Old Midwest 11-36 radio

[EKDENTON]

I wasn't sure where to post about this radio. Hopefully administrator will check and move if needed. I was given this old Midwest radio. Apparently is was working the last time it was turned on but that was many years back. Midwest did not have model numbers so the 11-36 stands for 11 tubes built in 1936. I was able to find the schematics for it at radiomuseum.org. I think I would like to restore this radio to working condition. I pulled all the tubes out and stored them while I do some cleaning and visual checking. Cleaned out some of the woolyboogers, dead spiders,  and dust. I think I should change the capacitors but I can not find 8uf and 12uf can caps in 450v for direct replacements. Some of the caps inside I do not recognize because they are so old. paper, oil and wax? some are polarized so what type will be good replacements for these caps? The resistors are rectangular with painted dots. I will have to research those to see what the color codes are but hopefully I don't need to change any. There is a huge choke that looks like it has been added at some point with a wire soldered to the ac in socket .... I cant tell if it is actually connected to voltage or just there because there are some solder tabs on the outer edges of that socket. the other end of the choke wire go to just one of the 6K7 tubes. That choke is not an original part. 

[EKDENTON]

After pulling the chassis and tubes I realized it has 14 tubes so It is a 14-37 instead. Pre WW2.

[EKDENTON]

Anyone know what the best capacitors for a radio like this might be? And where to look for them? They all look polorized

[sluckey]

If it's over 1µF, use polarized (probably electrolytic). If it's under 1µF, use non-polarized.

[PRR]

0.05uFd etc radio caps have "outside foil" marked. Unlike in audio (where it makes little/no REAL world difference), in a radio the outside foil should go "right way" to cause minimal detuning of RF circuits.

The 4-8-12-16uFd cap series is very old. And were expensive, so sometimes barely-adequate. Use 10uFd, 20uFd, 22uFd as convenient. New caps are much smaller and can be hidden inside the old cans.

Ask if you really need a radio? You already have 13 radios around the house, cars, and attic, plus your cellphone. Maybe you only want to revive the Audio (and Power) parts and jack a boostered guitar into it.

[EKDENTON]

Thanks guys. Not that I need a 30lb tube radio in the house LOL. But it would be fun to restore something built 20 years before I was born. It is actually an all band so it should pick up alot more than just AM and FM. Who knows maybe if i can get it back into good working order I may sell it. PRR That is interesting that you mentioned  about the outside foil of the caps.


The new type caps are not marked so at first thought it may not matter which way they go, but they do have an outside foil. i found a post in another forum about how to find the end with the foil using a signal tracer and a scope.


 It will make a difference which way they go. Here is the post i found:


Thanks Tom,I tried some new metallized film caps with the signal tracer and a scope. These have no mark for the outside foil. When connected one way, grabbing the body of the cap with my fingers makes no difference. When the connections are reversed, a significant amount of 60 Hz is injected, enough to be plainly audible in the speaker. So indeed these caps do have an outside foil, which the manufacturer is failing to identify. Interestingly enough, the smaller the value of the cap, the higher is the injected hum voltage. I suppose this is due to the larger values bypassing more of the hum to ground.<P>I know this makes a difference in some circuits, because a radio I had developed a supersonic oscillation in the audio stages after being recapped. When the audio coupling caps' connections were reversed, the oscillation stopped. The connection that worked was with the outside foil connected to the plate of the preceding stage. I just looked at an old chassis that has not been recapped, and the caps are all meticulously oriented so that the outside foil goes to ground on bypass caps, and to the plate on coupling caps.

[EKDENTON]

I tried to get the Mallory caps to do what the guy in my previous post did. I tried frequencies at guitar amp up to UHF frequencies. I put a range of amplitude signal through the cap. I had two of the same caps with one connected 180 opposite the other. One scope channel on each so I could compare at the same time. Touching the yellow body  of the cap had made no visible signal change or noise in the signal on the scope.

Then I found the Sozo brand are marked like the old caps. Hmmmm.