[R-390] FM'ing with solid-stated PS

[Tim Shoppa]

I've heard testimony (I think it was first mentioned in an Electric Radio
from a decade ago but I've seen it repeated here and elsewhere)
that solid-stating the power supply, with a
200-ohm series resistor, can cause FM'ing of various receiver-internal
frequencies as the audio output goes up and down with strong signals
and modulates the B+.

My cursory inspection of the 26Z5W curves (see e.g.

 http://www.mif.pg.gda.pl/homepages/frank/sheets/087/2/26Z5W.pdf

) lead me to believe that a 26Z5W has an effective dynamic impedance
of 200 ohms.  (in particular for 100mA of load current the output drops
20V.)

So my gut feeling is that if there is any FM'ing due to a solid-state-with-
resistor PS mod, it's pretty much the same FM'ing that a PS with real
26Z5W's has.  All my PS's were solid-stated before I ever got them, and
I don't have any 26Z5W's in any event.

Did I make a mistake in my math?  By my reckoning this is a half-wave bridge
rectifier so at any moment only one rectifier is conducting, and there's no need
to double or half the 200 ohm impedance.  Are the tube curves not typical but
instead worst-case?  I read them as typical.

Tim.