Motorola 57W
 

First of all, please be patient with me. I'm 17 and just starting out in electronics. I read (more like skimmed, to be honest) several books about electronics and have a decent understanding of the basics. I also have been reading this forum for months now and have watched a number of useful videos on youtube. Now I'm embarking on my first project, a Motorola 57W purchased cheaply from eBay. It is a basic mid-50s 5-tube AM-only tabletop radio which I thought would be a good beginner's project. I plugged it in and it does work which is a nice surprise since it was advertised as for parts or repair. I have a few questions that folks here can probably answer (sorry if any are stupid questions). Four of the tubes are Motorola, of which two I know for a fact are original based on their 1956 date stamps and the other two Motorolas are probably also original. The fifth tube is an RCA replacement with no date stamp, but it has the newer/current RCA logo so perhaps that narrows it down a bit. Does anyone know when they started using that logo? Also I notice several of the tubes have a black blotch on the inside of the glass. I was just wondering if this equates to high hours? I don't have a tube tester, but since the radio works I do conclude all the tubes are good or at least serviceable for now. The underside of the chassis is loaded with paper capacitors, so I won't be running it anymore until those are all replaced. One cap is a huge red one with four wires which, based on Mr. Phil Nelson's site, I have identified as a multi-selection electrolytic capacitor. Does four wires mean I will have to replace it with three separate caps with one shared ground wire? I'm not going to proceed with replacing caps until I buy a photofact schematic, but just wondering. Last thing, the knobs are pretty dirty and one is especially nasty. What's the best way to clean them without causing damage? They're plastic, that's all I know. Sorry this is long and thanks for the help..:)

http://www.videokarma.org/attachment...0&d=1480480050

I was only allowed to attach one image. More can be viewed here :):http://videokarma.org/album.php?albumid=694

The black blotches are called getters and are normal in tubes of any age...During manufacture they use high power to vaporize magnesium or similar reactive metals so they form a coating on the glass. That coating sucks up any remaining/newly freed gas molecules that otherwise would contaminate the vacuum.

BTW a good way to tell if a tube no longer is under vacuum is if the getter turns white.

Typically a 4 wire tubular cardboard lytic has 3 caps with a shared negative, but there are exceptions....The values and wire color code should be on the cap's label...Read it.

You are correct... I twisted it around and the back lists three values: 40mfd 150v red wire, 30mfd 150v blue wire, and 30mfd 150v orange wire. None of these exact values seem to be readily available. I believe the 30mfd could be easily replaced with 33mfd, however the closest I can find for the 40mfd is 33mfd or 47mfd, either seven above or seven below. So I'll probably combine two 22mfd, that would produce 44 which seems acceptable. Thanks.

Another note: Most lytics back then had -50%/+100% tolerance. The set won't care much if you put in a 20uF or an 80....
Higher = less hum, but higher B+ (with higher line voltage it could add to that and make B+ excessive). Lower=lower B+ (which can compensate for higher line voltage), but more hum. There are trade offs, but either way it should work.

Photofacts of that era are in the public domain, so they can be scanned and shared here freely.

https://www.dropbox.com/sh/zobwj67eh...3S4L07Z_a?dl=0

Enjoy!

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RCA used the newer logo, starting in 1969.
The Motorola OEM tubes had red printing at that time, their replacements had green printing.
For 'lytic replacement, I would go with 47,33,33 mfd, @ 160 volts to replace the originals.
For cleaning the knobs, try some real strong cleaner such as Formula 409 and an old tooth brush.

Excellent. Thank you for posting it. I will print it at home after school.

Ordered parts from Mouser. Nichicon brand electrolytics and Panasonic film caps. I bought ten of each value I need in order to qualify for the bulk discount. Hmmm... Looks like I need to start looking for another project to use up the extra caps :scratch2:. Main reason I went with mouser is they also sell the #47 bulb I need for the dial backlight. I looked closely at mine and the filament appears to be open. Later I'll check for continuity with the multimeter just to be sure.

I was going to mention the pilot lamp. If it's not replaced, the life of the 35W4 tube will be shortened. :sigh:

This can happen with Zenith (and other) radios as well. I have an H511 in which the pilot light burned out due to a deformed filter capacitor in the power supply (I had purchased the radio used on eBay, so it may have been sitting in someone's basement, garage, etc., unused, for decades, which could very easily account for the deformed 3-section power supply electrolytic). The radio worked with the burned-out lamp, but the 35W4 ran so hot it would have burned out in short order if I had kept the set on very long.

Replacing the pilot lamp cooled down the tube and the radio worked normally after that. Many AA5 radios used a #47 pilot lamp, placed behind a decorative emblem (as in the Zenith H511 series). The bulb will illuminate very brightly for a fraction of a second when the radio is switched on; when the tubes are fully warmed up, the pilot lamp will glow at normal brightness. VK member wa2ise mentioned in a post here some time ago (I don't recall where that post is anymore) the importance of the pilot light in many AA5 radios. Needless to say, the radio should not be used until the pilot light has been replaced.

True, Jeff. Who knows when this radio was last regularly used or if they were running it with the lamp burned out. Perhaps it's no coincidence the 35W4 is a replacement from 1969 (or newer) whereas all the others tubes are original 1956 Motorolas.

So far I've not been able to remove the old lamp. Either it wasn't designed to be unscrewed or it's frozen after all the years. Did your zenith's light socket look anything like the picture of mine and if so, do you remember how to remove the light? Thanks.
http://videokarma.org/attachment.php...5&d=1480743478

A far as getting the bulb out, it's a bayonet type. Simply push the bulb inward and twist left. Sometimes over the years they get sort of stuck and takes some wiggling it around to get it loosened, but it looks as if it should come out fairly easy. It's nice to see younger guys like you getting interested in collecting and restoring old electronic stuff. Back in those days they were made to be fix and repaired. Some of them have really nice cabinets and are still very good performers. After some practice with this radio, you can get some experience with soldering, replacing caps, wiring, tubes, etc, you will be able to move on to bigger more complex stuff. It's mostly the same technique whether it be a small radio, or a big color roundie console TV. Your radio looks to be in really good shape, no rust, nice and clean. Also for sure change out those white wax capacitors and the black one with strips. The black one with with strips are termed "bumble bee" capacitors. If the volume control is staticy as you turn it, spray it with some electronic contact cleaner. The bumble bee capacitor is a .047 mfd. Most of the time (unless the capacitor has a higher voltage rating) 600 volt capacitors will suffice just fine. The ones in the radio are probably rated at 400 volts, but going higher in voltage is fine. Another place to get capacitors is capacitorworld. They do not have a bulk requirement, and they are quite reasonable. Here are a couple of links that you might find useful.

http://www.bulbconnection.com/ViewSI...FcK6wAod3agB5A

http://www.capacitorworld.net/

Yes the 47 bulb is a bayonet type. As Walter mentioned...push back and turn to the left and it should pop out.

Thank you, Walter. The bulb came right out exactly as you said. Wasn't at all stuck, I just didn't know how to remove it.

I have an appreciation for both older and newer gadgets, but when it comes to quality and longevity, there's no contest. For me, this is an introductory project. I'm looking forward to bigger and better things, but this is my opportunity to gain restoration experience and get to know you guys.

As far as capacitors, thanks for the recommendations. I actually did consider capacitorworld and I really like how simple their website is. Muuuuch easier than navigating mouser. Only thing was they didn't sell the bulb, so I would have had to buy it elsewhere. The site you list wanted to charge me $0.39 for the bulb and $9.99 for shipping. Eh, no :nono:. Radio Shack has them, but way overpriced (typical radio shack) and nowadays the nearest store to me is all the way in Belcaro. But yeah, in the future I'd definitely use capacitorworld and I'm glad someone here can vouch for them. And the bumblebee, is this also what's known as a "black beauty?" I looked at it and at first thought it was an oversized resistor. Wasn't until I got the schematic (thanks again, Wiscojim) that i realized it was a capacitor. It will be replaced soon.