There are a wide variety of opinions about speaker field coil power supplies.
Some believe any lab supply will do - switching or linear. Others insists only Selenium rectification is best while others insist that Tungar is the only way for the best of true field coil sound. The focus is on rectification in these last two cases. It is entirely possible that batteries were originally used and so the 7 volt specification of the WECO 555's, Tungar battery chargers were used to recharge them and then only later employed directly.
A supply's performance relies on much more than the rectification type. If a supply is well designed rectification influence is lessened.
After listening to many types it seems that choke loading makes the most noticable improvement and Schottky diodes work very well in this application. The sound is only slightly different from Tungar being a little less "you are there" and a little more "they are here".
I prefer listening more in person rather than going to an event in my mind.
Then there is the connector, something which is rated for the amperage and easy and sure to connect. Avoiding the any possibility of cooking a voice coil while connecting in the dark or under other handicaps which can occur during listening sessions.
These snap in with a noticeable click so that they communicate when they are connected. Turn it on and that is that. The they are set for each speaker type in its application and we provide these with our field coil equipped speakers to ensure the correct type supply and to avoid having to worry about such things.
Outside right now there is another story...
It has begun to end once again... the the lovely, and grave, deciduous cycle...