Zenith M730 Part II

Well it's done. I got all the caps replaced. I was not able to re-stuff the old multi section cap and ended up putting the new caps under the chassis. Here is a pic with all the new caps. The orange pillow shaped ones and the large striped cans. I forgot to take a picture of the replacement for the selenium rectifier, but you can see most of it in the lower right corner. I installed 2 33ohm 10 amp resistors (in series) in front of the 1n4007 diode to lowr it's voltage output to 130vdc about 5 volts lower than it should be but that is within tolerance.

The only issue with the radio after I finished recapping is that I accidentally hooked the AM loop antenna to the FM antenna connector and Vice-Versa. once that was corrected it works just fine, no re-alignment needed.

Cleaned and lubed all pots and bearings.
Cleaned the FM/AFC/AM switch.
Cleaned most of the Cadmium Sulphide off the chassis.
Cleaned the dust and spider webs out of the case.

Implemented the following safeties:
recapped (of course).
replaced selenium rectifier with a silicon diode.
larger surge resistors
polarized plug
rear interlock keyed for the polarized plug.

1 tube tested bad on my tester but I am debating whether to replace it at this time.


Zenith M730

So I accidentally bought a radio on ebay. I was looking for a radio that we had when I was a kid and thought that this one was it (as best I could remember).
Turns out it was not, the radio we had was one of these:
Anyways... there was an option to "make offer" I never did that before on ebay and figured it would either not accept it or would take a day. So I offered $15, it instantly came back and said offer accepted pay now! Whoa, wait a minute! Then I looked at the shipping and that would be about $30 THIRTY DOLLARS! Sigh.

Well I got it the other day and hooked it up to my dim bulb tester:
And the bulb did not light (which is good). The radio worked (both AM and FM) even though the auction said the FM did not (bonus). The case is in really good condition and may only need some polishing. The knobs are worn but not enough to replace them.

So now I am in the process of electrically refurbishing it. Here the list of things that need to be done:
Replace all the paper capacitors (3).
Replace any weak tubes.
Replace the potted electrolytic 3 section capacitor (or re-stuff it).
Replace the Selenium Rectifier with a silicon Rectifier (and attending passives).
Fix the radio so that it cannot be plugged in (easily) with a hot chassis when the radio is off.
Add a fuse.
And anything else I can think of that will keep the radio from accidentally killing someone.

When I opened the radio it was only slightly dusty inside, especially for a radio that is around 60 years old. As far as I could tell it was all original, or if any repairs were done, they had been done with factory parts. The one scary thing I noted was that some of the metal parts were covered with a yellow dust. I did not know what this was and this made me a bit leary of it. I avoided touching it and cleaned it with denatured alcohol after blowing the chassis off outside. Later on I googled "yellow powder vintage radio" and found out that it is cadmium sulphide. YIKES! seems some of the parts are cadmium plated. So I cleaned it some more with vinegar (neutralizes the CS and removes it) and denatured alcohol until most of it was gone. Then wiped down my bench and thoroughly washed my hands.

here are some pics:
The selenium "Kill you in your sleep" rectifier.
One of the paper "burst in to flames" capacitors.
The front of the chassis with some of the Cadmium "give you cancer" sulphide.
The underside of the "one slip and you're electrocuted" chassis.

So why am I refurbishing a "working radio"? Because it's a death trap. I am going to make it a slightly less "deathy" death trap. because I have never done it before, and because I can.

What I have done already:

added quick disconnects for the AM antenna and the FM antenna lugs, so you don't have to un-solder them to open the back of the radio.
Opened the 3 section capacitor (smelled like band-aids), cleaned it out and prepped it to possibly receive the modern caps I ordered (if they will fit), otherwise they are going under the chassis.
picked up the 1n4007 diode.

Stay tuned.


Sansui Model 7070 Thrift Store Find

A couple of weeks ago I was at a thrift store and ran across an old radio shack scanner. I attempted to see if it worked and using an ac adapter I found at the trift store I went to the testing table to plug it in. There was some old guy just standing looking at something on one of the shelves. I said excuse me and plugged the scanner in. It did not work. Then I noticed another scanner exactly like the first (even down to the missing battery cover). I tried that one and it did not work either. Then I noticed this:
It was on the shelf below and I went to pick it up. The old guy taps me on the shoulder and says "I'm checking that out". "I'm sorry, what?" says I. "I'm checking out that stereo" says he. "Oh, I did not know" says I. Not knowing what it was I wandered around and kept a close eye on it as it was very heavy and looked like it was from the 70's. Heavy is good when it comes to stereo's, and this one weighs about 40 pounds. Anyways... he worked on it for another 5 or 10 minutes then walked off, having not got it to utter a sound. I immediately walked over and hooked up a random speaker I found near by and fiddled with the knobs until I moved the one that was for the speakers from "off" to A and BLAM! sound. I turned it off again and took it straight up to the cashier. I got it for a VERY good price.

I took it home and hooked it up to a pair of speakers and it worked just fine, except that 5 lights did not work. when I opened it up to blow the dust out and check for bad capacitors and any scorch marks I tapped the lights and 2 of them started working again. leaving the middle dial light, the needle light, and the right light in the right channel power meter. I looked it up and found that it is a relatively high end stereo for the time it was made. There was one on ebay in cosmetically better shape and with all the lights working that was going for more than $200. So I cleaned it up a bit video taped it working. It sold yesterday for a lot more than I paid for it.
The one problem is that it sounded so nice I regret selling it. Oh well, hopefully the guy who bought it will enjoy it more than I would have.