SgtWookie - thanks, that makes much more sense about the diode! However, I have tried putting the schematic together, reversing the pin 5 diode as suggested, but am still getting 6VDC out of the transformer (with 6VDC in).

I have tried two transistors, a BC141 and a 2N5551, both with the same result. If I remove the transistor altogether, the result remains the same. My circuit is pictured below - same attempt from two different angles:

 

Did you remember to update the pins to match the datasheet for the transformer?

Here's the schematic with the corrected pin numbers and the diode flipped:

[eta] You really need to have a small cap on the output, with a 1MEG bleeder resistor. Without the capacitor, you'll only see rippled DC on the output. Without the resistor, it would take a LONG time for the capacitor to discharge.

 

Thank you for the revised schematic and all the other help.

The first time I built the circuit based on the original version of the kronjaeger schematic, I matched the transformer pinout with the photo of the transformer on his website. I remembered to put the diode in the right way. This, as I reported, gave me 6VDC out of the transformer.

I have tried again using your schematic, matching the pinout to the datasheet, rather than the photo. This time it gave me 0V out.

It may therefore be the oscillator. I have tried two NPN transistors, a BC141-10 and a 2N5551 - should these be OK? I've had a look for alternative transistor oscillator schematics online but while I've found a huge amount of reference material, I haven't been able to find a general purpose/generic schematic which I can try adapting. Do you know where I might find one or is kronjaeger's definitely OK (I'm a bit unconvinced after the diode)?

PatrackKing - I've tried your idea for achieving the same effect with LEDs, with some limited results, but will post in a separate thread.