Lytic Cap

[englissa]

question,, can you overheat a lytic cap when soldering it in to the point where the cap goes short ? thanks englissa

 

[Fisherdude]

That would be possible, but quite difficult to do. You would have to conduct so much heat to the interior of the cap that the dielectric insulation between the two films was destroyed. Were you soldering it to a pcb, or point-to-point wiring?

If point-to-point, the lead length would help keep the heat from damaging the cap. If you were soldering it to a pcb, the leads would be quite short, but if you were putting that much heat to the joint you would probably see heat damage to the pcb as well, such as lifted traces or visible discoloring of the board.

Was it a new cap? What makes you think it's shorted?

 

[englissa]

Fisherdude I rebuilt a can cap for a tube amp, there are four caps in this can, two 350 v something and two 50uf 50v. when I touch my meter probes to one of the 50v caps to ground i get a short but when I checked the outher one I get aroung 2 meg of resistance. All tubes are pulled so none of the interconnect wires between tubes are making ground. no I didnt check the caps beforing installing as they were new . englissa

 

[dshoaf]

Hope you wrapped that package of caps in insulating tape. Sounds like one of them certainly is touching the can.

How did you rebuild it, exactly?

Cheers,

David

 

[englissa]

here are a couple pics of it. I was careful when I assembled and soldered it in but I dont under why one side is going to ground. Yes i'm still learning englissa

 

[Face]

That's impressive.

 

[dshoaf]

OK, that is a nice setup. If it were my amp, I'd be pulling that cool-looking cover off and separating the 4 caps from each other first then test again to see if the short disappears.

You do good work, too.

Cheers,

David

 

[englissa]

the 4 axial caps glued together with all their neg ends ties together, gonna be kinda hard to seperate them . think i'll pull the yellow wire from the supscet termial.If ihe cap is bad then Ill take it apart unless somone has a better idea, I put a lot of time and effert into this PS i work in a machine shop. englissa

 

[englissa]

Ok just pulled the yellow wire from it and I get 0 ohms A SHORT.... What really maked me wonder is how a litic cap goes short. guess I take it apart :tears: englissa

 

[Fisherdude]

I'm guessing dshoaf is correct. You have something touching that isn't supposed to be touching. It appears that you have grounded the positive (non-ground) lead of that one cap.

 

[englissa]

I just clipped the neg lead from the common groung and measured the cap , DEAD SHORT. Unless something in the amp caused it of it was faulity from the factory, just my luck. First tube amp I work on and I get this. How many of you check your caps before installing them ??? well live and learn. englissa

 

[dshoaf]

Dude, I'm soooo glad you had the good sense to test and verify _before_ you powered it up.

Excellent job.

Cheers,

David

 

[englissa]

thing is I've listened to it for several hrs to it and it seemed to work just fine, I went back in to check the bias resistors and found a difference between the two when measured in circuit. thought one was bad so i removed it and after messing with it a while iI removed one outher and one thing led to anouther and brought me to the shorted cap. I was going to replace the bias resistor anyway with a slightly greater value. Oh its a AMPEX amp englissa