Problems with Zenith K731

[gdunlapsd]

Originally Posted by DaveWM

AM and FM uses the same IF tubes but for the last, the FM limiter, but I doubt that's it. Might be an alignment issue, esp on the last stage of the discriminator, but with out proper tools and know how you should not attempt to adjust. Unless a resistor is WAY out I can't see how this could be it, like 500% or more. Most tube designs work fine with out of spec resistors, unless the resistor is in a tuned circuit or is gold banded.

One of the resistors to the limiter (R25 on the 7k07 schematic) is off a bit, supposed to be 4.7M, reads 5.7M; I'll change it out tonight. There's also a large, 3watt 950 Ohm resistor that reads 980 Ohms, maybe changing that out will help, though it feeds A and B which both read fine.

There is a resistor inside the FM section (R5) that's supposed to be 680 Ohms but reads 717 Ohm; maybe that's the culprit? I don't relish the idea of taking off the metal box that's enclosing it but I may have to.

I agree about alignment - don't want to go anywhere near that.