Reusing Electrophoresis Power Supply Transformer

[EntropyWizard]

I acquired an old tube rectified electrophoresis power supply at an auction for peanuts, and am hoping to make use of some of the parts for a low voltage linear supply. The transformer is interesting, it has both a high voltage secondary and two high current low voltage windings, presumably for filament heaters.

For this supply the low voltage windings were simply cut and a separate filament transformer was used. I traced the circuit diagram as linked below.

The transformer has a lead that was clamped under the transformer case shorted to the core. This is similar to MOT transformers where one end of the HV secondary is grounded to the core. However, I could not find continuity with any other lead, and the lead appears to exit the winding on it own.

I though to insulate the high voltage leads (open) and use the low voltage windings to build a power supply. Does this seem like a reasonable use for this transformer? What is the purpose of the lead grounded to core (which would then be attached to earth/chassis ground ?) Would a transformer of this age and type have safely intact windings/insulation? Thank you for any information.

[bob91343]

That extra wire is probably connected to an interwinding shield.

However, be aware that the output power of a transformer is intended to be divided among its secondary windings.  If you don't use all the secondary windings you might think that allows you to draw more power from the remaining windings.  In theory yes, but the wire size limits the safe current.  So you can't just take the unused power rating and add it to the windings you are going to use.

[EntropyWizard]

Thanks, that was helpful, I was able to search more info about interwinding shields. It does look like that wire is soldered to something (the shield) in the winding layers. I'm guessing this was a re-purposed transformer for audio devices, since electrophoresis supplies would be low volume production and probably didn't need extra noise reduction.

I'm attaching a picture of the transformer label. The total VA supported is not shown, but I assume it supports the currents listed for the secondaries simultaneously. I thought I would use commonly available 3A regulator devices, and seldom really hit the kind of load.

I'll have to do some testing to make sure it can support the needed voltages under load.

[bob91343]

That Stancor transformer was a popular commodity back in the 1950s or so.  They are considered useful today as replacements or for new designs.  With 200 mA capacity it can handle even large loads, perhaps 80 Watts not counting the filament windings.

With a 5U4 rectifier it can produce voltage useful for small transmitters or big receivers or for a variable regulated power supply (with some accessory power tubes as pass elements).

For what end use do you consider it?  It could be useful as a source for repairing vintage tube equipment.  I own a commercial version of that, that I have never used.  It has meters and two high voltage outputs and a variac, etc.