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.

most 12 pin compactron sweep tubes are similar enough to sub.its a waste to use that 6js6 in a tv when it will fit my yaesu 101 ;-)
i remember seeing js6 and lr6 used intercangeably in those sets.the lf/lx has slightly higher plate dissapation.

That set uses.a 330 volt b+ and a higher cathode current tthan the zeniths correct? The lr is a more robust tube for sure but the js should work fine, maybe not last as long. Your cathode current is low if that's the cahssis I'm thinking of. Lower b+ higher cathode current same wattage. Beware of the orange drops in that set. They will drive you nuts mainly with vertical roll.

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I have the sams if you need it. 330 volt b+ and the sams says 210ma but someone noted 270, if your getting 210ma thats excellent

I would expect 210ma with 410 volt b+.

Thanks for your comments, I do have the sams...I have a feeling something else is not right as the vertical still doesn't fill the screen even with a new vertical output tube and height all the way up. It may be those bad orange drops! When I turn the effeciency coil I don't get very much variation in the HO current,just goes between 0.20 and 0.21 amps with the 6JS6c.

I have had several cases of HO tube destruction caused by no drive signal...hopefully the old 6LR6 didn't suffer this fate. It never seemed to look abnormally hot though.

I have a feeling I maybe just better do a re-cap of all those old orange drops like you said. On anything that has paper caps I automatically replace all of them just so I'm not chasing weird problems.

I brought home a few of those form SC and they all had exactly the same failed caps in the vert circuit. Those sets have the easiest to remove chassis, the traces on the boards are crappy though. They lift right off
That set can produce a superb picture, I would rate them close to the RCAs of that area.
I have a brand new 0 hour 25" D12 out in the garage I havent even tried yet. I would bet the same caps are bad in it too.

Glad to know this info...I have a D12 remote set in storage I plan on using in the future. Also have a D08 that probably isn't all that different.

Tonight I went ahead and tried the 6LX6 and the width was even better and the boost voltage came up to the full 900 volts. With the 6JS6C boost voltage was about 100 volts low and the width almost filled the screen but not quite. I had an offer to help me out with a new 6LR6 tube so that ought to work really well.
Next I am going to replace all those old orange drops in the horz and vert sections. The set I got the 6JS6 from had a bad flyback but I think it was a D09. The D09 had a lot more tube based functions. The D12 only has tubes in the vert/horiz outputs and oscillators, video output, chroma output, chroma oscillator, damper, Hv rectifier and regulator.

the traces on the boards are crappy though. They lift right off


My experience, too, with Sylvania sets that age. Amazing how easy they can lift.

Are the Russians making the 6JS6 yet? Seems like a good candidate.