[Arran]

The watch batteries work but the polarity is the opposite of one of those vintage Mallory bias cells. With the style I run into in Rogers sets, the kind with the cylinder that fits the domed side, the cylinder is negative, and the spring contact is positive, so you have to rewire them to use the modern watch batteries which have the case as positive. I don't think the availability of one type of resistor or another had much to do with why bias cells were used, I've never seen a radio older then 1936 that had them, the newest set I have seen with them was a Canadian Marconi set from 1941. They claimed that it was to simplify the power supply, but since the usual method was to place a resistor, and cap, in series between the cathode of the tube, and ground the parts count would be negligible. I'm guessing that it was either to create a service item that would create extra business for repair shops (keep in mind that other then electrolytic caps the paper caps seldom needed replacement when these sets were under 10 years old), or that it was a scheme to avoid paying patent royalties. Weird that a Stromberg would use one, all the ones I have encountered do not, and Stromberg didn't care about patent royaties, they just paid them.
Ifg the set has all original caps I would restuff the paper ones, and the cans on top, there seems to be more then enough room for everything under that chassis.
Regards

Arran