"N Cook" hath wroth:

In a valve Dansette Bermuda of early 60s
Been in a loft for years.
The mains wiring is perished and other wiring looks dodgy so testing some
things cold first.
Using 9V battery and 300 ohm dropper shows near enough 9V over the
rectifier, how high V do you have to go with a good one to check it ?

Dunno.

Are there safety grounds anyway for changing to a 1N4007 or so ?

Yes. The original selenium rectifier has a rather substantial forward
voltage drop. The design of the filters and the rest of the receiver
take this into consideration. When you replace it with a 1N4007, the
forward voltage drop will be MUCH less. Chances are good that you'll
apply too much voltage to the filter caps and receiver.

If you're going to simulate a selenium rectifier, you'll probably need
to add a series resistor to drop the voltage somewhat.

http://hhscott.com/cc/rectifiers.htm
http://wiki.answers.com/Q/Can_you_re...o n_rectifier

Also, watch out for dead electrolytic filter capacitors. They will
need to be "reformed":
http://www.vcomp.co.uk/tech_tips/reform_caps/reform_caps.htm

Single element rectifier
Siemens lazy S logo
Made in Germany
2250c50
Kc 0.6e 11/16
--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558