6JS6 vs. 6LR6 vs. 6LX6 tubes

[Chad Hauris]

I'm working on a 1968 Sylvania D12 that originally used a 6LR6 HO tube. The problem was very low boost voltage and very low HV. I put in all new electrolytics and new diodes in the power supply and the primary supply voltages are good. As a test I tried a 6JS6C from a junk Sylvania chassis and the set comes on with good width and 25 KV HV. HO cathode current is 200-210 ma. 6JS6C was listed as a subsitiute in an online tube data page.

Does this sound like it would work as a sub? The 6LR6 has a bigger plate than the 6JS6C so it seems like it maybe is rated a little higher. Also I have a brand new 6LX6 which looks very similar to the 6LR6 but even looking at tube manuals its hard to tell if it will sub and I don't want to ruin something. I'd like to replace with a tube I already have rather than having to pay big $$ for a new 6LR6 if possible.