Zenith Tube Radio

hbucker

hbucker

Well-Known Member
I just inherited my Dad's old Zenith tube radio. It is in excellent condition and works, but I'm sure the tubes are the original tubes. It is a mono radio and there are SEVEN tubes inside. (This amount of tubes really surprised me.)

Questions:

1. If it is working anyway, could I expect to improve its performance by replacing the old tubes with new ones? I'm not looking for super high fidelity - simply wanting it to be at its best.

3. If tubes are replaced, is there any biasing that would need to be done?

2. Is there a place you can recommend that sells replacement tube kits for specific radios?

Thanks
 
hbucker said:
I just inherited my Dad's old Zenith tube radio. It is in excellent condition and works, but I'm sure the tubes are the original tubes. It is a mono radio and there are SEVEN tubes inside. (This amount of tubes really surprised me.)

Questions:

1. If it is working anyway, could I expect to improve its performance by replacing the old tubes with new ones? I'm not looking for super high fidelity - simply wanting it to be at its best.

3. If tubes are replaced, is there any biasing that would need to be done?

2. Is there a place you can recommend that sells replacement tube kits for specific radios?

Thanks
Click to expand...

Thread Is Worthless Without Pics.


1. If it is working anyway, could I expect to improve its performance by replacing the old tubes with new ones? I'm not looking for super high fidelity - simply wanting it to be at its best.

--No, if the tubes are good, leave them alone. Those older tubes are actually much higher quality than those that are built later but it might not hurt to find someone that can check the tubes. However, what DOES need to be done is someone to go through it and replace wax and/or failing capacitors.


Actually that pretty much answers all three questions.
 
Exactly what he said. Don't go wholesale swapping of the tubes. First, the Zeniths (depending on the year) suffer from brittle wire disease. Look it over real good and make sure that none of the wiring under the chassis has lost its insulation. Secondly, get a parts list and schematic for capacitor replacement. (Several free places on line or email me and I will send you the file) At a bare minimum, the electrolytic caps need to be replaced. (If they had not be replaced recently) It may play but if the electrolytics have not been replaced you'll end up doing more harm than good at some point. And lastly, again as stated, replace the old wax caps.
 
Indeed, fresh capacitors in the right places will insure proper operation.
But hardly mentioned are the aged resistors - they tend to go out of tolerance too.
And certain Zeniths using selenium rectifiers could benefit from a new diode in there.
Also in certain models, the feedback lines really need re-designing because of their overly-emphasized bass properties. - in the "old days" radio stations didn't boost the bass like today, and so that "emphasizing" in the radio isn't needed now.
 
If it has an old 6X5 rectifier tube, you might want to replace that with a 6X5GT tube or silicon rectifier circuit. Many classic Zeniths that used the 6X5 suffered from catastrophic power supply transformer failure due to internal 6X5 shorts.
 
specialone53 said:
....But hardly mentioned are the aged resistors - they tend to go out of tolerance too.
And certain Zeniths using selenium rectifiers could benefit from a new diode in there.
.....
Click to expand...

I agree 100%, lots of people do not realize how much those old carbon comps have drifted upwards.

And I'm really not too fond of keeping those old seleniums in there either, even when they were new they weren't all that reliable.
 
If its what I'm thinking it is, its an AM-FM set that Zenith made by the GAZILLIONS from the late Forties thru the mid-60s.There were a myriad of models & cabinet styles. They were good, solid performers. Go thru it & do a little PM as described, & it'll likely give ANOTHER fifty-odd years of service !
 
Only one picture came through. It's statement that "the chassis of this receiver is connected directly to one side of the line" clearly means to me that this is a hot chassis radio. If it's an AM only set, it's an All American Five (named that way because they're hot chassis, 5 tube sets). Tubes will be something like a 50C5, 35W4, maybe a 12AV6 or so.
 
Hmmm.... All 3 came through for me and are from the same source. Try a refresh?

It is model: S-42505

am/fm radio

thx
 
Yep, about what I thought. I have its "Double-First Cousin", blonde wood cabinet & all. Mine has gold/maroon knobs & the whole front is slightly different in detail. Its late Fifties/early Sixties. Give it a GOOD outside antenna, a little maint on the tired caps & resistors, it'll make you smile. Tubes AREN'T nearly as fragile/prone to failure as most people think.
 
No useful info on the bottom as far as I can see. A partial schematic, but it has mostly fallen off.

Late 50's or early 60's is when my Dad would have bought it.

Thanks guys. :thmbsp:
 
It wasn't really a schematic, but a tube chart showing where the tubes went. That's where the model number and chassis numbers would be shown.

You may be able to see a chassis number printed on the chassis itself when you take the back cover off (don't do that with it plugged in!) If you don't see a chassis number, get the numbers off the tubes and compare that to the models similar to the one I posted from radiomuseum.org.
 
I have a plastic cased version of this radio, they were from the mid 1950s-mid 1960s they have 7 tubes in them (so its not an AA5 radio) but it is a hot chassis but the way they made these is that they have a interlock plug system so that when you service the radio you don't have any sort of connection to the powerline when you are servicing it which then prevents the deadly electric shock that you tended to get from servicing these old hot chassis radios.
The interlock plug is more or less a safety feature that Zenith came up with so that servicing these radios wasn't as deadly as it was before.

These old Zenith's have uber sensitive tuners so they can really pick up lots of stations even with just the built in antenna.

Enjoy the radio.
 
These am/fm Zeniths are great performers. They even use 2 IF stages on the AM band. Some vintages of these can suffer from silver mica dissease, corrosion of caps inside the IF cans. Hot chassis, so use these with a isolation trans or a GFI.
 
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