Reading cathode and grid current

genemckinney · Post by **genemckinney** » Tue Aug 11, 2009 8:30 am

I have a filament transformer WITH NO CENTER TAP...and I want to be able to read cathode current and grid current using separate meters in the new amp I am building.
Can I use resistors across the winding...or diodes? What about connecting to one leg of the winding? Will this work...and what is the disadvantage to this method?

Thanks
Gene
W5CBS

N9LCD · Post by **N9LCD** » Tue Aug 11, 2009 10:35 pm

Gene:

My old RCA Transmitting Tube Manual, circa 1938, shows a 50-ohm wire-wound resistor across the filament supply to create an "artificial" center-tap. They don't specify wattage but it must be pretty high.

I can scan & email some theoreitical schematics if you're interested.

JERRY

N9LCD

genemckinney · Post by **genemckinney** » Tue Aug 11, 2009 11:11 pm

Hi Jerry...

Thanks for the note. I have installed two 100 ohm WW resistors in series across the 10 vac filament winding...reading cathode and grid current at the center junction of these resistors...using separate grid and cathode meters on my linear amp. I have a floating B minus connection.
I knew you could do this, but didn't know what value to choose when it came to the resistors. I guess we can call this an "artificial center tap"...

Thanks Again...Problem solved...

Gene McKinney
W5CBS