Zenith Tube Radio
- Thread starter hbucker
- Start date
KutzlerTrans
Jennie & I with Buddy and Barney.
Thats a New one. I was thinking big upright with shortwave. Its funny how i've been away from tube radios for 40 years and still remember 35w4's and 50c5's.
Zenith is quality stuff. Good for you!
You did the right thing by asking first before plugging it in. The help and advice you are getting here is the best:thmbsp:
Inspect that cord for dry rot and blow the bugs out of it. Have fun
Zenith is quality stuff. Good for you!
You did the right thing by asking first before plugging it in. The help and advice you are getting here is the best:thmbsp:
Inspect that cord for dry rot and blow the bugs out of it. Have fun
pete1729
Super Member
This looks like a 700 series. I rebuilt a Zenith 835, I resuffed the power supply can capacitor and replaced all the electrolytics. I replaced the tweeter with a modern Vifa from a organ donor speaker. It took two evenings and very little swearing.
My grill cloth was not nearly as nice as yours, so I replaced it. It's a daily driver and resides in my kitchen. It's eminently satisfying to listen to, I imagine yours would be much the same New Orleans has good radio.
My grill cloth was not nearly as nice as yours, so I replaced it. It's a daily driver and resides in my kitchen. It's eminently satisfying to listen to, I imagine yours would be much the same New Orleans has good radio.
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Trio
Super Member
New tubes does not equal performance.
The simplest strategy is to replace the filter caps first, there may be an electrolytic in the final audio stage- replace that too. Then turn it on. If it works, you can adjust the trimmers on the tuning gang for peak signal with the antenn you are going to use, there is an oscillator trimmer which will affect where the needle is indicating on the gang as well- you will know right away once you move it.
If it tracks okay, so that 700 lines up with 700 and 1500 lines up with 1500 (or stations in the vicinity of those) You are good to go.
You can peak the IF's for maximum signal and sensitivity, but you might alter tracking on the dial. Most likely you will get the stations I mentioned as marking points, but they might land on 750 and 1400. adjusting for slightly less peak will broaden that out, but it also does so at the expense of sensitivity.
If it does not work after the filter caps have been replaced, you should check the tubes for merit. One bad tube will cause it to fail to function. If the tubes are good, then you need to look for resistor issues- Check each tube's plate voltage (as long as it has octals, locktals or conventional mini 7 and 9 pin tubes. Larger 4, 5, 6, and 7 pin tubes must be kept vertical when in operation (for simplicity) otherwise the filaments can short to the grids or plates. If all plates have some measurable voltage, then either jumper each paper cap with a good condition paper cap until you find the one that is bad (open usually) and replace it, or just recap it entirely for reliability.
That is it in a nutshell. I have done so many of these I can do them in my sleep.
If you'd take the back off and snap a pic of the innards, the guys would be able to help a little more. In my experience, the chassis number is ink stamped on top of the chassis. Like 7K07. The same chassis would be in several different radio model numbers like K731. Seven tubes.
Murray
Murray
hbucker
Well-Known Member
The thing is, it works. It sounds like an old radio, but it works. Was wondering about simple ways of improving it, but a complete overhaul just to make it sound a little better is a bit more than I was thinking of at this point.
I'm use to tube guitar amps and have no real experience with these radios - although I grew up with this one. I just don't have any experience with the innards. I was shocked to see so many tubes: 7. And was even more surprised to see so many different kinds (as apposed to 2 different kinds in a guitar amp.
I appreciate all of the input and will reference this thread if anything goes wrong with it. You guys are a great resource.
I'm use to tube guitar amps and have no real experience with these radios - although I grew up with this one. I just don't have any experience with the innards. I was shocked to see so many tubes: 7. And was even more surprised to see so many different kinds (as apposed to 2 different kinds in a guitar amp.
I appreciate all of the input and will reference this thread if anything goes wrong with it. You guys are a great resource.
nashvillebill
Super Member
Thing is, if you don't do a little preventive maintenance at this point, it may soon stop working. It's a 55 year old radio using capacitors that were lucky to last 20 years! Replace the electrolytic capacitors at least, they're living on borrowed time.
If you don't do a little preventive maintenance now, repairing the radio could be even more work in the future.
A PM rebuild will probably make it sound better. Zenith AM/FM tabletops are usually pretty good performers when working correctly. I've worked on models with the same or a very similar chassis before, and they sound quite decent when they're right. Not a lot of parts in there either. From memory, its maybe a dozen paper caps, the 3 section electrolytic and a selenium rectifier. Its an easy afternoon rebuild.
Just did this on mine. 7K07 chassis. New filter caps and selenium replaced with 1N4007. 22 ohm power supply resistor changed to 47.
+1:thmbsp:
Also replace the tubular capacitors not plastic film types.
Otherwise it is what it is as-is, best left as-is after refurb.
Don't freak out about the tube count, my Packard Bell 1960's stereo with FM/AM stereo radio has 13. My decommissioned (put in storage) Magnavox 25 inch color TV has 23.
Do what they are telling you about replacing weak parts. They are right, it's not about sound quality. It's about making the radio safe and lasting for years to come. If truly care about this radio, do what they are telling you.
I made the mistake of doing a partial rebuild one of these, and it cost me an irreplaceable IF can. If you are uncomfortable with rebuilding, find someone that can do it.
FM/FM Stereo tube radios are not something for a novice, it's very easy to screw something up, and almost impossible to get it back without the proper equipment.
If you want to learn, get a junker radio and practice on that before working on this one.
drknstrmyknight
Addicted Member
It's AM/FM (see picture).
Has the internally riveted line disconnect rather than the rubber through the back type, so maybe a c730 chassis, or so c 1960
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Trio
Super Member
Replace the filter caps (safety issue), and the other electrolytics (also safety issue)- since it works, you can leave the paper caps in it untouched. Zennith did have tight quality control and those caps might hold up another 50 to 60 years or more. The filter caps will not though.
If you peak the trimmers on the tuning gang, this will match the radio to the antenna for peak performance. You will be amazed at how many more stations you can pull in with this radio than with your stereo.
Gadget's suggestion applies especially if the magnet has lost it's magnetic field, which can happen, and is also one of the things people will do if they have an electrodynamic speaker with a burned out field coil.
With parience and without a great deal of effort, nor equipment- you can peak the AM IF's- these should be stamped on the side- 455K, 455KC or 455KCy. But you should understand what the purpose of the alignment is and what they do so you can use the radio stations themselves and the tuning dial to do it correctly.
The FM IF's should be left alone if you are getting all the FM stations in at the correct location on the dial- if it happens they are all evenly off- just tweek the FM oscillator trimmer on the tuning gang to bring them into position. If they are all in the correct spots, the IF's are fine.
specialone53
Active Member
I can tell you're not familier with this particular radio chassis.
It's got a standard PM speaker.
It probably has some black beauties in it that should be replaced right away.
FM is slug tuned, and should not be messed with by tinkerers.
