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#5
01-15-2012, 07:39 AM
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The 25Z5 and 43 are 25 volt tubes, and the 6 volt ones and probably the missing one all add up to 68 heater volts. The tube in your picture must be a ballast tube, which is a wire wound resistor in a glass envelope, used to drop line voltage to 68 volts. Look carefully and see if it looks like that's what it is. Try measuring resistance across all the tube pins and see what you get. Ballast tubes get very very hot in operation.
Is there any writing on the tube base? Try putting the tube in the freezer for a few minutes and then take it out and breathe on it and look around on the glass for a number. Edit: I can't think of another 4 pin tube that would make sense here. The radio could function with the rectifier, output, and the two 6 volt tubes you have. Perhaps the two four-pin sockets are for TWO ballast tubes. Some manufacturers in the thirties inflated their tube count to make folks think they were getting more radio for the money, where in fact the extra tube or tubes were not needed. Inspecting the way that the sockets are wired would tell you. If the two four pin sockets are wired in series some way it could indicate that they are both for ballast tube impressivity. If that's so there are ways around having to use ballast tubes, which can be hard to find. Time to flip the chassis over and start drawing the actual back into the schematic diagram. I've had to do that on several orphan sets and it's good practice in tracing circuits and in patience! As you go you'll see how the circuits come together. Then you can compare your set with the schematics of sets using similar tubes. There's a lookup table for that at grillecloth.com
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Reece Perfection is hard to reach with a screwdriver. Last edited by Reece; 01-15-2012 at 08:43 AM. 
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#6
01-15-2012, 12:22 PM
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Yes that is called a ballast tube, often made by Amperite. Some of them have taps for pilot lamps.
Calculate the resistance and power rating from subtracting the sum of all the heater voltages from the power line and dividing by 0.3 Amperes. If you need 68 Volts from 120 V, then you divide 52V by 0.3A and get about 170 Ohms. It will dissipate about 16W so use a 30 W resistor or thereabouts and mount it clear of components that its heat will damage. Having said that, you may still be able to find ballast tubes, assuming yours is bad. Measure across various pins to see if you can measure somewhere around 150-170 Ohms. If so, it's probably good.
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#11
01-17-2012, 07:38 PM
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So what is the other 4-pin socket for? Can you tell by the wiring? If this tube is only half the resistance needed, then you'd need two identical depending on the socket wiring.
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Reece Perfection is hard to reach with a screwdriver.
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#14
01-18-2012, 11:43 AM
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The missing tube has a four-pin socket so is not a 37 or 76. Rickey: what you are going to have to do is trace the wiring around those two four-pin sockets and report it here before we settle on ballast tube(s). My GUESS is this:
1. Power line in goes to first 4-pin. May or may not go to switch first. 2. Wire comes from first 4-pin and goes to second 4-pin. 3. Wire comes from second 4-pin and goes to first heater of the remaining tubes. 4. All the remaining tubes have their heaters connected in series.
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Reece Perfection is hard to reach with a screwdriver.
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#15
05-05-2012, 05:43 AM
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i have 3 new in box they used for regulating voltage i think somewhere in my tube schematic books i have the info on them
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