I have just gotten a Airline 62-345 unit operable again and would like info concerning the ME tube. I can see it lit very dimly and it actually gets a little brighter when tuned to a strong station. How bright should this be in a well lit room? Is there any way to test on a Dyna jet tube tester? What about components around the tubes?
Russ

A good eye tube should be very bright. It should be as bright as your television screen...perhaps slightly dimmer. It will be hard to select an eye tube for this radio as it only has 130 volts available to the plates. You must select the best of the best new tubes. Emission testing does not determine brightness, though poor emissions will cause poor illumination. The emission test of the tube can be fine even though the phosphor has worn out. The phosphor often wears out before the emissions of the cathode go down. Therefore an emissions test does not hold much validity with eye tubes. I do not know what voltage your tube tester uses for testing eye tubes, but usually it is low, so it will give you a fair idea of how the tube will light in a set that uses a relatively low B voltage. Usually, too, if the tube lights well in a tube tester that uses less than 200 volts for tests, it will work well in just about any radio. If the tube in your radio is glowing dimly, purchase a new one. It must be very bright. I had much trouble selecting an eye tube for my 62-306, as it uses only 150 volts B current. Amazingly a slightly used General Electric tube (red lettering) was far brighter than any other eye tube I own, new or used. It is the only one that would work properly in the set. The others were all weak in the set even though they performed just fine in sets that have 290 volts available.

I guess a test that would tell if the eye tube was working properly or not would be to test it in a dark room with your eyes adjusted to the dark. If it slightly hurts your eyes at first or at least you can feel a slight strain even if there is no pain, then it's good. This all depends on how sensitive your eyes are, of course. You should be able to see it very well in a normally lighted room, and with your hand about a half foot away (perhaps a full foot), you should see a good green reflection on your hand even when near (not right next to) a 100 watt lamp.

Thomas

:A good eye tube should be very bright. It should be as bright as your television screen...perhaps slightly dimmer. It will be hard to select an eye tube for this radio as it only has 130 volts available to the plates. You must select the best of the best new tubes. Emission testing does not determine brightness, though poor emissions will cause poor illumination. The emission test of the tube can be fine even though the phosphor has worn out. The phosphor often wears out before the emissions of the cathode go down. Therefore an emissions test does not hold much validity with eye tubes. I do not know what voltage your tube tester uses for testing eye tubes, but usually it is low, so it will give you a fair idea of how the tube will light in a set that uses a relatively low B voltage. Usually, too, if the tube lights well in a tube tester that uses less than 200 volts for tests, it will work well in just about any radio. If the tube in your radio is glowing dimly, purchase a new one. It must be very bright. I had much trouble selecting an eye tube for my 62-306, as it uses only 150 volts B current. Amazingly a slightly used General Electric tube (red lettering) was far brighter than any other eye tube I own, new or used. It is the only one that would work properly in the set. The others were all weak in the set even though they performed just fine in sets that have 290 volts available.
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:I guess a test that would tell if the eye tube was working properly or not would be to test it in a dark room with your eyes adjusted to the dark. If it slightly hurts your eyes at first or at least you can feel a slight strain even if there is no pain, then it's good. This all depends on how sensitive your eyes are, of course. You should be able to see it very well in a normally lighted room, and with your hand about a half foot away (perhaps a full foot), you should see a good green reflection on your hand even when near (not right next to) a 100 watt lamp.
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From reading it sounds like it would help to have a higher B+ voltage. This radio is the 6.3VDC farm version. I'm running it with a 6vdc battery and only get 110 vdc B+. I measured B+ of 105vdc when the battery dropped to 5.9vdc. The schematic shows a B+ of 135 at 6.3vdc. So this is probably in the ballpark. I noticed that the voltage across the ballast cap on the vibrator was at 220vdc. Can this be tapped for the B+ going to the ME tube supply? If so do I have to change any other components surrounding the ME tube?
Russ

You may tap the eye tube right after L1, which will give you more flexibility in eye tube selection. Ideally you shouldn't go over 200 volts on the target for prolonged eye performance, though many radios do this. I am not familiar with the 6N5's characteristics--whether it is able to run at 200 volts or is designed for lower voltages. Other tubes that use the same wiring that are designed are the 6E5, 6U5, and 6G5, as well as others. Check a tube manual to be sure about your tube. The only risk is premature phosphor failure. Other than that, 200 volts is fine. Place a resistor of small value in series with the eye tube target lead and L1 to obtain exactly 200 volts at the target. You can connect it directly to L1 if you wish.

You can obtain wonderful results with 110 volts at the target with a new eye tube if properly selected, but changing the wiring as you stated above is probably a better idea for more flexibility. Be sure that your electrolytics are fresh for optimum B current. As for running your radio on a battery, if you live in the U.S.A., 6 volt battery chargers are fairly easy to obtain (you may already own one). They are usually sold as combination 6/12 volt chargers. A charger of 6 ampere capacity or greater is ideal, though no more than 10 amperes. You may try operating the radio from the battery with the charger connected. The battery will act like a stabilizer, but the charger will keep the system at full operation. The only problem with this is that your radio uses a low voltage 1.5 volt filamentary tube in the output section. The battery charger will likely boost the available voltage to the radio up to 6.5 or 6.8 volts with the battery connected. It can go even higher without the battery, though doubtful with the load of the vibrator supply. As long as the battery is put in place as a stabilizer, the voltage is not likely to go above 6.8 volts. This higher voltage is not a problem to either the indirectly heated 6 volt tubes or the vibrator supply. You must be sure that the voltage across the output tube's filament does not exceed 1.7 volts, though, or it will burn out prematurely. Ideally it should be at 1.5 volts. A small resistor may cure this. The other problem that may be had is hum with a filamentary tube, as the charger is not filtered. The battery will likely filter out this hum, though.

Also, I do not know where you purchase your 6 volt batteries from or what type you use, but if you have a Batteries Plus in your area, they sell 600 cold cranking ampere auto batteries for only about $45. I use one in my car all the time (1951 Chevrolet). It usually lasts 4 years with regular use, if not longer, and is capable of starting the car even when the temperature drops to 10 below zero. Such a fine but inexpensive battery will likely provide service to your radio for much longer if maintained properly. Just be careful with the acid problem and with the hydrogen off gassing while charging (explosive).

Thomas