[Boatanchors] 0A2 regulation

[JAMES HANLON]

Steve,

First off, you are correct about the max current rating for an 0A2 being 30 ma.  The VR tube should be connected through a series limiting resistor to a voltage source.  In the case of an 0A2 whose regulating voltage is 150, the power supply voltage source should be 185 or more.  Per my 1952 ARRL Handbook, "The value of the limiting resistor must lie between that which just permits minimum tube current to flow (5 ma for an 0A2) and that which passes the maximum permissible tube current when there is no load current.  The later value is generally used.  It is given by the equation:  R = [1000 (Es - Ex) / I ] where R is the limiting resistance in ohms, Es is the voltage of the source across which the tube and the resistor are connected, Ex is the rated voltage drop across the regulator tube (150), I is the maximum tube current in milliamperes (30).

Two regulator tubes can be connected in series to give a higher regulated voltage.  In the above equation, Ex would just be the sum of the rated voltage for both tubes.

Connecting two tubes in parallel can be a little more tricky, because one of them is likely to have a little lower regulation voltage than the other and that one will hog most of the current.  Back in the day when I did have two VR-150s in parallel, I had a small equalizing resistor connected in series with each tube before they connected to the limiting resistor to help equalize the current flow in each tube.  That will spoil the voltage regulation a little bit, but it will allow a higher current to be regulated.  I'd recommend you measure the current through each tube and adjust the equalizing resistors as needed to obtain an acceptable current balance between them.

Jim, W8KGI