Magnavox Model FM-43 AM/FM/FM-AFC Radio Issues

[vortalexfan]

Greetings everyone, yesterday I found a late 1950s early 1960s vintage Magnavox Model FM-43 AM/FM/FM-AFC "High Fidelity" tabletop radio at a local antique mall for $25 and it had the typical 60 HZ hum due to bad filter caps, which I was able to replace with modern radial lead aluminum electrolytic caps and then I replaced 2 paper caps (which is all it had in it paper cap wise, the rest of the caps were all of the ceramic disc type).

I powered up the radio to test it out, and the tuning dial was way off on both AM and FM bands, on the FM band one of the local 50kW FM Stations which has a frequency of 104.7 MHz was showing up at around 99.7 MHz on the dial, and on the AM Band the local Gospel Station which is at 1270 kHz on the AM Band was showing up at around 1070 AM on the dial.

I need to do an alignment on this radio, but the only service information I could find on this radio is Sams Photofact 670-6, which I don't have access to, and I would rather not pay the $15, plus tax for a digital download.

If someone on here has an original copy of the Sams Photofact 670-6 that they could scan and send me, I would appreciate it.

Thanks!

[old_tv_nut]

Could it just be a dial string problem? No alignment needed just to get the pointer pointing at the right number.

[vortalexfan]

Originally Posted by old_tv_nut

Could it just be a dial string problem? No alignment needed just to get the pointer pointing at the right number.

I checked that and the pointer goes across the dial from end to end like it's supposed to.

It's definitely an alignment issue.


Because if it would of been something as simple as the pointer being misaligned on the dial string then the pointer would of tried to fall off the end of the of the dial on either end as you got towards the end of the full travel of the tuning condenser and it didn't do that, the pointer stopped right where it was supposed to on either end of the dial once the tuning condenser reached the end of its travel, the stations though didn't match up with where the pointer was pointing on the dial.

[old_tv_nut]

It puzzles me that both AM and FM are off, and in the same way. That still seems like a mechanical problem. Is the amount of physical offset of the pointer the same for AM and FM, or different?

[old_coot88]

Is the big pulley affixed permanently to the shaft, or is there any set screw(s) that would alllow the pulley to be adjusted relative to the shaft?

[vortalexfan]

Originally Posted by old_tv_nut

It puzzles me that both AM and FM are off, and in the same way. That still seems like a mechanical problem. Is the amount of physical offset of the pointer the same for AM and FM, or different?

There was a typo on the initial posting, the AM Band is actually between ~140-240 kHz off from where the stations should be on the dial (this is an approximation because I can't tell where the pointer is actually pointing to exactly on the dial because its an analog dial and I'm not really sure how you tell where exactly the needle is pointing down to the exact 10 kHz marking interval (e. g. 1200 vs 1230 on the dial), but I was guessing where the pointer was at by where it looked like it was at on the dial in reference to the next closest marking.

the FM Dial is off by 4 Mhz by the looks of things and where the strongest local stations are showing up on the dial in relation to where they should be on the dial (104.7 MHz is a local 50kW FM Blowtorch station that covers most of the state of Indiana with many repeater stations, and it was showing on this radio's dial at the 100.7 MHz mark on the dial which is 4Mhz down from where it should be on the dial, and that's where a local country music station should be on the dial called B100 (100.7 FM).

As for the main tuner pulley attached to the tuning condenser shaft goes, yes that pulley does have set screws but they have noot been touched ever (they still have the original thread lock glue on the set screws yet and its untouched, the FM Tuner section uses one of those old Gorler slug-tuned tuner assemblies, and the AM band is the tuned on the tuning condenser.

Also I forgot to mention but the 12BE6 tube (V2 on the tube location diagram on the back of the radio) had been replaced with a 12BA6 at some point in time in the radio's life which I'm not sure if that would affect things in this radio or not (I have since replaced it with the proper 12BE6 tube, but I'm not sure what that tube does in this radio since I don't have access to the Sams for this radio, so for I know that tube being replaced with the wrong tube could of messed up the original alignment and someone may have tweaked the original alignment to make it work with that 12BA6 that was installed in there.

I hope this helps you understand where things are with this radio.

[old_coot88]

It's amazing if the radio worked with a 'BA6 in place of 'BE6, as they are quite different tubes, the 'BE6 being a heptode oscillator/mixer for AM, and the 'BA6 a plain pentode. If it indeed worked, somebody musta been playing with the osc. trimmer.

[vortalexfan]

Originally Posted by old_coot88

It's amazing if the radio worked with a 'BA6 in place of 'BE6, as they are quite different tubes, the 'BE6 being a heptode oscillator/mixer for AM, and the 'BA6 a plain pentode. If it indeed worked, somebody musta been playing with the osc. trimmer.

Yes, indeed, but like I said I don't have access to the service manual so I don't know which adjustments are which on this radio.

[Electronic M]

Generally the trimmer on the Big section of the Variable cap will be AM RF the small section trimmer will be the AM osc. IF cans are fairly obvious (and often have frequency markings to distinguish AM and FM)...Just watch out for a lone FM IF can near the FM detector Those are usually the discriminator and you don't peak tune those.

You say the FM is slug tuned like a Zenith instead of Cap tuned (like most other brands)? If so those slugs are usually on threadded rods that when twisted adjust where they hang/the tuning. The coil with fewer turns will be the Osc and the one with more turns will be the RF amp.

[vortalexfan]

Originally Posted by Electronic M

Generally the trimmer on the Big section of the Variable cap will be AM RF the small section trimmer will be the AM osc. IF cans are fairly obvious (and often have frequency markings to distinguish AM and FM)...Just watch out for a lone FM IF can near the FM detector Those are usually the discriminator and you don't peak tune those.

You say the FM is slug tuned like a Zenith instead of Cap tuned (like most other brands)? If so those slugs are usually on threadded rods that when twisted adjust where they hang/the tuning. The coil with fewer turns will be the Osc and the one with more turns will be the RF amp.

Yes the FM is slug tuned on this radio, but not the same type of slug tuning as Zenith Used, but the old Gorler type slug tune mechanism where it's a small grey rectangular box that has 3 adjustment screws on top and a string that comes out of the left side of it that is attached to the tuner pulley.

I tried adjusting some of the screws on top of that tuner assembly and they really didn't do much to affect the tuning except make the FM band louder.

[jr_tech]

Here is a guy fighting a similar problem:

https://m.youtube.com/watch?v=hL4JMK7Stok

jr

[vortalexfan]

Originally Posted by jr_tech

Here is a guy fighting a similar problem:

https://m.youtube.com/watch?v=hL4JMK7Stok

jr

Yes, just as I thought it was an alignment problem.

I think that guy in that video lives near me because he had the same stations on the dial as I do.

[vortalexfan]

OK so a little update on this radio, I did a full realignment on this radio, and boy was it way out! especially the FM, the AM was also but the FM was more so.

I have a feeling that whoever stuck that 12BA6 in place of the 12BE6 in the radio probably had some howling problems with the oscillator and was trying to fiddle with the controls to make it stop and they were unable to so then they just put it away.

Anyways this radio was supposed to have one of those capacitive line antennas, but unfortunately the antenna hookup lug is missing from the cord so the built-in antenna doesn't work on this radio anymore, has anyone had any luck fabricating a new capacitive line antenna connecting lug for their power cord on their old radios? If so what materials did you use?

Your help is much appreciated!

[Electronic M]

On most sets the cord FM ant coupler is just a piece of sheet metal and some cardboard to protect the cord insulation from puncture.

I've never made this exact piece but I've made plenty of trickier stuff.

Just need to find a piece of metal thick enough to hold a bend but thin enough you can cut it with tin snips or a Dremel cutoff wheel copy the flat shape of one from another radio, file the sharp edges off, then bend it up, stick the cardboard and cord in and press it till it grips the cord well.

[vortalexfan]

I tried to make an antenna in a style similar to the one that's on the Zenith J733 Clock Radio which was using a rubberized metal cable clamp that was riveted to the cord along with a 6" length of wire and I hooked that wire to the internal antenna terminal on the back and left the int. antenna jumper in place but it doesn't seem to be working right.

Any ideas as to what's going on with my setup, and why its not woring?