| Here is a photo of the
12v D.C. power supply to run a Paraset from a 12v automobile battery. This
psu has proven to be 100% reliable. It runs cold and only gets just discernably
warm even after being left on for hours. The 9v-0-9v transformer must be
50VA rating. If you use the components as stated in the schematic (see the
schematics page) then this psu will give trouble free running. It has turned
out to be particularly well regulated and oscillates at just a little over
50Hz. No special precautions are needed to remove any interference since
it does not produce a lot of electrical noise in operation. It is a wise
precaution to at least build it in a metal box since this should provide
all the screening needed.
Geoff likes to run the heaters from the
12v battery using a resistor as a voltage dropper to remove the excess 6v.
This is wasteful in power terms but if you use a big enough dropping resistor
(with a heat sink) is 100% reliable. If your Paraset uses two off 6SK7 and
one off 6V6 the total current drain for the heaters will be 1.05A. Assuming
your battery is a 12v battery (probably near to 13v in practice) then you
need to drop approx 6.3v or so. This means a 6 or 7 ohm resistor will be
needed.
The 6SJ7 will work in place of the 6SK7.
The heater current is the same...0.3A at 6.3v. The 6V6 draws 0.45A at 6.3v.
12SK7 and 12SJ7 are also interchangeable, but the heater current in this
instance is 0.15A at 12.6v. 12A6 has a 12.6v heater and draws 0.15A. So if
you want to use 6v (actually 6.3v) heaters use 6SK7/6SJ7 and 6V6 valves.
If you want to use 12v(actually 12.6v) heaters use 12SK7/12SJ7 and 12A6 valve
line up.
Remember if you use the 6v heater valves
from a 12v supply you will need a dropping resistor or appropriate
regulator. |
