Hi new guy here with a Zenith Automatic Frequency Control radio
 

Well I'm testing old radio waters and I bought a Zenith Automatic Frequency Control radio. I've been on this website for years and had no idea there was a forum devoted to antique radios, great stuff.

It's funny but when I took the plunge and bought this radio I thought it would probably be a transistor radio but it takes about 20 seconds or so for the radio to warm up so I'm guessing it's actually tubes.

The funny thing is I haven't opened it up yet to see what's inside. I'm a little stymied by its construction. It's a bit like a green plastic bucket that sits on its side. The face plate actually covers what would be the top of the bucket. I see two screws on the bottom and two screws in the back but I haven't figured out what these screws do or how to get inside.

I'm a little afraid to try and open it for fear of breaking or killing the thing. It plays reasonably well and tunes in my favorite classical music station quite nicely.

Can a radio such as this have a big improvement in sound by replacing tubes and capacitors or would I have to go so far as replacing the speaker? I realize it's not an audiophile piece of equipment but I like the old girl and was wondering if the sound could be tightened up a little. Below is a picture of this model of radio I have but it's not the exact one I have as my camera is traveling somewhere in Asia right now.

Thanks for any thoughts and advice you might have.

http://img23.imageshack.us/img23/450...icfrequenc.jpg

These Zeniths actually sound rather nice. Yours is indeed a tube type.

I second Hemingray's comments. Zenith made some excellent radios in their day, until they got out of the radio business in the early 1980s (1982, to be exact). I have three Zenith wood-cabinet sets (MJ1035, C845, K731) and a high-performance 13-transistor Zenith portable (R-70) that work well and have excellent sound, although as I write this the MJ1035 has a problem with the volume control--but when it works, it sounds great.

I'd leave the original tubes in your radio if the set works.

Replacing capacitors, especially the three-section electrolytic in the power supply (the latter is almost always bad in very old radios and is quite often on the verge of failure in 1950s-'60s receivers) in old sets is standard procedure when restoring them. Replacing the caps in and around the audio stages can improve the sound by altering the audio response curve. I would be careful not to put too large or small a capacitor in these circuits, the reason being that too small a cap will emphasize higher frequencies to the hilt and then some (the audio will sound abnormally shrill); too large a cap will overemphasize the lows, resulting in an excessively bassy sound.

If you have the room in the cabinet and can find a larger speaker, by all means go ahead and replace it--you have nothing to lose and everything to gain in terms of improved sound quality. Note that you can always replace a four-ohm speaker (for example) with an eight-ohm one with no fear of damaging the radio's output stage (the only thing you will lose is a little volume), but not vice-versa. Replacing an eight-ohm speaker with a 4-ohm one or less will damage the output transformer and/or other parts of the radio. The best thing is to replace the original speaker with one of the same impedance; the use of higher-impedance speakers is an emergency procedure, to be used when or if the proper speaker is unavailable.

Good luck. I'm not really all that familiar with your particular Zenith radio, but the company's sets from the '40s through the '60s were excellent radios, with no production shortcuts. You won't be disappointed once you get your set working. These radios, as I have mentioned many times in this forum, represent a level of sound/build quality which we will never see again, in this age of cheap plastic one-chip headphone stereos. Once you get that set singing again, hold on to it. As I have also said (and believe with all my heart, as I am a Zenith radio collector and have a great deal of respect for the original Zenith Radio Corporation of Chicago), they don't make them like that anymore.

I'm not too certain, but if it's like my white Zenith radio (which has this same dial and knob layout), it probably uses a 6BJ6 for an RF amplifier. These guys can pick up FM real good. great with AM too.

I've got one of those sets buried here somewhere in need of restoration. If that radio uses a selenium rectifier (fin looking device), it should be replaced with a modern silicon diode (something like a 1N4007) and a voltage dropping resistor. The electrolytic and paper capacitors should be changed. By the time this radio was made, many paper caps were being made with so called sealed plastic housings. I find that these are just as prone to leakage as their '30's wax covered family members.

Lastly, there is one thing that you should be aware of. This radio likely has a "hot" chassis. What that means is that one side of the AC line is directly connected to one side of the chassis. This poses a serious shock or electrocution hazard. The safest way to work on one of these is to use an isolation transformer. If one is not available, use extreme caution and don't allow any part of your body to touch anything that might have a path to ground while working on the chassis. Try not to even touch the chassis while it's powered up if an isolation transformer is not used.

Most transformerless sets that you find will either have one side of the AC line connected directly to the chassis or have one side of the AC line connected to the chassis thru a capacitor. Zenith seemed to love the direct approach. Many of their tube radios had a printed warning on the back cover stating that one side of the AC line is directly connected to the chassis. This goes for tube and early solid state models.

http://antiqueradio.org/welcome.htm

Click on the link for beginners. This is a very good, informative website for those who want to learn about old radios. Be forewarned, once you start, casual interest quickly becomes avid hobby :yes:

That bug already bit me back in high school. :thmbsp:

Damthaings TALK to you...You'll see one, sittin' forlornly in an antique/junque/shoppe somewhere, & it'll look at you sad, & say- "Take me home w/you, Mister, please ? I'm just a nice li'l ol' All-American Five, I'd be a GOOD radio, always give you Good News...Whaddya say, pal ? Come on, you KNOW you want me, I'm kinda cute, & with a wipedown w/a damp, warm rag, I'll look like I was new again...Come on, pal, let me come home with, OK ?..." And dammittall, I'll end up bringin' ANOTHER one home...(grin)

You summed it up perfectly Sandy! They do seem to have consciousness.

John

I have several of these in different styles with the same chassis. One of the best table FM radio's of the day. All of mine played great from the start but a recap did improve the sound quality on a couple of them. Nice Find!
-Tony

I have that same problem! Even if it is just some dinky AA5 radio. :thmbsp:

Well, misery loves company, I guess...Good to see I'm not the ONLY one that thease damthaings "talk" to...(grin) But wait til you run acrost a Grundig, SABA, Emud, or Nordemende...They ORDER you to take 'em home !!

LoL!!!! My Grundig ordered me to bring it home, now it orders me to listen to it once in a while. Nice Zenith BTW, you will have many good years of listening from that one. Also, get any of those white porcelain caps out too, (if it has them) they like to explode sometimes. Usually when rap noise comes on.:D

Nice score on the Zenith radio. I had a K731 that I bought brand new when I was a teen in the 60's. I'll send a pic later. My aunt and uncle had one of those C845 or H845 like Jeffhs. These baby's could pull in the stations with just the cord antenna! I remember listening to my aunt and uncles while baby sitting for my cousins and pulling in stations from Chicago from Grand Rapids MI (thats about 100+ miles away) with just that cord antenna. They don't make um like they use too!

Here is the pic of my Zenith K731

I also agree with updating components. It would be a shame to loose a good old radio because of component failure. When I went through my H845. I replaced the selenium diode with a silicon diode. I also replaced the electolytic and wax caps. Cleaned all the pots and replaced all the tubes. All my tubes were original and were weak. The thing is great. It sounds better than my Pioneer SX-780. It is on my work bench up at the plant and I get all kinds of compliments on it. I have only gotten a couple gigs about being an I&E tech with a tube radio. Oh well.

Thanks lads for the great info and advice.

I still haven't gotten around to cracking the Zenith open yet but I've been playing it a few times now and it sounds pretty good. I'm sure it could sound better though.

One of these days I'll pop him open and hopefully take some pictures in the process. :music:

If you ever run acrost a Zenith MJ-1035, GRAB IT !! That's an order... (grin)..Seriously, its their TOTL table set from c. 1965, has 11-12 tubes, & should have an outboard speaker for stereo w/it. They sound great, & are pretty good at picking up distant stations, both AM & FM...You WON'T be sorry if you get one !

I'm feeling much better actually.

Well I finally opened up the Zenith. I was going to make a list of the tubes and see if there were any leaking caps and such. I got the chassis out of the plastic bucket with no trouble. I counted 7 tubes 3 of which were zenith which looked quite old and 4 of which were Sylvania which are rather new. Kind of a bummer because the markings stating the type of tube are quite faint and unreadable. Hmmm.

I tried to get the bottom plate off to scope out the capacitors but the way the thing is setup I can't get my driver on the last two bolts. Hmmm.

Well I was then checking out the speaker when I noticed something jammed in between the basket and the cone. It was an 8" long, 1/2" inch wide strip of black velvet. They use it all around the face plate to make a nice seal when it's all closed up. Apparently when the last person was in the radio they pushed the face plate on and the velvet wound up jammed against the back of the cone. This was clearly causing some of my bad sound problem.

I freed the velvet and glued it to the top of the faceplate where it belongs. I bundled it all up and gave him another try. Wow! What a difference. It's funny because before the tone control had almost no effect at all. Now the sound is much more open and I can flatten it out or lower it with the tone control. Very happy!

This is one nice radio after all. Some day I'll figure out what tubes are in this thing and replace them all as well as the caps, for now it sure does sound nice.

Thanks for all the advice lads. I'll be back with this radio one day with some more questions. :music:

Sounds like a C725 that I have. Does it look like this one?

http://www.audiophool.cjb.net/zen_C725C.jpg

That's it exactly dude except that the plastic bucket part on mine is a pale green. How do you feel about the sound that your Zenith produces Tom?

He's not a bad radio and if you let it warm up long enough he sounds pretty nice. I've been using him as an early morning radio and light night working radio.

I was going to spring for an old sony table top radio but since I freed up the speaker I'm happy with this guy for the time being with his tubes. :music:

Hey Chasaboo, The sound is great from my Zenith. It is a two way system. There is like a small tweeter on the left hand side. Sounds pretty good.

Wow, I can't recall seeing a tweeter. I'll have to open him up again and see.

I'm pretty sure all I had was the one oval speaker.

It sounds pretty good since I straightened it out.

yea there is an oval speaker and a small little tweeter on right side( not the left as previously stated). It adds some highs when you turn up the treble.

Repeating what others have said.....these 7 and 8 tube Zenith's with AFC produced from 1955-67 were so nice. What make them enjoyable is, they were a medium sized unit at about 15 inches wide & about 10 lbs. but they performed like a bigger radio. Zenith quality was A1 !

They stop me in my tracks when ever I see one at a radio swap, flea market or yard sale...if priced right, I end up bringing it home. The collection is starting to get out of hand - the family includes..Y832, H835, C835, C845, H845,C730,C735, K731 and about 20 of the smaller Zenith's from the 50s & 60s. Recently I've become interested in the top shelf solid state AM/FM models from 1968-71 with the acoustic suspension loudspeaker & wood cabinets. Yes, they are transistorized, but are very nice radio's with impressive audio, and as it turns out, were among the last of the Chicago made Zeniths ! (these can be found for very low prices still....$5., $10.)

Time to get another bookshelf for all these !

I live in northeastern Ohio near Lake Erie and close to Cleveland, Erie, Pennsylvania and Youngstown, Ohio. When the conditions are right, I can receive stations on my C845 from Erie and Youngstown (and Cleveland, of course), simply using the line cord as an antenna, just as well as if they were local. Being so close to the lake (within one mile), I often hear stations from southwestern Ontario, Canada on my C845 in the summer as well. I bet it's the 6BJ6 RF stage and the two-stage (three if you count the limiter stage--this radio does not use the standard FM ratio detector) IF strip that does it. Zenith's engineers obviously designed the C845 and its variants for DX reception and great sound. I bet a lot of these radios were sold in weak-signal areas.

I have a K731 as well that is every bit as sensitive as my C845. In addition to the FM RF stage, this radio also uses, like the '845, a limiter stage ahead of the second IF amp, which amounts to three IF stages. The sound is pleasing and better than most table radios of that era (early 1960s), but not as good as the C845, due to a 5x7 oval speaker and an electrostatic tweeter driven directly from the plate of the audio output tube (35C5). I think my K731 is a little too bassy, even with the tone control set close to midrange. With the control set fully CCW (counterclockwise), the bass is so strong that I'm actually afraid the speaker may be damaged. On the other hand, the tone control on my C845 does not overemphasize the bass range, even with the control set fully CCW. (I usually set it at midrange and leave it there.) I'd be interested to know why there is (or should be) such a difference in tone control action between these radios. The only thing I can come up with right now is that one or more caps in the tone compensation circuits of the K731 may be leaky or may have drifted in value (if such is possible with capacitors as it is with resistors). Haven't recapped either set yet.

I still haven't replaced any parts on this Zenith and it really does sound magical. The music from it is just stunning. I mostly listen to classical music and some blues.

I'd be nervous to replace anything for fear of ruining the good sound it does have. I'm keeping an eye out for another one in case this one does blow up.

Thanks for all the great advice and info you've given me in this thread. Really great stuff.

Zenith, the quality goes in before the name goes on. :thmbsp: