CJ

Re: Mica caps for high frequency EQ?
« Reply #20 on: February 11, 2018, 03:22:29 PM »
Mallory made some green caps
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Re: Mica caps for high frequency EQ?
« Reply #21 on: February 11, 2018, 03:37:17 PM »
Just a quick question for those in the know ,
Sometimes I pull apart old bits of electronic gear containing what looks like paper in oil caps ,these are mounted in a cardboard tube and wax dipped . Almost all of them show very poorly for leakage ,would gentle baking and then re dipping in wax bring these back to life ,could be moisture ingress thats made em go bad .

scott2000

Re: Mica caps for high frequency EQ?
« Reply #22 on: February 11, 2018, 04:16:56 PM »
Mallory made some green caps

They match the blue heater wires..... ;D

Nice caps!! Never seen those before....
« Last Edit: February 11, 2018, 04:22:50 PM by scott2000 »

Re: Mica caps for high frequency EQ?
« Reply #23 on: February 11, 2018, 05:36:46 PM »
The mullard mustard caps seem to have a great rep ,and very high prices too ,luckily I have a few trays of them in my component drawers . People tend to make wild and extravagant claims about sound differences of their personal favourites, one resin dipped foil cap isnt much different to the next in my opinion,you fast approach the law of diminishing returns the more money you spend .

scott2000

Re: Mica caps for high frequency EQ?
« Reply #24 on: February 11, 2018, 08:37:06 PM »
Not pico nano related but, I had an old Tango converter that I swapped some channel's 10uf  smd caps with some newer Panny FR through hole  and I could hear a pretty significant improvement ......or difference....... I had multiple channels so I was able to compare pretty easily........

Re: Mica caps for high frequency EQ?
« Reply #25 on: February 11, 2018, 08:42:52 PM »
Well yeah ,different game of soldiers all together with with electrolytics ,the values change as the electrolyte dries out .

Re: Mica caps for high frequency EQ?
« Reply #26 on: February 11, 2018, 11:04:40 PM »
Some of the newer electrolytics like the FR series are also inherently better as new, compared to the SMD electrolytic models from a decade ago. Along with the Panasonic FR series, the newer Panasonic FS series (size reduced) is nice, as is the United Chemi-Con KZN series. They all have very high ripple current ratings, very low impedance specs, and super long life (8-10kHr).

Sorry for the thread drift, but electrolytics are still important, and some of the new models are really superior.

Re: Mica caps for high frequency EQ?
« Reply #27 on: February 12, 2018, 03:00:17 AM »
Good point as well Monty,

I wonder has anybody found an application where these new more high performance electros have a negative impact on circuit performance . Aside from the obvious awkwardness of having to mount radials in a position meant for axials, does newer high performance low esr always bring benefits.

mjrippe

Re: Mica caps for high frequency EQ?
« Reply #28 on: February 12, 2018, 12:38:37 PM »
Just a quick question for those in the know ,
Sometimes I pull apart old bits of electronic gear containing what looks like paper in oil caps ,these are mounted in a cardboard tube and wax dipped . Almost all of them show very poorly for leakage ,would gentle baking and then re dipping in wax bring these back to life ,could be moisture ingress thats made em go bad .

Those are most likely paper and foil caps dipped in wax.  No oil.  Oil caps tend to have metal or plastic casings. 

shabtek

Re: Mica caps for high frequency EQ?
« Reply #29 on: February 12, 2018, 01:17:53 PM »
One could certainly try desiccating and  remeasuring leakage.
What is mechanism of leakage, dielectric breakdown? ...holes burned in paper?
"really fine players do not use stomp boxes or master volume, they match the amp to the room and turn it up to 11.  Stevie Ray, BB King, Albert King, Duane Allman, Dicky Betts, Louis Armstrong"
   -CJ


Re: Mica caps for high frequency EQ?
« Reply #30 on: February 12, 2018, 05:36:33 PM »
Come to think of it many paper in oils in the old days used contain PCB's and a wax seal on an oil impregnated cap is going to be a waste of time anyway, so I think your right there MJ.
I really dont fancy heating those things up in my oven where I cook food at any rate ,maybe on a radiator or heater of some kind
I dont know what the cause of the breakdown could be Shab,is it possible the foils may have oxidised and damaged the dielectric ,I guess even at a modest heat for some hours if its starts to show an improvement in leakage resistance it might be worth continuing ,could Rf be used to heat the cap from within to drive out the moisture while its still soldered  in an old radio ,or maybe that would be a good way to kill it off completely ,I dont know .

Has anyone tried reforming electrolytics ,I've heard about it but Ive never tried it ,I guess you have to be selective and not be bothered with anything showing signs of damaged seals or with stuff spueing out of them  . It weird cause some electros say in the psu of old valve radios can still be working after 50-60 or more years .

JohnRoberts

Re: Mica caps for high frequency EQ?
« Reply #31 on: February 13, 2018, 11:07:21 AM »
Come to think of it many paper in oils in the old days used contain PCB's and a wax seal on an oil impregnated cap is going to be a waste of time anyway, so I think your right there MJ.
I really dont fancy heating those things up in my oven where I cook food at any rate ,maybe on a radiator or heater of some kind
I dont know what the cause of the breakdown could be Shab,is it possible the foils may have oxidised and damaged the dielectric ,I guess even at a modest heat for some hours if its starts to show an improvement in leakage resistance it might be worth continuing ,could Rf be used to heat the cap from within to drive out the moisture while its still soldered  in an old radio ,or maybe that would be a good way to kill it off completely ,I dont know .

Has anyone tried reforming electrolytics ,I've heard about it but Ive never tried it ,I guess you have to be selective and not be bothered with anything showing signs of damaged seals or with stuff spueing out of them  . It weird cause some electros say in the psu of old valve radios can still be working after 50-60 or more years .
Reforming old caps is just a matter of slowly charging them up through a high impedance the limits the inrush current to prevent releasing smoke.  Of course if they never charge up to full rated voltage after a decent interval, trash them.

Back last century while at Peavey while managing slow moving inventory I discovered an old cache of large electrolytics. I considered reforming them, but decided against it. Life is too short to use components that already have one or two strikes against them, inside new products.

JR
John Roberts
http://circularscience.com
Tune it, or don't play it...

Whoops

Re: Mica caps for high frequency EQ?
« Reply #32 on: February 13, 2018, 11:27:16 AM »
It weird cause some electros say in the psu of old valve radios can still be working after 50-60 or more years .

Yes but how well are they filtering after 60 years?

And are you safe to say they will not blow soon and damage other components?

How far are them form dying completely tomorrow?

rackmonkey

Re: Mica caps for high frequency EQ?
« Reply #33 on: February 13, 2018, 04:33:11 PM »
I reform old aluminum can type electrolytics pretty frequently.  Success rate is just good enough to keep me doing it, i’d say about 50 - 60%. If they aren’t sealed well and have dried out, forget it. But I have brought back caps that were 200% off their nominal capacitance with 50% or more leakage and horrid ESR values. I use A Lab Volt 400V variable power supply and a 10000 ohm wirewound resistor rated for the task to reform high voltage electros for tube gear. Monitor voltage and current across the cap, and voltage across the resistor. Bring the variable supply up until you get to 10 volts or so. Check cap current. If it’s not acting like a short, slowly bring up the voltage until you get to about 50 volts. The cap voltage will slowly go up while V across the resistor goes down. It might take hours for the V across the resistor fall by half. When it does, bring up the voltage to 100 V and repeat. Continue until the voltage across the cap is close or equal to its rated voltage.  It has taken up to 10 or more hours to do one cap, so it’s not something to start if you’re in a hurry. I wouldn’t leave the house while you’re doing it, either. You want to be there to monitor it in case the cap hits the wall and starts overheating.

Forget old Sangamo cans. Never had a bad one even start to reform. Old Mallorys and Spragues work often as not.

Funny you bring this up. I do this enough that i’m tired of spending the time on it, and  bought a PCB from Silicon Chip magazine in Australia. They had an article I found online about a nifty automated reformer that does the whole process. They had a few PCBs left from 2010 when the article came out, so I bought one for something like $13. Just finished programming the chip for the LCD display about a week ago. Even have to wind your own little 20:1 transformer for it. We’ll see how it works.

EDIT:

I’ll warn you, it’s not really something sensible people do. I felt like the dolt I am after getting through 2 of the 3 caps in a multi-cap can, only to find that the third one (I needed it) was effed and beyond undead status.  Had to buy the part.

BT
« Last Edit: February 13, 2018, 04:52:14 PM by rackmonkey »
Whether you think you can or you think you can't, you're probably right.

Re: Mica caps for high frequency EQ?
« Reply #34 on: February 13, 2018, 05:26:41 PM »
Thanks for that Rackmonkey ,I'll have to look into the situation some more .

JohnRoberts

Re: Mica caps for high frequency EQ?
« Reply #35 on: February 14, 2018, 10:10:09 AM »
Back last century I encountered a production problem with a batch of brand new electrolytic capacitors. These were used for Phantom voltage blocking in a mic preamp front end. These particular caps were rejected because they were noisy (probably from elevated current leakage). In a high volume production environment things move quickly so I just blackballed that entire series of capacitors and replaced them with quiet (normal ones).

 In hindsight these brand new caps may have come from the capacitor manufacturer insufficiently formed in. It is entirely possible that over time these caps would have quieted down by themselves, a luxury we didn't enjoy running at factory speed. Not my job to diagnose the vendor's problems (while that happened often enough).

JR 
John Roberts
http://circularscience.com
Tune it, or don't play it...

rackmonkey

Re: Mica caps for high frequency EQ?
« Reply #36 on: February 14, 2018, 11:45:42 AM »
In a production environment with product (and to a degree) company reputation on the line, it was the right call IMO. Initial impressions by the customer are critical. Too bad more manufacturers don't think that way.
Whether you think you can or you think you can't, you're probably right.