Hi,
indeed briefly applying a 9 V battery will open the switch (NOT a 9 V power
supply - the heater only needs about 60-70 mA which is what a 9 V battery is
capable of supplying but not much more than that). No need to keep the battery
connected, the main switch is kept open by the heat it creates on its own.
Still it would be preferable to keep the z0 (at least) and z2 (if possible)
cryoshim switches open for the entire duration because a quench may occur
after a few minutes because these cryoshim coils can get overcharged by
"transformer effect" of the main coil discharging which charges the z0/z2
coils, eventually overcharging them, leading to their quench which may freak
out the main coil… So in the end a regulating power supply with some
20 V/70 mA (all heaters in series) or 3*70=210 mA (heaters in parallel)
would be better. You may find matching 10-pin plugs in your red magnet toolbox,
as well as a set of high-power clamps fitting the charging rod helping you
to construct a cable between charging rod and crossed diodes. For a cable
you can use automotive battery cables (like used in car hifi) or for welding
purposes. 30-35 mm2 would be nice but 25 mm2 should also do (may get a bit
warm, but not really badly so - the magnet should have a current of around
110 A - at the beginning only of course).
At the same time, an unshielded 51mm magnet is rather unlikely going to see
the light of day again, so you can just go ahead and (very briefly is enough)
break the vacuum and quench it… Remember to switch off smoke detectors
and open windows & doors!
Have fun with the project,
Bert
> Am 21.05.2026 um 04:26 schrieb Anklin, Clemens via groups.io:
>
> HI Justin
>
> you can also open the switch with a 9V battery.
>
> Clemens
>
> On 5/20/2026 5:30 PM, Jeff Walton via groups.io wrote:
>> Hi Justin,
>>
>> It really is just two large crossed diodes. Large in that they can handle
>> the current that the magnet will put through it and crossed because you
>> either don’t know the direction of the current or you might make
>> a a mistake as to the direction. Also the diodes are usually mounted on
>> a large aluminum heat sink with fins to dissipate the heat. For a 600 you
>> might want a fan….
>>
>> Good Luck!
>>
>> Jeff
>>
>>
>>> On May 20, 2026, at 10:48 AM, Justin Pontius via groups.io wrote:
>>>
>>> Hi,
>>>
>>> We're planning on decommissioning our Varian 600 DDR system. It has an
>>> unshielded Oxford round bottom magnet and I have the charging rods. We
>>> were planning on pulling the vacuum and just letting it quench, however
>>> it would be nice to bring it down gently if possible.
>>>
>>> Back when I worked for JEOL some 15-16 years ago we had a diode box and
>>> small power supply to open the main switch. Before I do anything stupid,
>>> does anybody have details or schematics for such a diode box? I seem to
>>> remember it was just 2 very large opposing diodes and maybe a fan. large
>>> resistor? Any insights?
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