Quote:
Originally posted by dsk
Update on my first old radio. It arrived today and it works just fine. I little cleaning (which we all like to do anyway, right?) and it's sittin pretty. Now I kinda wish the dial lit up.
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I have a Zenith K731 (1963) and an H511 (1951). Neither of these sets have dial lights, although the H511 has a pilot light behind the Z crest on the cabinet. Dial lights are nice, but not absolutely necessary for proper operation of the radio; however, a lot of sets (particularly AC/DC series-string receivers) use them as inrush current limiters, as my H511 Zenith does. The radio will play OK with the bulb burned out, but it puts a strain on the tube filaments as the bulb takes up part of the line voltage (usually 6.3 volts). If it burns out, the extra voltage it ordinarily takes up in the filament string is placed on one or more tube filaments; of course, this will eventually cause at least one of the filaments to burn out. The inrush limiter function of the bulb may be observed when you turn on an AC/DC radio and the pilot light comes on very dimly at first, then brightens as the tubes warm up. When the tubes are all warmed up and operating, the pilot light will be shining at normal brightness.
Note, however, that a deformed or shorted filter capacitor or rectifier tube can and often does cause the pilot light (if used) to burn out immediately after the radio is switched on. Replace the bulb, but be sure the capacitor(s) are properly formed before switching on the power again.
An awful lot of people just leave the pilot lights alone in transformer-powered radios and TVs when the bulbs burn out. I have seen and even owned old TVs which are supposed to have pilot lights behind the channel selectors, but the bulbs had long since burned out, so the sets' owners just let it be as long as the radio or TV still played. Many sets also used pilot lights behind colored jewel lenses for on/off indicators, function indicators (Zenith and others were famous for this in their early console radios and, later, AM/FM stereo console units--the illuminated Z crest is a hallmark of the Zenith H511 series of AC/DC radios) and so on. These bulbs can be safely ignored if they go bad in a transformer-powered set, as they are just for decoration or as on/off or function indicators, but again, if they burn out in a series-string receiver, replace them ASAP, for reasons I outlined in the preceding paragraph. You will save a lot of tubes this way; as expensive and rare as vacuum tubes are becoming these days, that's very important (to be sure the tubes in our old radios, TVs, etc. last as long as possible). Toward this end, Zenith incorporated a device it called a "tube saver" in many of its table-model AC/DC radios of 1950s vintage. This was simply a surge protector which limited the inrush current at initial switch on. The surge protector was designed with a special thermal switch which cut it out of the circuit once the tubes were warm and conducting. A specially designed surge protector was marketed in the '50s and '60s for TV receivers, which worked on the same principle as the ones in AC/DC radios. The only difference I could see in the surge protectors for TVs was the current rating (many if not most large-screen televisions of '50s-'60s vintage were rated as high as 300 or even 400 watts; some early color sets, especially three-way theatre consoles, drew even more current from the line).