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Jerry,
Using the braid as the primary has a lot lower loss than just using the inner conductor as teflon wire. That Idea came to me after remembering reading an article on low loss combiners on the W6PQL? page where he does similar to create low loss splitters and combiners.



I decided to try if this broadband transformer scheme worked for the output transformer and it did. Its probably not yet optimized but so far it does what I wanted it to do optimization can come later.

John

I have just finished building a version of W6JL's linear. It has fantastic! performance. 40 watts upto 14 Mhz, 30 watts on 21 Mhz with -30 db IMDR. The changes I made were to replace the output transformer with one made by stacking FT37-43 toroids (4x2) and simplifying the biasing arrangment.?

The biggest challenge is to safely get the heat out of the transistors to outside air.

?

Jerry,
I started with the latest kit.?
The output transformer was done as follow. I had ultra small Teflon coax in my junk box so I took a piece, removed a piece of insulation from one end, tinned it and stripped it back leaving a small amount of braid to attach a bare wire to as one side of the primary. The center became one side of the secondary. Then I made 2 full turns on the binocular core, marked the cable and removed it. Removed the outer insulation of the extra cable that was not inside the core so I ended up with about? 5 inches of cable with? ~2.5 inch of insulation? removed. I then tinned the area close to the insulation and scored it with an exacto knife so that just about 1/16 inch of braid was left.and removed the rest of the braid. So, at this point the cable is as follows . one side center wire tinned and the about 1/16 braid has a piece of bare wire then a 2.5 inch long piece of cable with insulation and braid with the insulation ending showing 1/8 (or shorter) of braid and the center going on another ~2 inches (I used a random long enough piece to make the task easier and then trimmed back the center) now I wound the cable end with the insulation and braid on the torroid for full 2 turns and attach a piece of bare wire to the braid for the second primary connection. So now it looks like this: A binocular core with 2 turns of coax with 2 connections to the shields, one side center about 1 inch and the other side center about 2 inch. Now take that 2 inch center piece and put it through the core one more time for a full turn. Now you have 2 turns of the shield as primary and 3 turns of the center as the secondary. The 100pf cap went parallel to the primary winding it improves the output power. I might build a transformer with 2 cores to see if it is still needed. Why Teflon? Because I had it and? because it doesn't melt when soldering to it. Tinning the screen of Teflon coax is easy and trimming it also.

John