Hi Everyone,

This is my first post in this forum. On my way back to work from lunch I popped into the thrift store. I found a nice old Zenith radio. They researched it and were asking what it's worth, or maybe even a little more. But I thought it was really cool so I bought it. I haven't had a chance to take a close look at it, but it's a very neat radio. Can't wait to play around with it.

This is just a picture I found on the interwebz. Mine's not quite this clean, but I think it will clean up well.

Take care,

Ed

These are great little radio's. They put out pretty decent sound for the size. This particular chassis and slight variations of it were used from the late 40's all thru the early 60's by Zenith as it was a good performer, reliable and easy to service. Dont be fooled by its plain Jane appearance as you will definately be surprised by its performance. I've picked up stuff on mine that i was never able to on other radios i have from the same era. You did good Ed!
-Tony

Hey, that radio looks familiar.

http://www.audiokarma.org/forums/showthread.php?t=136531

Murray

I plugged it in, turned it on and got noting. Then I remembered. Doh! Tubes. It has to warm up. A few seconds later, sure enough, it works like a charm! AM and FM both working well.

Skippy, mine isn't quite as clean as yours. I think I'll probably have to refinish the wood work, but yes, it's exactly the same radio!

Even my wife thought it was cool and didn't give me a hard time for dragging it home.

Take care,

Ed

A couple of pics...

Looks pretty good. The front panel will come completely out as it's just screwed to the cabinet, from the inside. A little tricky to get to the screws but it can be done in a few minutes.

Yours has a little more fancy grill cloth than mine.

Murray

Zenith must have made 3 blue million of that style of radio from the late '40s til the '60s...They had the formula right-those guys are usually good performers. I have a blonde 1st cousin to that one, plus a BUNCH of the earlier "K725" styles...

I read a couple of things that said there were indeed a lot of them made and that they're still reasonably easy to find. I checked e bay and prices seem very reasonable and most are advertised as working well, so they must be pretty robust.

I removed the back for a peek inside. It's not too bad. The tubes all look pretty clean and everything looks to be in order. There is some dust collected in there, but it should be easy to clean up. It will be a fun project. But my history finishing wood isn't too good. I may have to practice on something else.

I really like the radio and my wife has agreed to let it live in the dining room. NPR is on AM here and she loves to listen to it all weekend. But the AM on our modern radios sounds horrible. I tuned it in on this little gem and it sounds sooooooooo much better!

Like Sandy, I have several of these, different flavors.

The sound is really amazing, and at 1/10th the cost of a Bose. And, as you're finding out, a reasonable WAF!:thmbsp:

They're actually acceptable in the living room or kitchen.

In it's new home!! I cleaned it a tiny bit and put some butcher block oil on it. Shined up pretty good and helped minimize the rough spots in the finish at least a little...

Murray, the thread about your radio talks about several items you replaced. This was a tiny bit over my head. Did you replace the blue thing? I think this radio will likely be used daily. I'd like to get it into tip top shape. I can solder and such pretty well. I'm sure I have the skills to put it all together, just not the knowledge of what exactly to do...

have the plastic version of the same radio made in 1959

Murray, the thread about your radio talks about several items you replaced. This was a tiny bit over my head. Did you replace the blue thing? I think this radio will likely be used daily. I'd like to get it into tip top shape. I can solder and such pretty well. I'm sure I have the skills to put it all together, just not the knowledge of what exactly to do...
I replaced all the axial caps underneath and one that's on top where the tweeter connects. The new caps are all Illinois Capacitor, 630v. The little "black beauty" striped cap that was on the left connected to the volume pot is .01 µf.

I powered it up and got some nice sound on AM but nothing on FM as I didn't have the antenna connected (hopefully that's the problem).

I'll probably change the blue thing this weekend although I'm pretty sure I don't have a larger value resistor (one of they guys in my thread suggested a 33 ohm to change the 22 in place). And, I did get new caps to replace the multi section cap. Nich 160v,100 and 47 µf.

Murray

I replaced all the axial caps underneath and one that's on top where the tweeter connects. The new caps are all Illinois Capacitor, 630v. The little "black beauty" striped cap that was on the left connected to the volume pot is .01 µf.

I powered it up and got some nice sound on AM but nothing on FM as I didn't have the antenna connected (hopefully that's the problem).

I'll probably change the blue thing this weekend although I'm pretty sure I don't have a larger value resistor (one of they guys in my thread suggested a 33 ohm to change the 22 in place). And, I did get new caps to replace the multi section cap. Nich 160v,100 and 47 µf.

Murray

I may have a look in mine this weekend. It is working perfectly and I can get ok FM with no antenna, but I live in the city. AM is wonderful.

I joined an antique radio forum to ask questinons about what to do for it to keep it happy. They suggested some caps like you're talking about, but advised that if the selenium rectifier looks to be in good shape and the B+ voltage checks out that it's probably good for another 20 years. They also said the health concern is largely overstated. So for now I'm going to leave it. I'll just check the caps and enjoy it!

I can't believe how much better AM radio sounds on this thing than our modern radios. Even my stereo systems are harder to listen to. AM has always driven me nuts, but I can listen all day on this thing.

...I powered it up and got some nice sound on AM but nothing on FM as I didn't have the antenna connected (hopefully that's the problem)...

Murray

Murray, I may be incorrect, but I believe that the AC cord functions as the FM antenna, so if all you're getting is silence, you may have further issues.

Murray, I may be incorrect, but I believe that the AC cord functions as the FM antenna, so if all you're getting is silence, you may have further issues.

The power cord should be going through a small metal clip that attaches to the antenna lead.

Murray, I may be incorrect, but I believe that the AC cord functions as the FM antenna, so if all you're getting is silence, you may have further issues.
Yeah, I didn't have that little clip connected.

Anyway, it looks like I'm gonna change out the filter caps and the rectifier this weekend so we'll see how it goes after that.

Murray

Yes they are nice radios. I have had three. All powered up and worked well when I first got them before I had even opened the back on the cabinet. I would recommend replacing all high value resistors especially those over 1 megohm. Also the electrostatic tweeter can sometimes give trouble in that it may have low output which was the case in all three of my radios. I haven't found a ready fix yet as the metal plate of the tweeter is rivited to the blue/green? plastic housing of the tweeter and I've found that removing it destroys the housing. Maybe you will be lucky and the tweeter will be ok. If all is ok with the FM band don't replace anything in the shielded area underneath where the 12DT8 tube is as that is the FM tuning circuitry with the tuning slugs. Component placement in that area is critical for proper FM operation. In fact don't remove the shield unless there is a problem in that circuit. I have one completely restored to proper operating condition that I don't use any more as I have no real use for only 1.5 watts output. I have two others that I had intended to fix and sell along with the restored one, but I havn't got around to it yet and probbably won't do it. How much did you pay for yours? I bought two of mine locally and one off the internet and paid $35.00 each.

Yes they are nice radios. I have had three. All powered up and worked well when I first got them before I had even opened the back on the cabinet. I would recommend replacing all high value resistors especially those over 1 megohm. Also the electrostatic tweeter can sometimes give trouble in that it may have low output which was the case in all three of my radios. I haven't found a ready fix yet as the metal plate of the tweeter is rivited to the blue/green? plastic housing of the tweeter and I've found that removing it destroys the housing. Maybe you will be lucky and the tweeter will be ok. If all is ok with the FM band don't replace anything in the shielded area underneath where the 12DT8 tube is as that is the FM tuning circuitry with the tuning slugs. Component placement in that area is critical for proper FM operation. In fact don't remove the shield unless there is a problem in that circuit. I have one completely restored to proper operating condition that I don't use any more as I have no real use for only 1.5 watts output. I have two others that I had intended to fix and sell along with the restored one, but I havn't got around to it yet and probbably won't do it. How much did you pay for yours? I bought two of mine locally and one off the internet and paid $35.00 each.

I got mine at the Thrift Store for about $20. I haven't done a thing to it and I'm trying to learn a thing or two before I even try. It works perfectly as is. I know there are resistors and probably some caps that I'll want to do at some point, but for now I'm really having a good time just listening to it.

I'm not sure if the tweeter is working or not. It sounds just fine. I may unhook the big speaker just to see if there is any sound.

Take care,

Ed

A good test would be to turn the tone control all the way clockwise and put your ear near the tweeter. Then see if you hear any sound from it. When on a good FM station if the tweter is working you will be able to hear it. Even on my radios I could hear the tweeter some. I'm not sure how loud it is supposed to be though.

... I may be incorrect, but I believe that the AC cord functions as the FM antenna, so if all you're getting is silence, you may have further issues.

The K731 does in fact use the line cord as an FM antenna. There is a small clip that is connected to the FM terminal; two inches of the cord (approximately) passes through the clip and is insulated from it by a small piece of cardboard. The clip couples the line cord capacitively to the FM antenna terminal and works well in most signal areas. If you need to replace the line cord, you can still use the new one as the FM antenna; just slip the new cord into the old clip after removing the latter from the old cord. This will not pose a shock hazard as long as the cord is in good shape, although I would line the inside of the clip with a piece of cardbord or other nonconductive material, just to be on the safe side. (I thank AK member old1625 for bringing this to my attention some time ago, in response to one of my posts regarding line cord replacement on my own K731.)

As to the silence Murray mentions, I agree. There could well be other problems under the chassis, or it may be as simple as a very weak tube. If you get reception on AM but not FM, I'd look at the 12DT8 converter/RF amp tube, as these often become "lazy" if the radio has been used mostly on AM and rarely on FM. I'd check the FM antenna connections as well. If the problem is vice-versa, I'd look for obvious things first such as missing antenna connections or a weak tube in the AM section; a weak AM converter tube can cause the local oscillator to quit at one end or the other of the broadcast band, or kill reception altogether if extremely weak (read so weak it might as well be dead, even if the filament lights--it is possible for a tube to light normally but not to conduct if it has low or no emission or open connections inside the tube, such as an open cathode).

As others have mentioned, the K731 is an excellent radio, one of Zenith's best table models next to the company's mighty 8-tube sets of the '50s-'60s. The '731 has a 5x7 main driver and a 3" electrostatic tweeter, so it will deliver excellent sound as well; these sets have very deep bass, again due to the 5x7 oval main driver (and an even larger speaker, 8 inches, in the C845 and others in Zenith's 800 series). The sound is excellent in other ranges of the audio spectrum as well.

Once you get your '731 singing again, you will be pleased with the sound. These radios represent a level of sound and build quality we will never see again; this is the main reason I like their older sets. I have several (K731, C845, MJ1035, R70, H480, et al.) and enjoy them all; as I said, once you get yours working as it should, I'm sure you'll enjoy it just as much.

Good luck.