Check continuity of the 50Y6 filament between pin #2 and #7.
Only a few things that can cause lack of tube lighting. Bad line cord? Volume Control Switch? 400 ohm resistor open?
One filament pin goes to 400 ohm resistor. The other to switch.
Norm
:My Sears model 6951 is just dead. One filament pin on the 50Y6gt goes to the on/off switch and there is nothing to the other filament pin. What should go there? I tried a 400 ohm and then a 1K ohm from the line in but the tube still did not appear to light and no sound.
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The schematic for this set is on this site under Resources. It will tell you everything that you need to know vis a vis connectivity.
I saw the schematic but it is not very readable. Anyway I have a new tube (50Y6gt) and checked the continuity of it and the switch. I tried a 470 ohm 2w resistor and it gets hot. Seems like it probably should be a 10W resistor or more. Is that right? I don't see any resistor like that in the set. Looks like there was a wire wound at one time but is gone now except for a short piece of wire remaining attached to the socket pin.
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The 400 ohm resistor drops 60 volts @ 150 ma. 60 volts times .15 amps = 9 watts. You should use a 20 watt resistor and even it will get hot.
Here is an idea. Change the tube from 50Y6GT to 117Z6GT. This tube will operate directly off the AC line and doesn't need a resistor. No change in base wiring. Just replace resistor with a wire.
Norm
:::My Sears model 6951 is just dead. One filament pin on the 50Y6gt goes to the on/off switch and there is nothing to the other filament pin. What should go there? I tried a 400 ohm and then a 1K ohm from the line in but the tube still did not appear to light and no sound.
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::The schematic for this set is on this site under Resources. It will tell you everything that you need to know vis a vis connectivity.
:
:I saw the schematic but it is not very readable. Anyway I have a new tube (50Y6gt) and checked the continuity of it and the switch. I tried a 470 ohm 2w resistor and it gets hot. Seems like it probably should be a 10W resistor or more. Is that right? I don't see any resistor like that in the set. Looks like there was a wire wound at one time but is gone now except for a short piece of wire remaining attached to the socket pin.
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Power is IIR or (.15)(.15)(446)= 10.035 watts. So a 10 watt resistor would overheat and eventually fail. One guideline is to multiply the expected power dissipation by 1.7 (or 2, if you are very conservative) and then select the next-closest higher-power-rating resistor. So in your case, you would want a 20 watt power resistor.
Using Ohm's Law as above, you can compute the effect of using a higher-value resistor instead of the 446 ohm unit. The tube has a characteristic resistance of R=V/I or 50/.15 or 333 ohms. So putting a 470 ohm resistor in series with it would give a current of 145 mA and would subject the tube to 48.5 volts. So it should still work OK. But you will still need a 20 watt resistor.
Or how about adding another 50 volt tube in series as a ballast? Yes, you would need to add a socket, but a tube will dissipate the heat better than a resistor under the chassis, no? It could even be mounted with a clamp, like an eye tube.
He would still need a series resistor to knock down the current to the correct 150 mA level. Two 50 volt tubes in series, with no resistor, would give a current of 175 mA and a per-tube drop of 58 volts- too high.
Anyway, power resistors are cheap. I picked up a couple of 390 ohm/10W resistors at the local electronic experimenters' store (a vanishing breed)to sub for a field coil in a Midwest RC-16 for $2.09.