Some Zeniths manufactured in 1937, and possibly others, have problems ranging from lack of sensitivity and tuning eye response, to very poor performance. In extreme cases, the set will not work at all. Voltages to all points in the set appear normal and resistance measurements everywhere look good, including the windings of the I.F. coils. This is a problem that began showing up back when the sets were only a few years old, but for some reason, many of us today are not aware of it.

For a short period of time, maybe for one production run, the I.F. coils were wound on a hard paper tube instead of a dowel. It may be possible to identify these coils without going into the cans. A resistance measurement of the windings is all that is necessary in most cases, if you have an accurate meter. The windings should measure 6 or 7 ohms. Even a few ohms difference can affect the performance. Some of these windings will measure up to 90 ohms without affecting the grid and plate voltages any to speak of, and can lead you to believe they are OK. Some of these resistances have been found to be as high as 3000 ohms, but these extreme cases should show up in early testing.

In order to assist some of you with only a small about of Zenith experience, the cans, or shields, of the I.F. transformers can usually be removed from the chassis, leaving the transformers themselves still in the circuit. This will allow you to inspect the coils to determine the type used. If they are wound on a hollow form, you have a potential problem. This is not to say that all of this type are bad. Some still work well, and after all these years, if they are still good, they have stood the test of time, and will probably remain that way. If they are suspect, the only real cure is to replace them with the solid core type.

It is possible that you have a receiver giving very good performance, and believe it can get no better. The set aligns properly with good peaks showing as they should, and everything appears normal. Well, maybe the tuning eye isn't quite up to par, but what the heck? That's normal. But if you find an I.F. transformer that does not measure quite as it should and replace it, chances are good that it will come on like gang busters in a way you would have not thought possible. You may even have to go back into the circuit and change a few little things you did to get the tuning eye to respond better. It may be working too good now.

One other little tip is in order here. When measuring resistances in the range required for making this test, some of the meters we use are not really up to doing so without paying special attention to the resistance of the test leads. You may be in good shape if your meter reads zero ohms when the test leads are shorted with each other, and you may not be. You can make allowances for this if it reads off some, but some of the cheaper digital meters are not that accurate in this range regardless of what you see. It has been found, using precision resistances as a standard, that some of these meters are not all that good when measuring only a few ohms. It has also been found that a good vacuum tube volt meter is hard to beat in some of these instances. LONG LIVE THE VACUUM TUBE!!

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