Curing the power supply blues…

Original FRG-7700 power supply board.

Like most (but not all!) things, there's a lot of info about Yaesu SWL/ham gear on the internet. For starters, there's the Fox Tango International Yaesu Users Group (ye olde 80's style design!) including Wim Penders' Yaesu FRG-7700 Survival Guide, and the FRG-7700 specific Yahoo FRG-7700 users group. I'm sure you can find more…

I fully expected to find an improved power supply design somewhere, and was little surprised when I didn't. Not that it's an especially difficult thing to design, but simply because these sets are still quite popular (check out the ridiculous prices on eBay!), are now getting on into respectable middle-age, and many would be owned by people unfamiliar with electronics. The only example I could find is Wim's design in his Survival Guide - and it's deliberately more of an update/copy of the original design, with the 13.5V rail still unregulated but a LM317 regulator IC replacing the zener/Q02/Q03 discrete regulator of the original. I'm not sure why there's no other designs for improved supplies - maybe it's as simple as most sets are in the USA with 110/120VAC mains or, like Wim, are in Europe with 220V mains? Perhaps the transformer's primary voltage select taps are better suited to those voltages rather than Australia's 240VAC, resulting in the 13.5V rail being somewhere near what it should be?