmac nailed it.  There is no center tap on the preamp heater currents. 

You may occasionally find a center-tapped filament current that also uses the 100 ohm resistors, that's for noise, the 100 ohm resister faux center tap actually gives a better reference to ground than a center tap.  How much better?  How much less noise? Probably not much, must people just use a center tap, but if I were building a hi-gain amp, I might consider it.

yup. I was looking at the 504 layout. Doh! My bad guys