The AM Forum

Learned or re-learned a lesson today on neutralizing using the BRUENE method, which is a capacitive voltage divider on the grid tank of the final. A typical Neut cap is  a HV 15 to 25 pF variable and the bypass cap is usually 25 to 50X larger like a 680 pF and a This is a common way to neutralize 6146 tubes.
I forgot that you really need a choke or at least a resistor, from the bottom of the tank down to yout BIAS supply. Otherwise it won't null properly.

I typically use the reverse method, which is pumping a signal generator into the SO-239 usually throgh a 6 or 10 dB pad. Then you clip the 10X scope probe on the top of the driver plate (which is usualy the grids of the finals). I do this with fils lit but no HV.

Set the gen on a frequency (highest band is typical). Bring up the level so you see something on the scope. Now max everything:  the plate tuning, Loading and the driver tank. With the scope at full deflection with a few 10's of mV P-P showing, rock the neutralizing cap for your null.

By the way, I was neutrlizing my homebrew 630M rig w which uses a pair of 6146's.

I like that transmitter and the LF bands. Any chance of pics of the inside?

Oh yes, round knobs.

Yummy. ;)

73DG

I am publishing a video on the beast as part of my 630M Adventure series that I am doing on WHOTUBE Mikrowave1 Channel. It goes through the problems and victories.

But here are a few pics.