05-03-2010, 08:56 AM
Well a few things come to mind.
As for the hum try bridging a larger cap across your filter cap. Like 20 or 30 mfd @ 450v. If this helps then go with a bigger filter. Make sure that the negative side is NOT connected to ground but to the center-tap of the power transformer which goes though a resistor the ground. This provides the grid bias for the output tube.
Make sure your 2nd det tube is good and has the shield over it. Not only does it act as a detector but as a very high gain amplifier. It can pickup hum from the power transformer. Any leakage from the cathode to grid will give you hum.
Distortion can be from the wrong bias voltage on the output tube's control grid. Poor alignment, and having the regeneration control set too high.
Some food for thought
Terry
As for the hum try bridging a larger cap across your filter cap. Like 20 or 30 mfd @ 450v. If this helps then go with a bigger filter. Make sure that the negative side is NOT connected to ground but to the center-tap of the power transformer which goes though a resistor the ground. This provides the grid bias for the output tube.
Make sure your 2nd det tube is good and has the shield over it. Not only does it act as a detector but as a very high gain amplifier. It can pickup hum from the power transformer. Any leakage from the cathode to grid will give you hum.
Distortion can be from the wrong bias voltage on the output tube's control grid. Poor alignment, and having the regeneration control set too high.
Some food for thought
Terry
When my pals were reading comic books
I was down in the basement in my dad's
workshop. Perusing his Sam's Photofoacts
Vol 1-50 admiring the old set and trying to
figure out what all those squiggly meant.
Circa 1966
Now I think I've got it!
Terry
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