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There were sets that used both the 26 and 27. My 1928 Atwater Kent model 40 (oldest radio I own that I've made work) uses 3 26 TRF stages a 27 as a grid leak detector, and IIRC a 26 1st audio and a 71 output.
I'm using the later RMA standard numbers for those types to avoid repeatedly typing UX- on my phones tiny keyboard.
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