[R-390] Ballist Tubes

[David C. Hallam]

I recently acquired a Boonton 250A RX meter.  While it seems to be working
properly, I have found a problem with the 6.3 V heater line.  Boonton used a
6H-6 ballast tube to regulate the heaters in the bridge oscillator tubes and
the mixer tube.  The spec calls for 6.3 +/- 0.3 volts.  I am measuring 8.3 V
with two different AC voltmeters.  AC line spec is 105-125 V so I am OK
there.

Can ballast tube fail in such a manner that it will still pass current but
fail to regulate?

David C. Hallam
KC2JD