Radio dial moves, but AM station does not change

[DirtFarmer]

Hello, newbie here. I am enjoying my "new" 1961 Magnavox FM-47 "Grand Classic" radio, and it has been working great. But now suddenly I cannot change the AM stations. The dial marker moves left and right just fine, but it stays on the same station no matter how far I move the dial. FM works just fine.

Can someone tell me what may be causing this? Is it an easy fix for a newbie? Honestly, the only thing I am capable of doing inside of this thing is change tubes. Would it be as simple as a bad tube?

Thanks in advance.

[init4fun]

Originally Posted by DirtFarmer

Hello, newbie here. I am enjoying my "new" 1961 Magnavox FM-47 "Grand Classic" radio, and it has been working great. But now suddenly I cannot change the AM stations. The dial marker moves left and right just fine, but it stays on the same station no matter how far I move the dial. FM works just fine.

Can someone tell me what may be causing this? Is it an easy fix for a newbie? Honestly, the only thing I am capable of doing inside of this thing is change tubes. Would it be as simple as a bad tube?

Thanks in advance.

Hi DirtFarmer,

Many tube radios, especially AM/FM ones with two separate tuners, have multiple tuning strings (sometimes called "dial cord"), and it sounds as if the string specifically devoted to your AM tuner has broken. Replacement string can be bought at a few places (antique radio restoration parts stores, EBay, etc), and SAMS service literature usually has the diagram for string routing

[old_coot88]

Did you try subbing the 12BE6? That's the AM mixer/oscillator tube. If it's bad, you'd still have FM (the 17C9 is the dedicated FM tube).

[init4fun]

Originally Posted by old_coot88

Did you try subbing the 12BE6? That's the AM mixer/oscillator tube. If it's bad, you'd still have FM (the 17C9 is the dedicated FM tube).

Hi old_coot88,

When I first read the OP's post I thought the same thing, but when he said it "stays on the same station" I took that to mean is is playing the one AM station it's "stuck" on, instead of the AM being totally dead as it would be with a bad 12BE6. Hopefully the OP will come along and clarify whether it is totally dead on AM or not

[old_coot88]

One station coming in across the whole AM band indicates the local oscillator (in the 12BE6) isn't running. It could also happen from a bad osc. coil (like an open winding).

[init4fun]

Originally Posted by old_coot88

One station coming in across the whole AM band indicates the local oscillator (in the 12BE6) isn't running. It could also happen from a bad osc. coil (like an open winding).

A very good point indeed, I was thinking more of the tube being dead instead of just the OSC not running. Well, the op now has a few good things to check, if he's still following the thread

[Electronic M]

I've never seen a set with a dead osc tube receive anything....I suppose it's possible if you live within a mile of a high power transmitter that a powerful enough harmonic close enough to the IF frequency could make it through the front end.

[old_coot88]

I've actually seen it a couple of times back in the day, with two stations coming in on top of each other across the whole dial. Attributed it to their heterodyne being close to the set's IF. And the osc. was dead. This was in Phoenix where there was several local stations.

[zeno]

But for now easy first. Look inside & see whats happening !
It sounds mechanical. If the dial cord is bad you can restring it BUT
it takes a certain knack which I dont have ! Most shops had one tech
with the knack that got stuck doing them all. If you order it get an
assortment cause you have to use the right size.
A manual may be a challenge. We can help with that. DONT loose
any little tags inside that may fall off !!

73 Zeno
LFOD !

[jr_tech]

see pix:

https://www.radiomuseum.org/images/s...ic_2699248.png

https://www.radiomuseum.org/images/s...ic_2699249.png

jr

[old_coot88]

Zero's probably right. From the diagram it looks like it could be a busted dial string after all.

[init4fun]

...

[zeno]

There are 3 pulleys so that points to a broken string. I cant quite read
the manual so thats all I can say
It is a high quality radio so worth the effort.
BTW if you only listen to one AM station you can manually tune
it to that one station.

73 Zeno

[DirtFarmer]

Hey all, I took it to an elderly vintage repairman with decades of repairs under his belt, and it was a busted AM string!

Thanks everyone.

[init4fun]

Originally Posted by DirtFarmer

Hey all, I took it to an elderly vintage repairman with decades of repairs under his belt, and it was a busted AM string!

Thanks everyone.

Thank You for reporting back with the solution


PS, "elderly vintage repairman" pretty much describes at least a couple of us here too....