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Gent,I would first like to convey my most gratuitous appreciation for your help. Over the years I have asked a few questions on this forum you gents have provide wonderful insight. Perhaps someday I’ll grow beyond my “consumer” status on this forum. For now, I remain a consumer and really would like some help.
I have a Cary 572 and would like to replace the 100uf 50v OEM cathode bias capacitor with a Black Gate. Unfortunately, this value Black Gate doesn’t seem to exist. However, there is a 100uf 6.3v Black Gate NX series capacitor. Will this be sufficient? Alternately, I could use a 100uf 16v Black Gate N series capacitor.
The potentially pertinent info is thus:
- I checked the voltage at idle and found 2.35 volts DC across this capacitor
- The amplifier has a tube rectifier and a separate switch for heater and B+ voltage during turn on. I use them appropriately.
- I don’t mind experimenting with the 6.3volt capacitor and creating some smoke, but I don’t want “cascading” damage in the amplifier if/when it blows.What do you gents recommend?
Thanks,
Dave Ellis
Follow Ups:
Check out the tube curves. With a 2K cathode resistor you'd need over 3mA to develop 6.3V across the cap and that ain't ever gonna happen unless the B+ was somewhere near a KV! I'm assuming a simple grounded cathode stage here.Rgds,
Naz
Thanks much,"I'm assuming a simple grounded cathode stage here."
Yep, it's a simple grounded cathode stage.
Groovy,
Dave
This capacitor is bypassing a cathode resistor. The cathode resistor is not on your output stage, am I correct? It is on your input or driver stage?
Thanks for responding!"This capacitor is bypassing a cathode resistor"
Yep - exactly.
"The cathode resistor is not on your output stage, am I correct? It is on your input or driver stage?"
It's on the input stage - a 6SL7 tube.
Also, the resistor is 2.0k ohms - if this helps.
Dave
I would make a remote judgement in this case and say that the 6.3V cap would be fine. With a 6SL7, the most voltage you can expect across that cap in this lifecycle (or any other) is about 4V. If you want to be bulletproof, go for that next voltage. Some guys say to derate electrolytic caps some, and some say that's not such a good idea, sonically, on account of noise and stuff.The thing is, that cap goes, you're not gonna have a mushroom cloud in your listening room. The only thing will happen, the bass is going to go away.
Don't sic your lawyer on me for this, okay?
Aloha,
The thing is, that cap goes, you're not gonna have a mushroom cloud in your listening room. The only thing will happen, the bass is going to go away.No cloud, but a lot of stink and smoke and goo sprayed all over. If it blows it will smell for days -- weeks even.
A very small lot of stink and smoke, and other stuff you do not approve of sprayed over a little of the chassis. The smell is of burnt plastic, to which we are well accustomed, if we are experimenters, and lasts for hours, not days.I can sense that you not an experimenter. No?
I was just reliving the 2200uF 63V cap that blew (violently) on a breadboard and sprayed the room. That stunk for weeks.
I find that I owe you an apology. I am guilty of name-calling on a forum, a trait I consider typical of dirt . . . never mind, another name. Yes, it was done, ah, circumfrentially (I sense you are not an experimenter . . .), but was done nonetheless.I see you are an experimenter, even if you are, ahem, maybe a little more intolerant of the aroma of deceased capacitor in the listening room than I anticipated. Tastes differ. Well, you don't have to file it away intentionally in long term memory. Don't worry, if you remain an experimenter, your memory will be periodically refreshed (maybe you already know this as well).
Once again I must put a PostIt up in the corner of the screen saying 'Poinz; third glass of wine, do not hit 'submit'
Sorry about that,
That was the insight I was seeking! I certainly don't mind experimenting with this, and find it very comforting the only detriment will be a blown capacitor if the voltage is too high. I didn't know if the blown capacitor would also destroy other components in the amplifier.I am familiar with the smell of blow capacitors. In my younger years in the Army I was a Patriot Missile System technician. There were 3-4 capacitors/filters at the front of the RADAR. Invariably, one of these would blow every 3-5 months. The smell was quite pronounced, and he mess was profound. But, these were huge friggin capacitors I don't know the value, but they were the size of a kids shoe-box and cased in metal. Anyhow, the experiment will happen in my workshop - not in the living room.
Thanks very much for responding!
Dave
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