Can anyone comment on these:
http://cgi.ebay.com/ws/eBayISAPI.dl...3225&ssPageName=MERC_VIC_ReBay_Pr4_PcY_BIN_IT
Supposedly they are Sprague brand motor run caps. I bought a few 50uf and 7.5uf as they met the specs.
http://cgi.ebay.com/ws/eBayISAPI.dl...3225&ssPageName=MERC_VIC_ReBay_Pr4_PcY_BIN_IT
Supposedly they are Sprague brand motor run caps. I bought a few 50uf and 7.5uf as they met the specs.
I just checked one of the 100uf ASC's out of the case of 25 that I got from Midori last week. Shaved one of the terminals with an exacto knife to see what was under the plating. The terminals are brass.
On the DC voltage rating they may be OK for higher than the 525 that Midori specs them for (your on your own if you try this...). Basis for this statement is based on the voltage rating for the last batch of 40uf 440 volt GE caps (97F5116F) I got from Allied. The GE's are rated for 440Vac and 1000Vdc, a ratio of 2.27x, quite a bit higher than the 1.414x usually used. Could be that DC operation is much less stressfull than AC operation.
Using the same ratio on the ASC's that GE uses the 370 volt caps convert to 840 volts DC.
I've also got some GE 8uf (23F1039G2) caps that are rated for 660Vac or 1500 Vdc which calculates out to the same 2.27x ratio.
I'm going to stick a pair in my modified Stromburg-Carlson PP 6550 amps that are doing subwoofer duties at this time. They run a B+ of 635V. We'll see if any smoke comes out...
Gary
On the DC voltage rating they may be OK for higher than the 525 that Midori specs them for (your on your own if you try this...). Basis for this statement is based on the voltage rating for the last batch of 40uf 440 volt GE caps (97F5116F) I got from Allied. The GE's are rated for 440Vac and 1000Vdc, a ratio of 2.27x, quite a bit higher than the 1.414x usually used. Could be that DC operation is much less stressfull than AC operation.
Using the same ratio on the ASC's that GE uses the 370 volt caps convert to 840 volts DC.
I've also got some GE 8uf (23F1039G2) caps that are rated for 660Vac or 1500 Vdc which calculates out to the same 2.27x ratio.
I'm going to stick a pair in my modified Stromburg-Carlson PP 6550 amps that are doing subwoofer duties at this time. They run a B+ of 635V. We'll see if any smoke comes out...
Gary
In the original intended application (motor run) the cap is used to create a phase shift for one of the windings in an AC motor. Some serious AC current flows through the capacitor. There is also a voltage across the capacitor. Since we now have a capacitance and an inductance (the motor winding) in series across the AC line, we have the desired phase shift. This means that the voltage and the current on the capacitor are not in phase with each other. It also means that 1.414 does not necessarilly apply.
Back to tube land. In a tube amplifier the first cap in the power supply has to deal with all of the ripple current and usually sees the highest voltage so it gets the most stress. The last cap in the power supply in a SE amp sees all of the signal current for both channels. These currents are in phase and add up for bass signals. The last cap in the power supply for a P-P amp provides the peak current demands for both channels. The parafeed cap sees the signal current for one channel.
The point here is that the lower the current demands are on a capacitor, the higher the voltage that you can apply to it. Just where the limit is is hard to say. Be warned that things may get ugly when the limit is found. Motor run caps are made to handle high currents, and thus have a low ESR (that is why we like them). If the power supply can source a lot of current (big transformer, SS rectifier) it is possible for the cap to explode.
Back to tube land. In a tube amplifier the first cap in the power supply has to deal with all of the ripple current and usually sees the highest voltage so it gets the most stress. The last cap in the power supply in a SE amp sees all of the signal current for both channels. These currents are in phase and add up for bass signals. The last cap in the power supply for a P-P amp provides the peak current demands for both channels. The parafeed cap sees the signal current for one channel.
The point here is that the lower the current demands are on a capacitor, the higher the voltage that you can apply to it. Just where the limit is is hard to say. Be warned that things may get ugly when the limit is found. Motor run caps are made to handle high currents, and thus have a low ESR (that is why we like them). If the power supply can source a lot of current (big transformer, SS rectifier) it is possible for the cap to explode.
tubelab.com said:
Hmmmm, something about your sig gives me the impression you didn't write this 'in theory'. 😀
I personally saw a 10 KV oil cap short, blow one of the terminals off and spray steaming hot oil all over the inside of a 3KW Gates shortwave transmitter. There was no other fault condition. Just a 20 year old cap that did not like being awakened form a long sleep. I was across the room (at least 20 feet away) and it still scared the **** out of me.
I have seen my share of electrolytics explode, but I have not seen a motor run cap fail catastrophically........Yet. The one in my air conditoner just died a silent death.
I have seen my share of electrolytics explode, but I have not seen a motor run cap fail catastrophically........Yet. The one in my air conditoner just died a silent death.
Never had the dubious pleasure of seeing one go but once cleaned up the aftermath. A case of lightning strike meets Harris MW-50, a nasty transmitter with a 100 kwatt, 20 kV DC supply.
Everybody's been discussing these wonderful PS and bypass caps, what do you guys use for coupling caps?
leadbelly said:
I like AuriCaps. I replaced a 1.0uF electrolytic coupling capacitor in a solid state amp I built with a 1.0uF AuriCap, and that made a big difference in how it sounded. Much clearer and more detailed. Although that isn't always a good thing in that every defect in a bad mp3 now comes through loud and clear. Even some of the early CDs I have sound a bit "off".
Even though AuriCaps are a bit more expensive than your run-of-the-mill capacitors, they aren't outrageously so.
leadbelly said:
I'll second the Auricap. I put them in my amps and really like them. I replaced the Solen coupling caps in another amp I built with Auricaps and found an improvement in doing so.
Nice quality and not too overpriced.
Thanks for the tip. Any fans of transformer coupling in the audience? How does iron compare to boutique caps for coupling?
leadbelly said:
I've been avoiding it, but am rethinking this. Here's A Thread over in the Solid State forum where they were discussing this concept.
If you're gonna go the xfmr route, best make certain that you get good iron. That's not the place to go cheap, and really good xfmrs certainly aren't cheap.
Cheap iron ==
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sonics.Regarding coupling caps: If there is room on the chassis, what do you guys think of these ASC (or other) PIO caps for coupling? I've read others like PIO caps for coupling as they sound 'smoother'. But I'm a newbie, so I really don't know any better. Are there any preferable sonic (or other) differences of PIO over the Auricaps, BlackGates, etc....?
Also, can't find 47uf and 100uf Auricaps. You guys have other GOOD suggestions?
Protos,
Thanks for the info.
I recently bought a pair of Dynaco Mk IIIs. My idea was to "borrow" the iron to play with. The B+ on the original Dynaco circuit stabilizes at 480 V. However, while warming-up, the voltages on the power supply caps reach up to 525 to 585 V. Your experience suggests that at least these caps won't blow up the first time I turn it on!
Gary,
Please let us know the results of your smoke test. Enquiring minds want to know! If you can run these reliably at 635 V, I would feel much better about my warm-up voltages.
Tubelab,
As usual, you added an insight that makes sense once I read it, but would not have seen on my own. I think I’ll take your lead and invest in that sheet of Plexiglas… just in case. 😱
I'm going to be a NewB for a while.
Looney
Thanks for the info.
I recently bought a pair of Dynaco Mk IIIs. My idea was to "borrow" the iron to play with. The B+ on the original Dynaco circuit stabilizes at 480 V. However, while warming-up, the voltages on the power supply caps reach up to 525 to 585 V. Your experience suggests that at least these caps won't blow up the first time I turn it on!
Gary,
Please let us know the results of your smoke test. Enquiring minds want to know! If you can run these reliably at 635 V, I would feel much better about my warm-up voltages.
Tubelab,
As usual, you added an insight that makes sense once I read it, but would not have seen on my own. I think I’ll take your lead and invest in that sheet of Plexiglas… just in case. 😱
I'm going to be a NewB for a while.
Looney
In my PowerDrive circuit the capacitor sees a constant resistive load, so the cap choice is not as critical as it is in a normal design. I use Malory or Panasonic film caps for most amps. For high dollar designs, I use Auricaps. They do make a difference.
Also, can't find 47uf and 100uf Auricaps. You guys have other GOOD suggestions?
If you need a high quality cap at these values, your probably going to be looking at motor run caps. Anything not metallized will be huge, and metallized caps wont be small.
If you need a high quality cap at these values, your probably going to be looking at motor run caps. Anything not metallized will be huge, and metallized caps wont be small.
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