I have to say that while it's the best I can do, it is a bit crude. But unless one has access to Time Lord technology, it's hard to get sophisticated ciruitry to fit into a sleder tube.
Since the orignial device, it has occurred to me that I could probably get more acoustical power from a better transformer. I used a standard Radio Shack xformer because 1) they're cheap and 2) they work okay. But if I had been a smarter fellow I would have made a special 'former that was round instead of square and with a higher turns ratio. The standard RS transformer was 1K: 8 ohms bcause you can get those anywhere-- at any Radio Shack or places like Mouser for a few bucks. I used to know the turns ratio but these days I've forgotten it, but I know it's not high.
A 'formr with say a 50:1 or even 100 :1 would put out a lot more voltage-- and more voltage means more power from the piezo ceramic. The only thing is that standard piezo discs are not made for very high voltages; maybe 60 volts max! Too much voltage and the ceramic cracks before you can blink an eye. But ya need more voltage to get more sound power. Might be a Catch-22 situation *but* some ceramic companies make high power ceramics such as PZT-8 that can take a higher voltage without cracking. Now here's the catch (and there's always
a ctach): PZT-8 doesn't work as well as PZT-5A, the ceramic used in standard piezo beepers, speakers, etc on a volt-to-volt basis. But the PZT-8 can take higher voltages so it kinda becomes a trade-off: you would need a lot more voltage to get the amount of power gotten from driving PZT-5A, but 5A will crack when driven from excessive voltages. Still, it *is* more power, but it might make the Screwdrivr a litle bit bigger using a round transformer.
Something to think about. ;-)