A question of PIO capacitors on coupling. I found that the caps coupling from driver tube at 320vdc to the 300B in cathode bias, the grid shows a positive voltage on 3 volts! (it shoud be zero), but the sound seems OK, does this will destroy or impair the full function of the power tube or the sound? More, even between voltage tube to driver tube, the cap a 0.lmf/630v coupling from 150v also shows up 1.2v on the grid of the driver tube also in cathode bias. It concerns me on using the PIO caps because the polysterene type doesn't shown like that!!! Please help....
Thank you Chris, that means it is dangerous to let it run like that.
It is strange, these oil caps of good reputation brand and happen this fault, I lost money trying to upgrade. So, anyone please take care on buying paper in oil caps on this concern. But, when ordering through the mail, I have no way to check its condition. Before soldering to the circuit, I used the 10K setting on the ohmmeter to check it n found only very slow discharge to zero, but after soldering it shows up leaky voltage!!!!
Do someone have this nasty experience?
I try to return to seller, but, they say I passed the warranty time!!
Anyway, loss big bucks...pity
It is strange, these oil caps of good reputation brand and happen this fault, I lost money trying to upgrade. So, anyone please take care on buying paper in oil caps on this concern. But, when ordering through the mail, I have no way to check its condition. Before soldering to the circuit, I used the 10K setting on the ohmmeter to check it n found only very slow discharge to zero, but after soldering it shows up leaky voltage!!!!
Do someone have this nasty experience?
I try to return to seller, but, they say I passed the warranty time!!
Anyway, loss big bucks...pity
I really hate to tell you this, Tubesin, but you wuz had. Paper-in-oil is just so 19th century! Even by the early 1890's, PIO capacitors had largely been abandoned in favor of the much higher Q mica capacitors for just about everything, except for apps requiring very large capacitors (motor start/run caps.). PIO's have always had potential leakage problems. Not so critical for a motor start cap, but disasterous where you're counting on these things to protect your precious VTs. Sure, the 300B's might not mind that slight positive bias now, but rest assured, this situation will not improve with age.
When various capacitors were actually put to the test, PIO really did not test out all that well. Perhaps better than ceramics (e.g. Sprague "Orange Drops") but not by much. You'd do considerably better with metal film polypropylenes, such as AuriCaps. (And, no, I'm not connected with them in any way, shape, or form, other than as a satisfied customer.)
This is the only test I could find comparing PIO to other caps. Rudimentary for sure:
http://members.aol.com/sbench102/caps.html
I'd be interested in seeing others.
http://members.aol.com/sbench102/caps.html
I'd be interested in seeing others.
Interesting. Still, the polyprop's come off pretty good. However, I haven't seen any PIO's that didn't show some resistance when checking them out with a digital multimeter. That usually came to about 1.0 -- 3.0MEG. Just enough to make a nice voltage divider between a plate and next stage grid resistor. Use the PIOs for PS bypass caps, not interstage coupling caps.
Yes, and when the PIO's start to run warm, yank them. They will eventually dry out in a few years anyway. Solen Fast caps might be the way to go, but any decent plastic foil will make you much happier.
Miles,
Sprague "Orange Drops" are metalized plastic are they not? Generally I avoid ceramics all together.
-Chris
Miles,
Sprague "Orange Drops" are metalized plastic are they not? Generally I avoid ceramics all together.
-Chris
To test coupling capacitors, you really need a Megger. An ordinary DVM only applies a couple of volts across the capacitor (which may not be enough to provoke leakage), whereas a Megger typically applies 500V. Anything that shows >100M of resistance whilst withstanding 500V is probably OK. Most of the PIO capacitors I've tested failed this test.
I wonder how much of this is due to specific construction deails. The pile of glass and steel encased 0.1 uF K40Y-9 PIO caps in my spares box all measure -OL- on a Fluke. Re: oil leakage, I recently decommissioned a large, early nineties, ferro-resonant UPS which used a bank of 660 volt GE dielektrol poly-oil caps as part of the resonant tank. It was surprising to see most had a small ring of seepage around the terminals. Admittedly they get pounded pretty hard in this application. This type of leakage might still be more a property of oil caps in general than paper specifically. Certainly the paper-oil caps in some transmitters I maintained literally lasted generations at thousands of volts. I wish electrolytics came close.
If it's leakage current, what's the best way to check? Bias at high voltage with a series resistor and measure for drop across the latter? I'm also playing around with a grid-biased E180F on the front end of an EL84 SE. It's a simple matter to swap out the input coupling caps with different types and see if the plate voltage changes.
Finally, if you want to really go to the extreme:
http://www.soundlabsgroup.com.au/audioconsulting/audio_consulting_capacitors.htm
72 mohm for a 10 uF at 40 kHz is pretty impressive, though not an such at insane price. Or maybe more impressive they find customers.
This isn't all to say that PIO caps are the best (in fact I find the K40Y-9's a bit bright) or even top ten. I'm just not totally convinced the objections raised are due to fundamental properties of PIO rather than specific implementation. I'm hope to find some hard data related to their performance.
(PS - I think 715 Orange drops are metalized, 716 film and foil.)
If it's leakage current, what's the best way to check? Bias at high voltage with a series resistor and measure for drop across the latter? I'm also playing around with a grid-biased E180F on the front end of an EL84 SE. It's a simple matter to swap out the input coupling caps with different types and see if the plate voltage changes.
Finally, if you want to really go to the extreme:
http://www.soundlabsgroup.com.au/audioconsulting/audio_consulting_capacitors.htm
72 mohm for a 10 uF at 40 kHz is pretty impressive, though not an such at insane price. Or maybe more impressive they find customers.
This isn't all to say that PIO caps are the best (in fact I find the K40Y-9's a bit bright) or even top ten. I'm just not totally convinced the objections raised are due to fundamental properties of PIO rather than specific implementation. I'm hope to find some hard data related to their performance.
(PS - I think 715 Orange drops are metalized, 716 film and foil.)
I guess they may not be made well. Too delicate.
EC8010,
You are quite right. HV caps need to be tested at a higher voltage.
In circuit I measure the cold end voltage. Out of circuit I will use an old Heathkit cap checker that applies a few hundred volts across the cap. I always use an HP 4263A to test as well, by lifting one end of the cap.
This gives me a good idea how the rest of the caps are doing.
-Chris
EC8010,
You are quite right. HV caps need to be tested at a higher voltage.
In circuit I measure the cold end voltage. Out of circuit I will use an old Heathkit cap checker that applies a few hundred volts across the cap. I always use an HP 4263A to test as well, by lifting one end of the cap.
This gives me a good idea how the rest of the caps are doing.
-Chris
Absolutely. Audiophile capacitors should be hand-rolled on the thighs of Cuban maidens in an inert atmosphere using oxygen-free gold leaf with polyputheketlon dielectric and terminated with 6 nines Italian silver solid wires of exactly 0.7071mm diameter.
Alternatively, polypropylene/foil capacitors are jolly good and those Soviet Teflons are even better (although rather large).
Alternatively, polypropylene/foil capacitors are jolly good and those Soviet Teflons are even better (although rather large).
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