Upgrading the PA output transformer

JerryW0PWE notes that in the posts on boosting and/or leveling output power he saw pictures of a binocular core being used as the output transformer in place of the toroid that comes with the uBitx board.  He asks “What size is that binocular core?”

Allison plans to use the longer version of the BN43-6802 (or two BN43-302 cores end to end).

John VK2ETA says he went back to IRF510s in the finals and has used a BN43-3312 as the single 302 was getting warm on the low frequencies and he could not put more than 2/3 turns in the core.  He tried both 1/2T and 2/4T in the 3312 and settled on 2/4T due to better efficiency. The 1/2T drew too much current at 80M.

There is plenty of gain and power at 14MHz and below on 16.8V for the PA but has had to resort to a gain control for flattening the power curve despite 330pF caps in all 6 drivers emitter resistors, 22uH inductor in the base feedback of  the pre-driver,  330 pF across the primary of the finals transformer and 820ohms in the finals feedback resistors.

Nick VK4PLN uses the BN43-202 with a winding ratio of 2:4 using 0.64mm enameled CU.  His rig is outputing 20W+ on 80/40/20 using RD16HHF1.  Nick doesn’t detect any heating… Maybe it will at that power level on 10m?

His plan is to now try using:

– the MPSH10 in the pre-driver
– a single 10T bifilar wound FT50-43 for feeding the power to the RD16HHF1s
– removing the PA feedback loop
– and other pre-driver mods as per Farhans suggestions….

This appears to be the common approach on most of the RD16 amp designs out there…and Nick hopes he will get 20w+ output from 80-10m….

Bill K9HZ tried a BN61-002 and it seems to be a winner.  It doesn’t heat up at full power and it seems to be extremely wide band.

Reference

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