single transistor projects?

Thing is, peimary batteries go flat and need replacing, often at the most inconvienet possible time. For a homebrew project I'd rather wire up som 9V batteries that I can get just about anywhere than have to order a special battery from across the Pond. Sure. There are companies who sell those in the UK too (either as kits, or assembled), there was a project to make one in, I think, Elektor. Most of the time these run off a low voltage (rechargeable?) battery that runs the valve filaments too. The power pack is a simple transistor osciallator + transformer kind of thing to generate the 90V or so HT. The advantage of that is that the radio (or whatever) remains battery-powered and thus portable. But again, for a homebrew project that's going to be used at your bench only, a mains supply is probably simpler Indeed. There were some sets of articles in, for example, Practical Wireless magaxine in the 1950's that were intended to act as an electronics course. To save money, the mains transformer only provided the heater supply, the HT+ (B+) was obtained by connected mains neutral to the metal chasiss and a half-wave rectifier to mains live. Some of the projects in said 'course' used headphones. I would think a fairly small error in construction, or insulation breakdown, could turn that into a very effecitve electric chair. No thanks! Personally, if I'm going to mess about with valves and their attendant high voltages, I am certainly going to use a double-wound mains transformer. -tony