magnavox fm tuner wont tune below 93 mhz

[drh4683]

I have a 1963 magnavox am fm phono with color tv console. Everything works perfect (even the tv!!) except for the FM which works but has a problem. FM will not tune correctly below 93 mhz. It will almost be like a very strong station takes over between 93 and down past the end of the dial to 88 mhz. I receive 90.9 mhz way at the end (88), and it spreads up to 91 as if the AFC is on (which it is not). There are stations down at 88.3 that I cannot receive, even if I adjust the oscillator on the fm tuner. It is a "Gorler" brand tuner mounted on the magnavox receiver chassis. Not sure if the oscillator tube is the problem or what. Any help is greatly appreciated! Thanks-Doug

Try replacing the oscillator tube, and check to be sure the variable capacitor plates are fully meshed when the dial pointer is at 88 MHz (could be dial cord slippage).

Bill,
Are those things called air caps? I had a Heathkit antenna tuner that had kidney shaped plates. I noticed something similar in my dead Fisher. Also, that tube you mentioned is a reference tube as to frequency? Sort of a guide tube that resonates at a certain freq? Certain concepts are beginning to return from my uh...youth
thanks,
md

[Kamakiri]

I was thinking that you might check for a slightly bent tuner gang....check for a dead short between the tuner plates at the point that it won't tune stations.

Originally posted by millerdog
Bill,
Are those things called air caps? I had a Heathkit antenna tuner that had kidney shaped plates. I noticed something similar in my dead Fisher. Also, that tube you mentioned is a reference tube as to frequency? Sort of a guide tube that resonates at a certain freq? Certain concepts are beginning to return from my uh...youth
thanks,
md

MD,
The caps are called "air variables". The tube is not a reference tube, it is the actual oscillator that generates the local injection frequency to mix with the incoming signal, developing the 10.7 MHz IF. It may be labelled on the tube placement chart as "oscillator/mixer" or "converter" (on pre-war radios it is called the "first detector"). On post-war FM radios the oscillator operates at 10.7 MHz above the dial frequency, so as the dial tunes from 88 to 108 MHz, the local oscillator tunes from 98.7 to 118.7 MHz. It is the difference beat frequency between the station signal & local oscillator (generated when they are mixed) that provides the 10.7 MHz IF signal.

Check!
thanks Bill,
md

[Charles Vesser]

I had one of those Magnavox radios in for repair last year and liked to have never figured why it would not tune on the low end of the band.
The problem was the DIAL LIGHT was burnt out. I replaced the dial light bulb and it fell right in line. Your's may have the same problem, or it could have the wrong bulb in it.

[kc8adu]

i have seen a scheme like that where the bulb is part of a zener regulator.
funny this came up because a neighbor just tossed a garrelli moped and i got it.they said that 3 shops had thrown parts at it and still no go.
the cure?
replace tailight bulb.
the way the mag is set up you get no spark if the running light fil is out.
tailight burns out you push it home

[vinyltocdr]

dear sir,

try checking/replacing the very small (in value, not physical size) capacitors around the oscillator tube, tuning gang, and in the oscillator circuit.

i had the same experience with a very nice Zenith 1950's radio years ago. it gave me fits until i replaced a tiny capacitor in the oscillator circuit. it received around 99 to 108 megs. below 99 megs, i could not get anything and there were strong locals down there. no matter how i adjusted the oscillator coils for the low part of the band (92.5) and the high part of the band (106.5), <99 megs was not received.

hope this helps.

steve