Convert 12.6Vac xmer to 13.5Vac

The 3cx800a7 tube filament voltage specification is 13.5Vac +/- 0.6
The conversion here involves a 12.6Vac 3A rated transformer to power two 3cx800 filaments
A 3CX800A7 tube current is 1.5A at 13.5Vac
Originally, This transformer voltage measured 12.8Vac with two 3CX800 filaments as load.
Too Low

Transformer with Case removed






This being my first time into this transformer, I looked under the tape on the LV winding side.
My comment would be NOT to cut the tape. Wind added turns over it.
there are two layers of tape cut in photo.
outer tape covers connections, the next covers the LV wiring headed down side of transformer - on this transformer.


I used #16 enameled solid copper wire for added windings. Tight fit...


Added paper insulation between outer core and added windings. LV wires leaving transformer were epoxed at tywrap.
Heatshrink applied on new solid #16 wire. Scott tape was removed before installing case back on. Added three turns. Open circuit voltage before 14.2Vac, after added windings 14.8Vac

with two 3CX800A7 tubes connected the voltage was 13.55Vac - DONE!



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xmer 3CX800

Last updated 10 May 2020