The AM Forum

Just when I had it working just fine, I had to go "fix" it.

I built another power supply so the mod and RF could have their own.  One is 1000v and the other is 900v so I took Don's suggestion and put the higher voltage one on the mod.  Those number are under full load.

I changed nothing else other than removing the link between CT and RF b+ on the mod trans and now the best I can get is about 35% modulation.

Is there something else I need to know about using separate supplies?  I have never had the option to do it this way.

Another thing that bothers me is that the RF plate current still dives down on modulation.  In fact, it seems worse than before using one supply.

Any thoughts?

js

The mod transformer must be miswired, or the 1000V supply output capacitor is open.

Downward mod on the RF stage... maybe try more grid drive and see if it helps.  If it does, I think the drive circuit needs some twiddling.