[mikethedruid]

Today I removed the chassis and speaker from my 37-61 cathedral radio I just bought. I was pleasantly surprised to see that the chassis seems not to have been worked on since the 1940s or so. The only repair I can find is a replacement electrolytic soldered across one of the old filter caps. Looks like an excellent candidate for complete restoration.The speaker cone was complete toast, but the spider at the center is fine, thank goodness, so I am going to just order a cone and try re-coning it myself. There is a great YouTube video showing how to do this. Another relief I found is that all the wiring inside is cloth covered and in excellent shape. This should be a fun project !

[mikethedruid]

Today my 8 inch speaker cones arrived from MAT Electronics, and I re-coned the speaker. It was actually fairly easy because the original spider and voice coil on mine was perfect despite the rest of the old cone being in shreds. All I had to do was trim a tiny bit from the outside of the cone mounting edge so it would fit in the frame. Then I carefully glued the original spider / voice coil assembly to the very center of the new cone using 2 part, 5 minute epoxy. One must be very careful to center the coil in the center hole of the cone, inserting it through the front of the cone. Once the assembly was centered well and beginning to stiffen, I let it dry suspended on a pencil standing straight up, with the point through the center screw hole of the spider, so that gravity would let he cone weight hold it on the spider assembly. Once the voice coil had set up to the cone, I then reassembled the cone into the speaker frame, and glued the outer edge of the suspension to the edge of the frame, again using 5 minute epoxy. One must keep going back and making sure the suspension glues down well all the way around, but eventually it will. I do notice that the speaker suspension foam is a tiny bit higher than the edge of the frame, so I will have to make 1/4 inch spacers for the 4 mounting screws.  I will have to wait now until the radio is all fixed to see how it sounds. My process was similar to this guys, but with less headaches...  https://www.youtube.com/watch?v=H023zMrYDTU  .

[mikethedruid]

Today's project was to remove the shadow mask and light assembly for the dial, and to take a LOT of before pictures of the chassis. I then removed the only mod I can see, a 1940s or 50s electrolytic soldered across one of the old filter caps. Here are a couple of pictures. Pretty dusty on the top, huh ?

[Image: http://40.media.tumblr.com/8638be4ba51c5...1_1280.jpg]

[Image: http://41.media.tumblr.com/9027ee0486d69...2_1280.jpg]

So, that's it for today, stay tuned for more excitement.

[mikethedruid]

Today's project was removing the tuning sub chassis from the main chassis. I carefully desoldered each wire and labeled it. and recorded where it had come from. Fortunately there were only 9 of them. The mounting rubbers are pretty shot, but I have seen some repro ones that I think will work with minor modification, but that is a long way off yet. Right now I have to get things cleaned up and recapped and resistored. Here are some pics...

[Image: http://36.media.tumblr.com/f5e7a6f86a121...1_1280.jpg]

[Image: http://41.media.tumblr.com/a4bd3eca4e9ab...2_1280.jpg]

Stay tuned for more excitement !

[mikethedruid]

Latest electronic work, I put together a parts order, and I cut open my first electrolytic, the one from the tuning section. Interesting interior. They apparently used the outer can as one plate of the condenser, had a perforated insulator within that, and had a set of folded up aluminum vanes inside that insulator connected to the center contact for the other plate, with the electrolyte solution filling the interior of the can. Mine was still full. I wonder if it was still working ? Of course, now we'll never know; but, rather than risk the transformer, I am just as glad to do the preventative work, and never know.

[KCMike]

  Keep us posted on your progess. Always appreciate someone taking time to post their work.
You might look at renovated radios web site for chassis mounts. They mention that the 37-610 will fit but are a little large.

[mikethedruid]

Thanks, Mike, I already got the mounts from them. I think a little judicious use of sandpaper will make them fit quite nicely without any excessive squishing; one does want a BIT of squishing with rubber mounts, after all.

[mikethedruid]

Things are progressing nicely. I have reached the point where I am dealing with the bias resistor, the 3 section candohm. Here is a link to the schematic. The bias resistor is number 43.
http://www.nostalgiaair.org/Resources/208/M0013208.htm
From what I can see, the high voltage current through it would be a max of 70 milliamps, or .07 amps, as that is the rating of the HV winding of the transformer. The resistor is a total of 245 ohms. Using power equals current squared times resistance, I make that to be, 1.2005 watts. If I use 2 watt resistors for each of the sections I should be golden, I figure. Am I figuring right ? What have others used in this case ? Advice will be appreciated.

[mikethedruid]

Actually, I figure I REALLY only need 2 watt for the 202 ohm section, the 8 ohm section and the 35 ohm section could be 1/2 watt, which, of course, would be a cost saving. Again, using I squared R. Looking at the schematic for the 37-60, it used the same bias resistor. What have others used here ? As I said, advice appreciated before I plunge ahead.

[klondike98]

Good progress!!

[mikethedruid]

What led me up to the bias resistor was I just rebuilt C44, the electrolytic with the isolated ground which connects to, you guessed it, the bias resistor R43, as well as the center tap of the HV winding. I am slowly getting the power side of the chassis rebuilt, all the caps and resistors replaced, no micas so far. I removed the bias resistor to get at the 6F6 to replace the various parts attached to it. It is still connected until I figure out exactly what I want to do to replace it. Right now I figure a 200 ohm 2 watt, a 10 ohm 1/2 watt, and a 33 ohm 1/2 watt should be close enough for government work. As I asked before, what have others used in their 37-60 or 37-61 projects ? Alternatively, does anyone know the tolerance on the candohm bias resistors? Not the round one shown in the diagram, but the flat kind in the later chassis, after the bakelite block change outlined in the notes. My guess is 20%, but, it being the fix on the bias of several stages, I would like to know more precisely. If it is 20% I will be fine.

[mikethedruid]

The 10 ohm and 33 ohm 1/2 watt resistors I have been waiting for finally came in. The 200 ohm 3 watt I ordered came in earlier. Today I wired them all to a 4 lug terminal strip, and replaced the bias resistor, and finished the wiring and parts replacement in that corner.
[Image: http://41.media.tumblr.com/75713908861c8...o1_500.jpg]

Next I have to replace one last electrolytic on that side of the chassis, the last of the three. I mentioned earlier that I was thinking of replacing the tone control switch / on - off switch with a proper tone control and switch earlier; well, it seems someone beat me to it many years ago.
[Image: http://36.media.tumblr.com/bf08af464f86c...6v_500.jpg]

That will be what I look at tomorrow, to make sure it is connected safely and properly so it will work well, and make sure the pot is working well. After that I will rebuild that last electrolytic, and then move on to the long terminal strip on the other side of the chassis, desoldering wires and parts, replacing the parts, and putting it all back. Stay tuned for the continuing adventure...

[kiwi_steve]

I'm enjoying this thread, I have one of these to do in a tombstone cabinet at some point... nice to see what I will have to deal with once I brush out the rat droppings, dirt and walnut shells  Keep up the good work...

Steve

[mikethedruid]

Just a little note on rebuilding electrolytics. Some people pull the aluminum center contact post from the base and replace it with a brass screw when rebuilding because they have problems soldering to the aluminum. I just use the aluminum center post with the aluminum fins removed, and cut down to about 1/2 inch above the rubber insulator. I sand the surface of the stub well, and immediately paint on some of the liquid flux I make by dissolving violin rosin in some rubbing alcohol. This helps keep the aluminum from oxidizing which is why it is hard to solder to. The aluminum will begin to oxidize immediately as soon as its clean surface is exposed to air. The liquid flux coats it and minimizes that. I also use an old fashioned Weller 100-150 watt gun, not a pencil. Pencils are fine for solid state work, but for most of the old fashioned chassis work, I prefer the Weller gun. For this application it is very necessary, one needs the heat. Heat the contact until the solder will flow well. Keep rubbing it when it is melted, and it will begin to stick to the aluminum well as it fuses with the surface molecules of aluminum. Once the center post is tinned this way, you can just wrap the + lead from the replacement condenser tightly around the tinned area, and solder as usual.

[mikethedruid]

I looked more closely at that tone control when I pulled it to clean it. I would swear it is something original, were it not that I have not seen that mentioned in the revisions. Do any of our Philco experts know if the factory ever used a 1 MEG pot in this position, connected so it went between where condensers 40 and 41 meet at one terminal of the switch type control, and ground, the other connection of the control ?
http://www.nostalgiaair.org/Resources/208/M0013208.htm
(the schematics for reference)
It looks like it may be a very workable circuit. I'll be interested to see. It seems to be an audio taper pot.