On 08 Aug 2007 09:30:25 GMT, John Phillips
wrote:

On 2007-08-08, Don Pearce wrote:
On Wed, 08 Aug 2007 07:58:46 +0100, Nick Gorham
wrote:
That particular GM70 is still going strong, the old USR certainly knew
how to make robust triodes.

There is a lot of ventilation in the base for that very reason, the
convection from below the valve carries a lot of the (non radiated) heat
away from the amp, the TX's near get warm, but not worryingly so.

In my earliest work days I designed colour TVs. We had an X-Ray
detector permanently covering the bench, because if the line output
valve got a few too many volts, and a bit too much current, its anode
would start to glow red, and X-Rays would come flooding out.

In days long gone, articles in Scientific American (from my school library
stock) told you how to do interesting but potentially dangerous things.

One showed how to take an old triode, cover the outside of the envelope
with thin aluminium foil, common all of the pins (possibly leaving
the filament still powered? - it's a long time ago) and apply a few kV
across it.

Apparently, suitably energetic electrons striking the silicon in the
envelope glass produced X-rays and there were examples including X-rayed
fish (non-filleted, of course).

I really wouldn't be sitting close to this thing for ten minutes if I
were you.

For which reason Scientific American is now rather boring. I sometimes
wish we could still see articles on making 2-metre-long zinc powder and
sulfur (sic) powered rockets that could reach 1,000 metres, etc.

And don't forget the instructions for making Tesla coils. Happy days.

d

--
Pearce Consulting
http://www.pearce.uk.com