[Nathan Slingerland]

Let the games begin!

This morning I started work on the 37-690 power / amp chassis.

Here's what it looked like fresh out of the cabinet:

[Image: https://farm2.staticflickr.com/1820/4225...8dca_z.jpg]
[Image: https://farm2.staticflickr.com/1831/2912...5b6b_z.jpg]

Yikes - lots of rust, dirt and cobwebs!

Schematic

For those who like to follow along, here's a copy of Philco Service Bulletin No. 267.pdf.

My first step was to review as many previous 37-690 restoration threads on the Phorum as I could find. As usual tons of useful information and photos!

• Ron: http://philcoradio.com/phorum/showthread.php?tid=9676
  
• Kenradio: http://www.philcoradio.com/phorum/showth...?tid=18385
  
• bandersen: http://www.philcoradio.com/phorum/showth...p?tid=4670
  
• thirtiesradio: http://philcoradio.com/phorum/showthread.php?tid=4724
  

Please let me know if I've missed yours.

[Nathan Slingerland]

My first step (after cleaning off all of the cobwebs) was to go over the major components that I could check with an ohmmeter and verify resistances.

[Image: https://farm2.staticflickr.com/1851/4339...d34b_z.jpg]

The production change described in service bulletin has been applied. Two flexible resistors are used to replace the 80 ohm and 325 ohm sections of the Part No. 177 Candohm.
* 33-3027 - 75 ohms
* 33-3121 - 300 ohms

The 3K section of the replacement two-section Candohm is open. Based on what others have found this is not an uncommon point of failure for this set.
I've ordered new 2.2K and 3K power resistors from Mouser - 50W based on Ron's restoration.

The HV windings of both power transformers measure to spec. The same for the rest of the chokes and transformers on the chassis. That's certainly good news.

[Nathan Slingerland]

The next thing I want to tackle is the rust.

My plan is to remove all of the electrolytics, chokes and transformers other than the power transformers from the chassis. That should let me derust more easily with Evaporust Gel.
I'll derust the transformers separately - and then repaint them.

Power Transformers
I removed the tops of the power transformers so that they can soak in Evaporust.
[Image: https://farm2.staticflickr.com/1838/4320...a77a_z.jpg]

Since the weather is warm it shouldn't take too long to derust these.

Electrolytics
[Image: https://farm2.staticflickr.com/1838/4339...988e_z.jpg]

Chokes and Transformers
[Image: https://farm2.staticflickr.com/1899/4339...1570_z.jpg]

Anything removed got bagged up along with hardware and any associated parts and wires that are no longer soldered to anything.
[Image: https://farm2.staticflickr.com/1840/3024...8bae_z.jpg]

I labeled all of the connection points and components so that I can get it back together again:
[Image: https://farm2.staticflickr.com/1842/3024...371a_z.jpg]

Ready for Evaporust
[Image: https://farm2.staticflickr.com/1838/4406...7813_z.jpg]

I covered all of the sockets with tape to prevent Evaporust from getting into them. It should be good to go.

[Kenradio]

Hi Nathan, watching your restoration with interest. My 37-690 restoration went very well and it plays great. It took me around a month to restore it but it was well worth it and luckily for me the cabinet was in excellent condition.   Ken

[Nathan Slingerland]

That's awesome Ken - I wish the cabinet was in better shape as that worries me more than the electronics.
I may try to find somebody locally (or even not locally) with a real spray setup to refinish it.

[Nathan Slingerland]

Chassis Rust-Removal

Today I applied Evaporust Gel to the chassis. That should be much gentler than Naval jelly and hopefully not etch away anything that's not rust.

During:
[Image: https://farm2.staticflickr.com/1815/4231...c811_z.jpg]

After:
[Image: https://farm2.staticflickr.com/1894/4231...eda0_z.jpg]

Making progress...but not there yet. It may take several applications of Evaporust Gel (it did on my 112 chassis).

Tranformer Rust Removal

I did use Naval jelly on the transformers since they'll be painted. Naval jelly does work faster and has a consistency that is a bit easier to work with.

Before:
[Image: https://farm2.staticflickr.com/1890/2918...b55b_z.jpg]

After:
[Image: https://farm2.staticflickr.com/1868/2918...c548_z.jpg]

These also need just a bit more to be rust free. Then I can sand them and repaint.

[morzh]

Lots of unelectronic activity. I hate it.

You're doing great, Nathan!

[Nathan Slingerland]

Thanks Mike!

Yep not many electrons flowing yet.

[Arran]

If the rust is bad enough, sometimes it's worth stripping parts down parts like transformer bells (covers), or chassis, and running them through an electrolysis rust striping tank, quite often it will even take the old paint off. I don't know how far you want to go but you could look into stripping the rest of the power supply chassis down and replating it with zinc.
Regards
Arran

[klondike98]

Watching this ... go Nathan!

[Nathan Slingerland]

Thanks Bob! I'm glad to offer something popcorn worthy.

Arran - thank you for the suggestion on electrolysis rust stripping. That sounds more ambitious than I'd like to get into with such a complex set, but I'm sure the result would be excellent.

[Nathan Slingerland]

While Evaporust is working and I'm waiting on other parts I've started on restuffing the electrolytic capacitors.

In the past I've used terminal strips under the chassis to mount the replacement caps and left the original electrolytics in place for appearance.
I decided that this set really demands that I up my game both for the sake of neatness as well as the fact that there are a lot of electrolytics! It would just get too messy to re-route all of those wires and find space for the replacement caps. Space was an extra concern because I want to use 630V Solen film caps for longevity.

I read over previous posts on how others have done it to come up with a process. I don't think I've seen anyone doing it exactly this way but I was drawn to the idea of using a rivet to attach a solder lug to the case so that no additional electrical connections would need to be made to the capacitor. It also makes a handy way to route the wire to the positive stud.

I'd rather connect to the stud internally but couldn't think of a good way to do that. A solder lug crimped onto the stud internally might work - but I don't have anything like that to try it out.

0. Start

I practiced on a couple of spare electrolytics to smooth out the kinks then started in on part 166 - an 8uF capacitor.

Shaking the can I could tell that this is the 'wet' type and still contained liquid.

[Image: https://farm2.staticflickr.com/1848/4413...3ea2_z.jpg]

1. Drill hole for rivet

This is also useful for draining the liquid before sawing the can. I first drilled a 1/16" hole - then widened it to 1/8" for the pop rivet.

[Image: https://farm2.staticflickr.com/1899/4418...2b44_z.jpg]

2. Cut open can

I used a wire jeweler's saw.

Wrap the can in tape to avoid scratching the can if the saw slips.

[Image: https://farm2.staticflickr.com/1873/4238...8936_z.jpg]

3. Attach solder lug with rivet

Use an aluminum pop rivet to attach a solder lug to the inside of the can.

I used a 1/8" x 1/4" pop rivet from an assortment that I bought off of eBay.

The solder lug I used was RadioDaze LUG8A-10. It appears to be Keystone Part 7313 that you can buy much cheaper from Digi-Key.

[Image: https://farm2.staticflickr.com/1870/4413...ed1b_z.jpg] [Image: https://farm2.staticflickr.com/1867/3032...feda_z.jpg]

4. Make the rivet hollow

Push the head of the pop rivet out using an awl so that the rivet is hollow

5. Connect positive stud

Route a wire from one end of the capacitor through the pop rivet hole to the 'positive' stud of the case.
I used a bit of heatshrink to protect the connection on the bottom of the cap so that it can't make contact with the case.

6. Connect negative case

Solder another wire from the other end of the cap to the 'negative' case solder lug.

[Image: https://farm2.staticflickr.com/1819/4418...1940_z.jpg]

[Image: https://farm2.staticflickr.com/1867/2925...011f_z.jpg]

7. Reassemble

I used a strip of HVAC aluminum foil tape cut to ~1/2" to reconnect the two halves of the outer can. It's important to keep in mind that although the HVAC tape is metallic it's really just for appearances and good adhesion - and does not connect electrically to the can due to the adhesive layer underneath. So the strip needs to be narrower than the clamp holding the capacitor.

[Image: https://farm2.staticflickr.com/1882/4347...337f_z.jpg]

8. Test

[Image: https://farm2.staticflickr.com/1844/3032...8492_z.jpg]

[Nathan Slingerland]

Reading Chuck's article on rebuilding electrolytics I see he has a way to attach to the stud - will try that on the next one so the wire won't be visible.

http://www.philcorepairbench.com/rebuild...trolytics/

[Nathan Slingerland]

I have a question about the schematic from the 37-690 service bulletin (No. 267) and part 152.
Thats Part No. 30-2176, Electrolytic Condenser (8, 10 mfd).

   

When capacitors are drawn this way it usually means that the 'can' part is the negative and the 'stud' part is the positive.
I suspect the schematic is incorrect.

I believe that usually in this configuration the 10uF capacitor would have positive connected to ground., negative common with the other 8uF half of 152 and part 151 (another 8uF cap) all of which connects to the center-tap of the transformer.

Another datapoint is that according to the 1939 Parts Catalog 30-2176 is 'common negative' with leads.
   

(Side note: it is nice to know that the 10uF section is rated at only 10V. There was no way I could fit both 8uF and 10uF Solen caps into the same can!)

[Ron Ramirez]

> I believe that usually in this configuration the 10uF capacitor would have positive connected to ground

That is correct, the low voltage (50 volts, 10 uF) capacitor's positive end connects to ground and the negative end to B- at the transformer center tap, which is the most negative point in the radio.