[MrFixr55]

@Morzh, Roger and anyone else interested- A 6A8? I am trying to figure out how a 6K7 (remote cutoff pentode) would work when a triode-heptode is called for. Pin 6 of the 6J8 is the oscillator plate. Pin 5 is the oscillator grid, also connected to grid 3 of the heptode (the oscillator signal output to the mixer?). On a 6A8, Pin 5 is G1 (the oscillator grid), pin 6 is G2 (the oscillator "Plate Grid). The 6A8 is not the correct tube to drop in for a 6J8, but at least it may oscillate, tune and mix, based on the connections to it (The RF input to the mixer is the grid cap in both tubes).

I have NO idea how a 6J7 or 6K7 pentode would work, as pin 6 of the radio (the 6J8 Triode Plate) has NO connection in a 6J7 or 6K7. Since that oscillator plate circuit contains the primary of the oscillator coil, having no connection means having no oscillator.

For all following this very interesting but wordy (my fault) thread, attached below is a link to the 1940 edition (RC-14) of the RCA Receiving Tube Manual, courtesy of the World Radio History website:

https://www.worldradiohistory.com/BOOKSH...14-OCR.pdf

The worldradiohistory.com website has many, many useful documents, from all revisions of the RCA Receiving Tube Manual to several of the RCA Victor "Red Books" plus so much on the history of radio. I urge all members to have copies of the RCA Receiving Tube manual, as it is very useful in getting the pinouts that may not be listed on schematics, to some rather good theory on the different types of tubes (diode vs triode vs tetrode vs pentode, etc.) I often cite the 1940 version (RC-14) of the RCA Receiving Tube Manual because it has the best descriptions of the tubes used in pre-war Philcos.

Since so many of these tube numbers sound so much like each other care (at least more care than i used at times) must be used in confirming the tube number. For example a 6J7 and 6K8 are VERY different tubes.