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Originally Posted by Charlie
The tuning eye is a 12ZE8. I havent' found this number anywhere, and no substitutes. I'd like to get a fresh one as this one is very weak. If someone comes across a listing for this tube, please let me know.
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Charlie,
I've never heard of a 12ZE8 magic-eye tube. The ones I remember are six-volt units; 6U5 and 6E5 come to mind. (There is also the EM84, which is a tuning-eye tube but the display is two bluish-green bars that indicate proper station tuning; these were mostly used in old Grundig and other makes of all-wave receivers of 1950s vintage.)
If you can't find a 12ZE8, perhaps you could rework the filament circuit (with a separate 6.3-volt transformer, and a resistor in place of the original tube's 12-volt filament so as not to upset the voltage drop across the heater string) to allow the use of one of the 6-volt eye tubes. There should be plenty of old 6U5's/6E5's around if you do a little looking, or if you have (or can find) a junker set with a good eye tube, that will work as well.
If your set's tube is getting dim, it is almost at the end of its life and should be replaced anyhow. Another dead giveaway that the eye tube is getting weak is if you see red splotches around the target electrode inside the tube, as you look straight at it. I don't know exactly how this ties in with a weak eye tube, i. e. what happens to the tube to cause the red tinge on the target element, but I remember reading in an old issue of Radio-Electronics magazine that this is one of the telltale signs that the tube is getting weak and is likely on its last legs. I remember reading in the same magazine that had this information one technician's story about a customer who brought in an old set to be repaired; she told him, "The radio works well enough, but the Magic Eye is all bloodshot!" Sure enough, when the technician turned the radio on to test it, he noticed a red tinge on the target electrode of the 6U5 eye tube as soon as the set warmed up. A new tube cleared up the problem, and when the tech tested the eye tube later on, yup, you guessed it, the cathode emission was much lower than normal.