Looking for batteries for a portable

[Jeffhs]

Originally Posted by YamahaFreak

I scored a Motorola model 5P31A for a whole 3 bucks. It's a great sounding little radio, and I would like to find some batteries for it if i could. It uses an Eveready no. 479 90-volt A battery and a no. 707 7.5-volt B battery. I've tried eBay and Google with no luck. Are there any places I can still get these, or am I going to have to cram nine 9-volts in there???

The radio:

http://cgi.ebay.com/ws/eBayISAPI.dll...MEWN:IT&ih=006

I think you have the type numbers of the two batteries transposed. Ninety volts is far too much for the filament supply, and the radio could not possibly work with only 7.5 volts B+ on the plates of the tubes.

BTW: I have heard of schemes such as you mention (connecting nine or ten nine-volt transistor batteries in series) to replace a 90-volt B battery in old tube-powered battery/AC portable radios when the normal 90- or 67.5-volt pack is unavailable. The improvised 90-volt battery will last quite a while, as the tubes in these old battery portables didn't draw much plate current. However, I wouldn't use anything other than alkaline batteries (nothing smaller than D cells) to replace the A (filament supply) battery, as the filaments in all the old 1- and 3-volt battery-radio tubes drew an awful lot of current; so much, in fact, that a four-tube battery radio (for example) would eat up a set of carbon-zinc batteries in a matter of minutes.