Several reports of Black Gates failing

[fdegrove]

Hi,

OK, Frank but you have to agree with me that using components above their maximum ratings never is a wise thing to do.

Of course I agree.
I always design with a safety margin of at least 30 to 40% when it comes to caps.

If anyone would take a look at the Caesar circuit they could have predicted it easily.

Measured voltage is already a high 85 VDC,add to that the modulated AC signal voltage and you know that 100V insulation is not enough.

Any other cap would behave as described in above post.

One of the major problems with designer software is that it usually doesn't take dynamic conditions into account.

Cheers,

[jeff mai]

Originally posted by fdegrove
So while these caps explode they open the circuit,at worst they take the cathode resistor out as well.
That's the only damage you'll have..

To the amp maybe. You could lose an eye if it happened while you were prototyping an amp without a chassis.

The BGs however conduct fully since they short the plates internally...this shorts the cathode out and the tube will go into thermal runaway...till it dies.

You could prevent this with a fuse in the cathode circuit.

BTW, the Nichicon cap failure I mentioned above was a short, not an explosion. It isn't only BG caps that fail this way!

[fdegrove]

Hi,

It isn't only BG caps that fail this way!

No?

In that case I'd like to know the guilty ones.

I insist on this because it is :

A) an expensive adventure.

B)a freaking mess

C)safety??

Sorry to act like this but caps behaving in such an unexpected way can set fire to many an household.

Better safe then sorry,no?

Cheers,

[jean-paul]

Frank, I respect your knowhow a lot but please think before you start the witch trial on BG ( which you have never even used before as you said in another thread ).

What do other caps do in the same situation ? I told you some of my experience and you seem to think only BG fails this way.
Caps sometimes short or open when failure happens and sometimes they even explode in the most extreme cases. A fact despite their safety vents and all the engineering that's behind the product to prevent it from doing so. At school we did the experiment with Philips caps. They blew as well.

So:

A) an expensive adventure is always a possiblity. Could be a cheap Nichicon that causes your expensive 300B to blow.

B) a freaking mess always occurs with this kind of failure. With BG, Elna, BCComponents or whatever brand / type.

C) For safety testing one Ceasar owner should try another brand and see what happens. I advise him or her to wear safety goggles with this experiment

These things happen. For instance I have a defective Pioneer DV-K101 here that has a IR3M03A 8-pin switching regulator used well below specs for creating a negative voltage from + 12 V. Current is no higher than 100 mA. Nevertheless this IC was probably made on a monday because it managed to burn the PCB and took the DAC with it... You know that a real 230 V switch costs too much nowadays for most manefacturers of equipment. So it failed and power was still on. Could have been my household that burned. Still I don't think all these regulators exhibit the same behaviour. Mine did.

[fdegrove]

Hi,

Sorry if it seemed that way...no I don't want to haunt the BG in any way.

Still,I find it worriesome to see them behave like that and for safety's sake I only want to find out other manufacturer's product behaving the same way.

No more,no less.

Pls,read what I posted before and you will understand my concern.

Cheers,

[jean-paul]

Hi Frank,

There is a possibility that the graphite particles in the BG's will conduct in case of using them over their maximum ratings.
I don't know. I reread tour posts and understand your concern very good. Maybe one user with such a shorted cap could send a mail to Jelmax Japan for more information on the matter of the shorting of the cap. I am still convinced that other types behave the same but maybe in a lesser degree. Reason for some concern as you stated correctly.

In the case that BG is "oversensitive" to exreme overvoltage one should always choose a cap with a very large margin, say 50 or even 100 % above the voltage that it normally sees. Is always wise to do. Comes to my mind a magazine once advised to choose the electrolytics max. voltage rating close to the actual voltage in that application. They probably didn't test BG that time.
Just think what Silmic ( with silk and hemp) or Cerafine ( with ceramics ) or OSCON ( "organic" stuff in it ) will do when exposed to extreme voltages ?!?!?
The smoke of the hemp in the Silmic's won't hurt for sure.

[fdegrove]

Hi,

In the case that BG is "oversensitive" to exreme overvoltage one should always choose a cap with a very large margin, say 50 or even 100 % above the voltage that it normally sees.

Nah,I don't think the BG is at fault.

I know Dick made a mistake though.

Since he is such a formidable chap I tend to forgive him...

Surely you don't mind anyone trying to find out other manufacturers' caps behaviour under fault conditions?

Cheers,

[jean-paul]

Hi frank,

if you have some Silmics to test you can always send them.

Cheers,

Jean-Paul

[fdegrove]

Hi,

Sorry to say so,I don't have any fancy PSU caps...

Once again,try to find your fellow countryman's mistake by looking at the circuit diagram.

Also find me a manufacturer of elcos with shorting plates under fault condition since this can easily set the house on fire.

That is my only worry now JP.

Cheers,

[pinkmouse]

Also find me a manufacturer of elcos with shorting plates under fault condition since this can easily set the house on fire.

Not got any input fuses then, Frank? Naughty boy...