Identify a part? - Videokarma.org TV - Video

tgunner · #1 03-02-2008, 09:12 PM

Who can tell me what this is? It is connecting a terminal of a Selenium Rectifier to the body.

radiotvnut · #2 03-02-2008, 09:16 PM

That's the death cap! Get rid of it now! This is a "bumblebee" capacitor. If I'm reading the color code correctly, you can replace it with a .047 uF, 600 volt cap. This cap is connected from the hot side of the line to ground and these are bad about shorting and exploding. Like I said, change it NOW!

radiotvnut · #3 03-02-2008, 09:41 PM

Some other thoughts: I can see that's a Zenith chassis. Those sets have one side of the AC line connected directly to the metal chassis. When the set is plugged in, there is a 50/50 chance that the hot side of the line is connected to the chassis. If you touch the chassis while another part of your body has a path to ground, you will receive an electric shock, possibly lethal! It's best to plug these type sets into an isolation transformer for service. This will greatly reduce the shock hazard while working on these sets.

You'll also be better off replacing that selenium rectifier with a modern silicon rectifier. Something like a 1N4007 should work fine. You'll need to place a resistor ahead of the new diode (between the AC input and the anode end of the diode). A 68 ohm, 5 watt resistor should work. The reason for the resistor is because there is less voltage drop across a silicon diode than there is across the selenium. Those old selenium's would short and give off a foul odor. I've also seen them become weak and the B+ voltage would be low.

tgunner · #4 03-02-2008, 09:56 PM

Thanks for the help. For now I am just concerned with replacing the main power supply cap, and the "bumblebee" as it's shell is cracked. The radio does turn on, but has the common tube hum. Any ideas on where to source a new power supply cap? It is a silver can, 40, and 80 uF at 150v each.

radiotvnut · #5 03-02-2008, 10:17 PM

You'll probably have to use individual sections as the metal cans are hard to find (and often expensive) these days. www.tubesandmore.com or www.justradios.com sells the individual capacitors you need. Just make sure to disconnect the old can and you'll probably have to install a terminal strip somewhere under the chassis to mount the new capacitors.

tgunner · #6 03-02-2008, 10:34 PM

I was looking at this http://www.tedss.com/2020000764/ but the site requires a $25 minimum order.

kcollins4 · #7 03-02-2008, 10:39 PM

It would seem after radiotvnut's post that a first order of business would be to change the cord cap to a polarized one installed correctly.

Then tackle the problems.

tgunner · #8 03-02-2008, 10:49 PM

I'm not too worried about the plug and power; when the radio is apart the plug disconnects from the chassis along with the rear cover.

radiotvnut · #9 03-02-2008, 11:09 PM

I can't believe I forgot to mention it; but, I do replace the line cord on most AC/DC (transformerless) receivers with a polarized AC cord. Some older models did not have any type of isolation for the control shafts or chassis mounting screws. Even with a polarized plug, there is still the chance the radio will be plugged into a receptical that is wired wrong.

easyrider8 · #10 03-02-2008, 11:18 PM

The selenium should be OK with new filter caps. Mount the new filters under the chassis and disconnect all the wires from the old can. You should use a line cap to replace the bumblebee, you can get them from Dave at justradios.com, they will be rated X,Y. Actually all the paper caps should be replaced.

Dave

drknstrmyknight · #11 03-03-2008, 01:01 AM

"Those old selenium's would short and give off a foul odor."

A foul toxic odor...

Check this out for yuks
http://antiqueradio.org/tvshow.htm

mr_fixer · #12 03-03-2008, 02:54 AM

Thats so funny, Death by Old Radio! dah dah dah duh! It would be our luck if some politicians, who saw this movie decided to pass a law banning old radios, to prevent a one in a hypergazillion chance of this ever happening. Especially considering that just eating a spoonful of Dandriff shampoo would have more selenium than a rectifier!

tgunner · #13 03-15-2008, 03:44 PM

I bought a Sprague Orange Drop to replace the Bumblebee. Can someone help me with the polarities?

Fisherdude · #14 03-15-2008, 05:35 PM

The bumblebee and the orange drop are not polarized caps. Any way will do.

Btw, when I read through this thread, I wondered how you determined that the can-style cap was bad. You mentioned that the bumblebee was cracked. You might find that the hum is gone when it's replaced.

Boobtubeman · #15 03-16-2008, 02:40 PM

As far as the main can cap goes, theres a guy at dialcover.com that sells re-stuffed caps for zeniths.

I got my dial string and a manual for an h-500 radio..

Steve