terryS wrote:

Unfortuantely somebody 'sold' his parents (the youngsters Christmas
gift) at an excessive price a B and K Dynaquik 500, tube tester which
is not only somewhat used and very mouldy but also doesn't work!

What doesn't it do?

Hit the case with Lysol and get the mold off. Then apply power, and
tell me what happens. Can you center the meter? If you put a tube
in, does the filament light up? Is the series light bulb good or has
it gone open?

All transconductance testers are basically a power supply, some series
and shunt resistors, and a meter. Plus a lot of switching. If nothing
works, it's in the power supply.
--scott

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