[Ron Ramirez]

I have a rough looking FM-50-B FM tuner, from which I had already robbed a couple parts for last year's Christmas project - a Fisher 100-T Coronet tuner/preamp.

Looking at it sitting in the garage over the past few months, I decided that while I am waiting for mica capacitors for my RCA 6T2 project, I would see if I could get this FM-50-B going.

It may be a bit of a challenge since I don't have a schematic for it. But we'll see.

Photos later.

[Ron Ramirez]

Photos.

[Image: http://philcoradio.com/images/phorum/FM5...0B_001.jpg]

I do have the front panel, which cleaned up nicely...but no knobs.

[Image: http://philcoradio.com/images/phorum/FM5...0B_002.jpg]

Problems:

The chassis looks pretty rough with several rust spots which may (or may not) have been made by Mickey and Minnie.

The dial cord is broken and the pointer is MIA. I'm pretty sure I have a pointer, though.

The dial lamp holders (upper and lower) for the left dial lamp are missing. I'm hoping I have suitable replacements in my parts stash.

I had previously removed the FM limiter coil and ratio detector transformer. I started to use the ratio detector transformer in my 100-T Coronet tuner/preamp last Christmas, but as it turned out it would not work with that transformer so I ended up reinstalling the original. I think I used the limiter coil and ratio detector in another project (an FM-100-C which I restored and later sold).

At the same time I removed those coils, I also removed the WX multiplex decoder for another project which never happened so it will get reinstalled in this chassis once it has been recapped.

---

I had already installed the FM limiter coil (but had not yet wired it in) when I took the photos above. I then installed the ratio detector transformer and wired both back in as they should be. This limiter coil and ratio detector transformer came from a Fisher Ambassador V tuner (680-T chassis). Comparing these to the coils in my good FM-50-B, the part numbers of each are the same as those used in the FM-50-B so we're good there.

Next job: to install a terminal strip and four diodes to replace the original selenium rectifier, along with a 100 ohm dropping resistor in series with the B+ output.

[Nathan Slingerland]

Looks like a great Christmas project Ron.

Would the FM-50 (mono version) service manual help at all?
https://elektrotanya.com/fisher_fm-50_fr...nload.html

[Ron Ramirez]

Thanks, Nathan. I actually have that one (I have a rough FM-50 out in the garage too...trying to decide whether to fix it up, or not). I'll take a look at it. Obviously the FM-50 schematic will have no MPX detector but might have some useful info if it doesn't work upon initial power up.

This evening, I accomplished the following:

* Replaced the selenium rectifier with a terminal strip and individual 1N4007 diodes. I threw the old selenium rectifier in the trash; it made a sound as it hit the bottom of the can, so I know it was bad.
* Replaced the axial 20 uF, 250V electrolytic with a new Nichicon axial 22 uF, 350V.
* Replaced the death cap with a new X1/Y2 safety cap.

Still to come: Replacing two 0.1 uF dog turd caps with new yellow film, and the 8 uF axial electrolytic in the ratio detector circuit. Then comes the MPX decoder, and restuffing the electrolytic.

I won't finish it tomorrow. Probably sometime in January.

[Ron Ramirez]

Replaced the old 0.1 uF dog turd caps with new yellow film. Discovered those were my last two 0.1 uF caps. Time to restock. (I wish I had realized that when I made my Just Radios order.) Going after the 8 uF electrolytic in the ratio detector circuit next.

[Ron Ramirez]

So I replaced the 8 uF electrolytic late morning on Christmas Day.

Today, I returned to the FM-50-B. I recapped the WX MPX decoder and reinstalled it in the tuner.

Then I removed the main electrolytic capacitor can (four section 40 uF), only to find that....I have no 40 uF electrolytics in stock.

So this one will be set aside for a while. I'll order some electrolytics and on the next "good" weekend, I'll restuff the can, install it and we'll see at that point if it works, or not.

[Ron Ramirez]

Parts arrived from Mouser today. Since my chemo was delayed another week I will restuff the electrolytic can this weekend and restring the dial cord. Then we shall see if it works.

[Ron Ramirez]

Restuffing a Twist-Lok Electrolytic Can

Removal involved not only unsoldering and removing several wires and components, but also unsoldering two of the four mounting tabs from the chassis.

Then the can had to be (carefully) cut open at the bottom end so that the insides could all be pulled out.

Once that was done, I installed four new United Chemicon electrolytics which are not only skinny so they fit well, but also have a decent ripple current rating (440 mA). Rated at 105 degrees C and a maximum life of 12,000 hours.

Here's how things looked with the new electrolytics in place and ready for re-installation in the can:

[Image: http://philcoradio.com/images/phorum/FM5...0B_003.jpg]

Once everything was back in the can, I carefully rolled the lip back over the outer insulator to hold everything in place.

[Image: http://philcoradio.com/images/phorum/FM5...0B_004.jpg]

Finally, the can was reinstalled on the chassis and everything hooked back up.

[Image: http://philcoradio.com/images/phorum/FM5...0B_005.jpg]

The added 100 ohm resistor is in series with the output of the new silicon rectifiers connected as a bridge, to take care of the higher voltage from using silicon in place of selenium.

Next jobs: To carefully clean the dial, add a pair of dial lamp contacts for the left side of the dial (which are currently missing), restring the dial cord, add a pointer, add a set of tubes and try it out.

[Nathan Slingerland]

That restuffed can looks great Ron!

What kind of tool did you use to cut open the twist-lock?

[Ron Ramirez]

A box cutter knife...cutting away from me, not towards me. If you are really careful, once you get started cutting the lip, you can use your box cutter knife almost like a saw, cutting the lip away. The important points are to take your time and not get in a hurry...and to always cut AWAY from you Count on replacing the blade when finished.

At first I tried grinding the lip off with my Ryobi "Dremel" tool, but I found it easier and quicker to just cut the lip with the box cutter knife.

I've done twist-lok cans in several Fisher tuners in this manner now, so it is becoming sort of easy. One of these days when I get to my Fisher 500-S and 500-B receivers, I might restuff their cans instead of getting the Hayseed Hamfest replacements as I did with my TA-600.

[Ron Ramirez]

I forgot to mention something:

Inside the Twist-Lok cans are two phenolic insulators with a thick rubber insulator in between. The terminals go through one phenolic insulator, the wire leads go through the other one (and through the rubber insulator as well).

You may be wondering how do I have enough lip left on the can to be able to crimp it over again?

Simple - eliminate the rubber insulator and you have enough aluminum "lip" left to recrimp the can.

[Ron Ramirez]

The dial glass has been (carefully) cleaned. Do not use any wet cleaners on the inside (reverse painted) of the dial glass! You can use your favorite window cleaner on the outside (non-painted) side of the glass, but be careful to not let any of it get on the reverse side!

I lay the glass on a folded towel and then clean it.

So what do I do about the reverse side?

Simple - I breathe on the glass (exhale with mouth) in one spot and then gently rub off the minute amount of moisture that your breath leaves behind. Repeat for the remainder of the dial glass. Doing this is usually a "good enough" cleaning and if you're careful, none of the reverse painted graphics will be harmed.

The next job was to restring the dial cord. That was a major hassle! But it's done, and a dial pointer has been attached.

Then, I "borrowed" the tubes from my other Fisher FM-50-B and installed in this tuner.

I connected an audio cable from this tuner to the AUX inputs of a receiver I have next to my workbench.

When I first fired it up, the tubes lit up but - nothing.

Something told me to wiggle the tubes. After doing so, I could barely hear a station but that was it.

So I wiggled the tubes again and...

Success.

[Image: http://philcoradio.com/images/phorum/FM5...0B_006.jpg]

It works. IN LIVING STEREO.

The 1st IF tube socket is the worst offender. I'll need to clean the tube sockets, focusing mainly on that socket.

Other things to do before it is finished:

• Clean the rust spots.
  
• Align the tuner.
  
• Find and attach four rubber feet. (I have the rubber feet, but I may need to find some suitable 8-32 screws for them.)
  
• Install two LED dial lamps.
  

[Ron Ramirez]

I have some rust remover made by Permatex, and I tried it on the FM-50-B chassis. It didn't work very well. I'll end up buying some Evapo-Rust Gel and trying again at a later time.

Rubber feet now applied to base, base reinstalled on main chassis. I went ahead and reattached the front panel but it will have to come off again when I convert the dial lamps to LED.

It still needs a set of tubes, and an alignment. Plus, I still need to clean the tube sockets - especially that 1st IF socket.

It's going to be set aside for awhile. Next chemo session is Wednesday, so no radio work this coming weekend. At least I know it is working.

[Paul Philco322]

Wiggle and wiggle, sounds so technical. It is the beauty of this hobby radio and electrical theory and then it sometimes comes down to a wiggle or prodding a wire with a pencil eraser! Best hobby ever....................

Good luck with the rest of this job.