gareth wrote:
These LED replacements for 240V mains lamps; if one were to
open them, would one find a high voltage regulator suitable for
some of our valve experiments and repairs?

You might find a little constant current supply, but my guess is that
you'd just find a big dropping resistor. That configuration would
result in most of the power being wasted as heat, but it would still
produce less heat than an incandescent and be brighter.

If you want a high voltage regulator, a TIP50 transistor and a high
voltage zener (or a string of low voltage zeners) will fix you right
up. The TIP50 is comparatively easy to damage, but if you don't hook
it up backwards or something it will be very, very reliable. Not
expensive.

Think of the TIP50 as a 5080 replacement with a lot more gain and
better transconductance in the bargain.

If you want a high voltage switcher, on the other hand, look at the
Linear Technology chips intended for LCD backlight inverters. There
are some great Jim Williams applications notes.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."