As I promised last time, this month's column features the two-valve EF50 receiver which was originally published in the August 1955 issue of Practical Wireless. Some two years earlier, there was a very similar receiver published in the May 1953 issue of Wireless World. There's a high resolution image of the Wireless World circuit here. (Save it to disk as it's too big to see properly on-screen.) It seems there were twelve related articles covering simple t.r.f. and superhet receivers published in Wireless World. The unofficial 'series' began in March 1949, and closed with a car radio design in December 1956.
I received a lot of feedback when I mentioned the EF50 set last time. Thank you everyone who contacted me with information and stories.
One point I didn't mention last time concerning the KRC-A-2 inverter kit - as it stands, the kit will not work satisfactorily with NiCd or NiMH cells in place of the specified alkaline cells. The terminal voltage of the rechargeable cells is too low. An external power source can use rechargeable cells; both NiCd and NiMH cells are suitable as long as you use enough cells to give at least 9V (eight NiCd or NiMH cells would give 9.6V). Don't be tempted to try a 12V lead-acid battery without regulating the voltage to 9V first.
My esteemed Editor passed to me a letter written by fellow
Valve and Vintage author Chas. Miller.
Referring to my Power That Valved Portable
article in the December 2002 issue,
Chas. says that he is totally bemused as to why anyone would go
to all that trouble to power a valved portable set.
Why not use a 'D' cell and a stack of PP3-type batteries, he asks.
Well, for occasional use, I'm in full agreement. But if a receiver is used regularly, then rechargeable batteries have got to be both better long-term value, and more 'environmentally friendly'. But this misses the point.
Home electronics constructors don't always choose the simplest, most efficient - or even particularly sensible - way of doing things. People construct circuits for fun; to learn; to gain experience; maybe just to try something new. I knew an article about powering valved portable sets would have limited direct appeal, so I designed a collection of independent p.s.u. modules, each module having other potential uses.
I hoped everyone reading Power That Valved Portable would appreciate that the article was more than just a p.s.u. for a valved radio. The low dropout regulator, the switched-mode regulators, and the h.t. inverter were all meant to stimulate ideas for other power supply projects. After all, what knowledge would anyone gain, and where would be the fun, in simply wiring a few batteries together?
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