Here's a new one I never encountered before. Working on the Zenith model 8S463 I picked up last weekend. It's been recapped / (most) new resistors, all carefully installed. Checked and double checked. The radio plays, albeit a bit garbled. However when I plug in known good, bright green 6U5 / 6G5 eye tubes, they don't light up green at all! I can see the filament lit bright orange, and the voltages are there on the eye tube socket plug, but no green. It's like a dead eye tube. I take it out, test it in the tube tester, and it shows bright green. Any ideas what would cause this? I have a new 1 meg resistor across pins two and 4.
Here's a link to the schematic:
http://www.nostalgiaair.org/pagesbymodel...025455.pdf
I'd double check all the voltages while the tube is plugged in. If you don't have a tube manual the 6U5 is p. 141 in the following manual:
http://www.tubebooks.org/tubedata/RC15.pdf
It sounds like your plate voltage might be missing or low. That 1 meg resistor (if open) will keep the eye from closing.
Have a look at R-18 to be sure all of it's sections are ok. The 52 ohm section is the ground return for the I tube among other things.
On Zeniths the 1M resistor that is usually located inside the socket often is open.
One way of replacing it without opening the socket (which is backelite and appears to already have cracks so opening it almost guarantees it won't survive it) is the way I did it for my Zenith 9S262.
You could find the topic, from, I think, year 2012.
In essence, I took a surface mount 0603 resistor, which is small and flat, soldered two thin strands of wire to each end, threaded them in the appropriate pins, laying resistor flat on the surface and re-insert the tube. The power dissipation is negligible so this works just fine.
Found it, here it is.
http://philcoradio.com/phorum/showthread...th+9-s-262
The photos are on the last page of the thread.
All is well...once I got my head on straight I realized I counted the pins counter clockwise instead of clockwise. It's shining green once again
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Yeah that stuff will get you dizzy
I restored an 8s463 about 8 years ago. Very nice sounding radio! Glad you got the eyeball working, as I had to replace the meg ohm in the socket on mine. Tedious, but do-able!
Most definetly check the resistor at the tube socked base. takes a little work to get to it but take he cover off of the socket to the tube , read the resistance with tube removed from socket.
Oldswab,
He said the tube is working now