I'm brand new to this hobby.

I bought a Model L721, Chassis 7L05 Zenith AM/FM radio and am starting my very first restoration.

I've freed the chassis from the cabinet. Plugging it in I see 6 of 7 tubes lighting up and I'm getting static sounds.

1) Do I need to be afraid to touch the chassis? I assume you can't touch it while it's connected to the AC, but when I disconnect it? Does it still retain the power to shock me?

2) The tube that isn't glowing is the 6BJ6 R.F. tube. I assume this SHOULD be glowing so at the very least I have a blown out tube?

3) I know I need to replace capacitors, but before I get into that, how do I clean the chassis? Just blow the dust out? Is there any special fluid or spray cleaner or contact cleaner?

Thanks for your help.

1. Yes be very afraid. Never touch a hot AC/DC chassis. Use an isolation transformer. Unplugged, the set poses no danger.
2. Maybe not. Do not assume a tube that is not glowing does not work. Many tubes have low-level light. You need a tube tester.
3. I use a small 1/2 inch paint brush and a shop vac to get the dust off. Contact cleaner form Radio Shack or other works fine on variable cap and volume controls.
Careful and good luck. -Ken

Ditto to the above plus this: I would really suggest a simpler radio to learn on. The FM section will be more touchy about component placement and lead dress. I have two or three similiar Zenith chassis and they are not the easiest to work on for a beginner. But whatever you decide, please get an isolation transformer before you work on a hot chassis. Besides protecting you, it will protect any test equipment you connect to the chassis in servicing it. Since the tube filaments are connected in series on this chassis, it is quite likely that the 6BJ6 filament is lighting. If it were dead, all the filaments would be dead, and the radio would be totally dead. You would be getting no sound at all. Almost any component in the radio can be causing the trouble you describe. You need to learn at least basic troubleshooting and get basic test equipment before you will have any hope of fixing even the simplest of radios. Good luck and work safely..........GREG

Thanks for the fast response and the information. As you can tell, I'm a rank amateur.

I will look for an isolation transformer. I imagine this is something like those cut-off switches they have on bathroom and kitchen wall sockets--to cut the power in the event of a short?

An isolation transformer is different than that. Do a search of this site for isolation transformer and do some reading to get a good idea of whats needed. It an often debated/discussed subject here. But it is an important piece of safety equipment.

An isolation transformer is a good thing to have, but not essential. The important thing is to not get your body in series with dangerous voltages. You can still get a nasty shock, even if you have an isolation trans.

Cleaning (my method only):
1. Blow off all loose dust with compressed air. use a small paint brush to help loosen things.
2. Wash down with isopropyl alcohol---also using a paint brush, toothbrush, etc.
3. Compressed air again
After this, it depends on what things look like. For rust, naval jelly.

Pix:
I really think the use of compressed air can be harmful to your health in many cases. Some of that dust may contain all kinds of allergens and/or viruses. A vacuum cleaner plus a soft brush does just as good a job and removes the dust from your work area.

As to Populux's question, you would be wise to purchase one of many books on this popular subject. For a few bucks, you can find all you need for good, safe start in this hobby, and avoid some painful and dangerous situations.

Agree with all. If you can drag the chassis outside, wear a disposable mask and safety glasses, you can blast away decades of dust and whatever with air, whatever, let it dry for a week if you use a solvent.

Always fear touching anything when the set is plugged in.

Use common sense when working on electrical devices like radios. Don't work in bare feet or with shorts on: you can drop solder on yourself (I did!) Bare feet on a concrete floor are basically grounded so if you touch a live wire....in other words, wear rubber-soled shoes and stand on a rug or wood or a rubber mat if you're on concrete. When probing a live chassis keep one hand in your back pocket so you don't have an electrical path from one hand to another through your heart. Does all this sound scary? Radios aren't anything to be afraid of, but to be knowledgable about, and to respect.

This is an AC/DC radio with tube filaments wired in series. The 6BJ6 has a small filament so may not be noticed. It should still be lit.

The schematic can be found in 1953 Beitmans, page 188. Free here:

http://makearadio.com/beitmans/files/1953.djvu

With isopropyl alcohol, just a few minutes

Amen---just because you have things isolated, grounded, etc., does not mean you cannot accidentally touch something.

good point---I only use compressed air in an open space, and I avoid breathing the dust.

When I am more organized, I do start with the vacuum---and then the compressed air (it does get a few things that the vacuum does not---eg cleaning air-variable tuning caps)

Of course I'll get chastized from this but, since you are so uneducated about all this, and seem to know absolutely nothing past turning a screwdriver - I'd strongly suggests you pick up some books first, and gain some insight into what electronics is all about.

Side-stepping this most important tool and diving right in is not a smart way to get involved in a potentially dangerous "hobby".
You can't bake a delicious pie without having all the ingredients and utensils first.

Yet, as I read these threads - it continues - and always will - the ignoring of the proper pre-education certainly needed.
No, not everyone needs to take years of specialized classroom/field training and theory, tests, and shuck out money to an institution as I did to become a professional - but first things first - read a few books on the topic first.

And if anyone on here wants to hit me with crap to the contrary, they're just as wrong in doing so.

You either do things the right way, or bump along without the right tools and blindly make a mess of things.

No truer words spoken, educate before touching. What has taken years to learn some think its as easy as changing a light bulb.

I absolutely agree with Repair Tech!! Bravo!! Well said!!

To advise someone, particularly someone who doesn't know the difference between a dial light and a rectifier, that an isolation transformer is not an essential piece of safety equipment is nearly criminally negligent as far as I am concerned! Shame on the member who posted such a reckless comment...........

You can still receive a shock while using an isolation transformer, if you stick your person into an area it does not belong. But, an isolation transformer will protect you from the LINE. That may prevent you from being electrocuted if you should come in contact with something hot. And plugging the isolation transformer into a Ground Fault Circuit Interrupter (GFCI) is essential as well. Your entire shop should be so protected. And it is long past time that "newbies" be encouraged to receive at least basic troubleshooting training before they attempt to repair radios. Good luck and thanks, RT..............GREG

Repair Tech.......I have disagreed with you on different subjects in the past. I realize that my support in this thread makes no difference to you, but you hit this one out of the park!!

Here's some free literature to get you started http://antiqueradios.com/archive.shtml .

I've found "Elements of Radio Servicing" to be extremely helpful. Be safe and good luck.

I somewhat agree with needing to read books on the subject, but one can also learn by doing. I never really had any books when I was growing up. I just learned from experimenting and such.

Experimenting is fine if you have the months and years to learn. But to move things along in quicker fashion repair DVDs and books are out there which we didn't have in our learning days long gone by.

no fear. caution. know that there are high voltages. some sets have the line voltage tied one side to the chassis as a return circuit. it is dangerous. not something that you would want to play with barefoot standing on concrete floor. two handed is a no-no. your hands make a circuit across your chest. someone put the heart in there that doesnt like house current

Dear Sir-I wholeheartedly second "Elements of Radio Servicing". To me, working on radios is like riding a motorcycle. If you don't have respect (and a little caution) around these machines, then you should stay away from them. An Isolation transformer hooked up to a Variac (autotransformer), along with an inexpensive DMM or VOM, will go a LONG way in preventing accidents and assisting you in repairing your radio.
This is a fantastic forum, with a huge knowledge pool. Between that, your tools and yourself, you can repair a radio!:)
Still, I wholeheartedly concur about learning on a more basic radio, such as an AA5 AM radio, before attempting to repair an AM/FM. My dollars worth:)-Gearhead