|
Audio Asylum Thread Printer Get a view of an entire thread on one page |
For Sale Ads |
200.123.215.113
In Reply to: RE: Voltage rating for coupling cap posted by Tweaker456 on March 23, 2016 at 07:52:30
Without a schematic it is speculation to give a definitive answer, but in general it should be assumed that it is necessary to use a coupling cap with a voltage rating equal to the supply voltage. Before the tube conducts there will be a voltage equal to the supply voltage on the coupling capacitor. You can check this for yourself by attaching your DVM in parallel between the plate side of the cap and ground. Power up the circuit and see how high the voltage goes before the tube conducts.
Follow Ups:
The designer of the amp got back to me stating that upon turn on there is 300 to 350 volts across the coupling caps and says the rating should be 400v. His agent misspoke about the 250v value, followed through and came up with the 400v rating. Thanks, Tweaker
Palustris, Thanks for the informative response that very much looks like it is the correct useful answer to my question. Puzzles me why someone with electronics training would think it ok to go close to the 70v rating at 100v though. Tweaker
Edits: 03/23/16
Some capacitors can take the momentary overload, is probably why. But I agree with Palustris. What he says is the best safe practice. On one occasion, I have cheated on this rule by a bit and so far have gotten away with it, but I don't recommend it.
If you add a B+ delay circuit the over voltage on start-up can be avoided.
"It is better to remain silent and thought a fool, then speak and remove all doubt." A. Lincoln
What, Me remain silent? I don't think so. Love the quote. I'll play it safe and go with 250v or at least 200v in my old age. Tweaker
Edits: 03/23/16
Yes, I was about to write that when someone walked into my office, which reminded me that I was at work. Only a temporary aberration.
Sadly, all too few tube components are built that way. Mine are, because I've modified them.
The schematic and the designer show and say 70v. A well know audio electronics person says 100v will do, the designer recommendes 250v min.
The schematic and the designer show and say 70v
the designer recommendes 250v min.
Someone has miscommunicated. Not good on a BBS
ET
I guess that was unclear. The schematic says 70v and the designer in an email says there is 70v there. The designer recommends a 250v cap in that place where there is 70v. Someone posted that there can be the total PS voltage there for a brief time, 180v. That explanation makes sense. What doesn't make sense is why another electronics savvy person who looked at the schematic said that a 100v cap was ok. I see no contradiction, just maybe not clear enough. The brief total PS voltage of 180v in that spot should explain it. Let me know if I commited any other crime Awe-d. Tweaker
Post a Followup:
FAQ |
Post a Message! |
Forgot Password? |
|
||||||||||||||
|
This post is made possible by the generous support of people like you and our sponsors: