Voltage Regulator Tubes

[Meir WF2U]

Bob,

If you're getting out of the tube 128 volts, seems like it's not regulating.
Measure the current across the voltage dropping resistor which is  
feeding the regulator tube. The current which has to be going through  
the tube to ignite and thereby regulate is around 15 mA, so if you're  
not getting at least that much current across the dropping resistor,  
it's positively not regulating. I never saw a regulator tube of that  
family that aged to the point that it changed regulated output voltage  
by that much, provided it was fed correctly.
Anyway the current across the dropping resistor should be 15 mA + the  
current draw of the circuit supplied by the regulated voltage, which  
is probably less than 5 mA (I don't have the SX-73 book to look at as  
I'm at work...). I have a great working  SX-73 which required only a  
shorted capacitor replacement in the bias circuit.

73, Meir WF2U
Landrum, SC


Quoting Bob Krassa <bob at KRASSA.COM>:

>
> The Hallicrafters SX-73 that I am working on has an OC3 or VR105 voltage
> regulator tube.  But it regulates at about 128 volts instead of 105.  I have
> heard about this before.  My question is - did some of these tubes regulate
> at the wrong level when new, or is this caused by aging?  And is there
> anything that can be done about it, like running them briefly at a high
> input voltage?
>
> 73s Bob Krassa AC0JL
>
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