[R-390] 3TF7 Ballast Tubes

[Roy Morgan]

Ballast Tube Folks,

<Dead Horse Beat Mode ON>

I recently unearthed a Boonton Model 250A RX-meter and poked around  
inside with a voltmeter.  It uses a 6H-6 ballast tube to feed the  
filaments of two subminiature oscillator tubes.  The filament voltage  
should be 6.3 +/- 0.3 volts.  It was 7.7 volts.

The ballast tube was operating, but one of the four segments of the  
filament was glowing quite strongly, with the other three segments  
dark.  Not having a spare 6H-6 handy, I tried a 6V6, 6H6, and settled  
on a 6AG7, which gave 6.6 volts for the filament.

The (next to) bottom line is:  even if the ballast tube is operating,  
it might not be working right. Measure the filament voltage(s) on the  
supplied tube(s).

<Dead Horse Beat Mode OFF>


Roy

Roy Morgan
k1lky at earthlink.net
K1LKY Since 1958 - Keep 'em Glowing!