Opened up this Philco, and what the.....??

[old_coot88]

I was guessing they were #47 bulbs. Just tested a couple of #47s. Each shows 7 ohms cold, rising to 10 ohms (due to heating from the VOM's 1.5V battery).

I don't have a #44 to test, but it would probably be around 4.2 ohms cold (due to higher current rating, .25A vs .15A).

Though maybe not "huge" but still a signifigant ESR figure if the bulb's in series with a 10 mf cap. But then you gotta figger in filament heating due to ripple, which will further increase resistance.

In any case, it seems like the more rational place to put a limiter/fuse would be directly in the B+ line coming off the rectifier.
Or two bulbs, one in each leg of the HV winding going to the rectifier plates.
Or, one bulb in the center-tap lead of the HV winding.

Just curious - where did you get the 1/10 ohm figure for the #44 bulb?