Zenith K731

[Fast_Eddie]

Originally Posted by Fisherdude

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.

[skippy_ps]

Originally Posted by Fisherdude

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

[Tube Radio]

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.

[Fast_Eddie]

Originally Posted by Tube Radio

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

[Tube Radio]

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.

[Jeffhs]

Originally Posted by Fisherdude

... 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.