new to tubes

[boyesreef]

hi, im nick. im new to tube technology but find it fascinating. i was given a broken radio to fiddle with and managed to get it fired up. heres pictures of it.









i know nothing about it other than its a zenith am/fm table radio with clock and alarm. if you have any other info let me know. i cant find it online anywhere. it dosnt seem to get any stations real well, am or fm.

[Sandy G]

Looks to be a mid-late Fifties Zenith.... They made a blue JILLION of these, in a dizzying array of cabinet styles.. How many tubes ?

I think that is a model J733 from 1952. I has 7 tubes. I didn't see a schematic for it on www.nostalgiaair.org (which is usually a good source for free radio schematics), but there are some for sale on ebay.

[boyesreef]

one differance i notice is mine does not have the third nob at the 12o'clock on the dial.

[Geist]

Hi;
What did you do to get it going ?? Have You replaced any of the Caps ?? I wouldn't leave it plugged in for very long, until you do..
THANK YOU Marty

[boyesreef]

well when i got it it would run the clock but that is it. actually all i had to do was plug one of the tubes back in. it had creeped out fat enough that a couple poles werent touching. had a problem yesterday though. ive used the radio for a few hours before this point, but yesterday about an hour and a half into listening i got an audible pop and a wall of blue smoke from the back of the radio. but the radio continued to play. of course i unplugged it right away, and this is what i found.







any ideas on the value of this unit, and what it is (resistor is what i think)

it was connected between the blue box and the chassis.

[old_tv_nut]

It's a capacitor ("cap") and this is why they should be replaced.

[dtvmcdonald]

Its a 0.047 microfarad paper capacitor. Replace with a like value
600 volt mylar. It may be directly across the AC line, so you
need a really high quality one.

These striped caps are known as "bumblebees" and they really
tend to behave like that one.

By the way, that blue thing is a selenium rectifier. If the radio
starts to stink very very bad, it's the cause. Bad ones cause the
selenium to react with its paint and make hydrogen selenide gas,
with is roughly 10 times time as poisonous as hydrogen cyanide.

If that happens, take it out doors immediately.

Doug McDonald

[Jerryhawthorne]

Nice to have new people in the hobby. Listen to the advise. Nice radio but you have some parts in there that are ready to give up the ghost. You just found one! As said, that cap is probably across the A/C line and with age, when they give up, short out and tend to explode! There are a few other caps in there that should be replaced as well. As this is a newer radio (so to speak) you will have to find someone who can link you to a schematic from "SAMS" that published schematics for post WW2 radios. Going through and replacing any of those nice bumblebee caps and the couple of electrolytic caps should get that radio back and singing nicely and safely.
Enjoy the hobby, it's a lot of fun. I should add that this radio is an AC/DC radio. That means there is no power transformer in it to isolate you and your body from some nasty shocks. Do NOT do any work on the radio, touching the chassis if it is plugged into the wall, even if you have the on/off switch turned off. Always unplug the radio when touching the bare chassis.
Jerry

[DavGoodlin]

The cap across the 120 volt line should be X2 or Y2 rated .047 thru .1 microfarad.
I get mine from old CRT monitors and other modern electronic junk.

[zeno]

Very nice starter radio. Look in the library for an older
radio repair book, most 50's radios are the same design so
it will help you along. Most use the same 5 tubes & are
called "all American fives". Yours is FM so it has a few more.
Other essentials IMHO are:
Isolation transformer preferably with built in variac such as
a Sencore "power right"
A GOOD digital meter such as a fluke, beckman etc.
A good soldering iron & soldering gun.
If you get into it there are some other things that
are nice but not essential.
When you are done you will have a radio that is better than
any of the pure junk made today. It will easily live 100 years
more with just minor repairs.

73 Zeno

[Tubejunke]

I would look for a decent tube tester if I were just getting into thermionic emission. You don't need anything fancy with mutual conductance capabilities; just basic emission, shorts, and gas tests will do.