On Jul 23, 7:35*am, "Brenda Ann" wrote:
"N_Cook" wrote in message

...

No user switchable option. I can see its possible to rewire the vibrator
so
you still get right polarity for the anode supplies. Heaters presumably
happy enough powered the other way round but how to change the biasing of
the valves ?

Unless it's a synchronous vibrator, it should run equally well on either
polarity. The radio doesn't get anode voltage from the car's DC, it gets it
from the radio's DC-DC converter (vibrator, transformer, rectifier,
filtering).

Sounds right. But as not in this posting, do recall at least one 12
volt European car radio of the 1950s that had a polarity plug that had
to be placed in the correct position. But reading this now can't think
why that was necessary! Maybe they were synchronous vibrators or
something.

BTW not pertinent to this posting but have operate an item of 6 volt
DC w. vibrator gear by feeding in 6.3 volts AC from a radio, removing
the vibrator and strapping one half of the input winding of vibrator
transf. to the supply. So instead of alternatec pulses of DC to each
half of the CT input winding, we had 6.3v 60 hertz AC constantly to
half the winding.

Don't understand the biasing question?