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    Oil Filled Caps

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    harpy

    Posts : 94
    Join date : 2012-02-04

    Oil Filled Caps

    Post by harpy on Mon Feb 20, 2012 12:04 am

    I replaced all the electrolytic caps in my MK-IV's (quad and bias) and I was looking at the caps on the circuit board. What is the life span on those? They look like original caps. I am not really interested in upgrading the circuit board and am happy with the sound, but want some long term service and to be sure everything is close to spec.
    Would be replacing them with new oil filled caps retain the original sound or would a modern cap be better suited?

    Thanks,
    Jim

    Bob Latino
    Admin

    Posts : 2411
    Join date : 2008-11-26
    Location : Massachusetts

    Re: Oil Filled Caps

    Post by Bob Latino on Mon Feb 20, 2012 12:11 pm

    Hi Jim,

    I like the Russian PIO caps to replace the interstage and main coupling caps. If you do, you should probably use the Russian K42-Y caps because the K40-Y's are a little larger and may not fit in there on the STOCK board. You could also use, for a little less money, the SBE "orange drop" 716P caps. Antique Electronic Supply sells them. They are about $1.50 each but you only need 6 (3 on each amp) so it's not that expensive ..

    You can also go up one size in caps. Replace the four .10 uF caps with .22 uF and the two .05 uF caps with .10 uF caps. Just make sure that all the caps are 400 volt rated or higher.

    Bob

    harpy

    Posts : 94
    Join date : 2012-02-04

    Re: Oil Filled Caps

    Post by harpy on Tue Feb 21, 2012 12:16 am

    Thanks Bob, wonderful advice. I went with the K42-Y as there dimensions are very close with the stock ones. Went with the 630v .10's and 1000v .047's plus a set of smaller 400v just in case. They are coming from Russia with each set being matched.

    harpy

    Posts : 94
    Join date : 2012-02-04

    Re: Oil Filled Caps

    Post by harpy on Sat Feb 25, 2012 6:40 pm



    I bought some K40Y-9's .1 uf 630v and .047 uf 400v in the non conductive paint. I meant to buy the k42's, but K40Y will fit. I was reading Bill Thomas's ST-70 rebuilt post and saw this:

    "You've heard horror stories about how fragile the driver board is. Those stories are MORE than true. Even using the most *careful* de-soldering equipment and procedures, there was *slight* evidence of two isolated trace pads beginning to lift!"


    Does anyone have any tips for a successful installation? Soldering wattage etc.

    Thanks,
    Jim

    Bob Latino
    Admin

    Posts : 2411
    Join date : 2008-11-26
    Location : Massachusetts

    Re: Oil Filled Caps

    Post by Bob Latino on Sat Feb 25, 2012 7:25 pm

    Hi Jim,

    Bill Thomas is quite correct. Many times a solder trace will lift on an original ST-70 board. Just be careful and use as little heat as possible when you replace parts on an original ST-70 board.

    Everyone will have their own opinion but I like about a 30 watt soldering pencil for soldering parts on to a printed circuit board. Even an inexpensive Radio Shack 30 watt pencil will work OK. That same 30 watt pencil, however, may be a little "underpowered" for some chassis connections. You could also have a 60 watt pencil plugged in and use the larger pencil for the chassis connections.

    An all around solution is to get a soldering station that will let you turn up the heat a little when you need a little more power for some of the chassis connections.

    Bob

    GP49

    Posts : 733
    Join date : 2009-04-30
    Location : East of the sun and west of the moon

    Re: Oil Filled Caps

    Post by GP49 on Sun Feb 26, 2012 8:08 pm

    You might think about cutting the leads to the component being replaced, ABOVE the board and as close as you can to the component (presumably you are going to discard it anyway). Using needle nosed pliers, make small loops in the remaining leads. Crimp and solder those loops to the leads of the new component.

    This way you do not apply heat directly to the fragile foils on the circuit board.

    harpy

    Posts : 94
    Join date : 2012-02-04

    Re: Oil Filled Caps

    Post by harpy on Sun Feb 26, 2012 9:03 pm

    Thanks for the advice Bob and GP49,

    I heated the leads from above board and pulled them through the hole. I took a carbide drill the size of new cap leads and hand drilled through the board holes to clean up the solder the came up with the leads. The caps were dropped in with the leads extended through the little cones of solder. It was easy to quickly solder in place with a quick touch of the iron, then trim the leads. I checked continuity along the circuit board paths just to be sure.



    The K40Y-9 .047uf 400v fits with leads bent down right off can. There was some room to spare with the .1 uf 630v. Don't know if it matters, but the .1uf were matched and the .047uf were similar values (49 and 50).


    heyraz

    Posts : 58
    Join date : 2011-10-26

    Re: Oil Filled Caps

    Post by heyraz on Mon Feb 27, 2012 1:23 am

    First, I cut the component's lead close to the board. Yes, it wastes the component, but you'll apply less heat while desoldering that would have otherwise traveled into the component. I've had very good luck using a light coat of flux on the pad and picking up the solder with desoldering braid and a 20 watt iron. I've tried other methods before, but this one seems to be least damaging and extremely quick. Anything still remaining in the hole that isn't wicked up by the braid can be gently pushed thru with a dental pick heated by the soldering iron. Most important: clean up any left over flux with alcohol during all steps. After everything is resoldered back in place, clean again. It may look great now, but in a month it will be disgusting. There are also some excellent tutorial videos on youtube that you should watch. Practice makes perfect, you may want to try different methods on a busted vcr or something similar.

    harpy

    Posts : 94
    Join date : 2012-02-04

    Re: Oil Filled Caps

    Post by harpy on Mon Feb 27, 2012 10:59 pm

    Thanks Heyraz,

    I like your dental pick idea. I think my method gives a better change for a cold solder joint too, so I'll look at everything very closely and reclean. Then I am going to cage them up and keep my grubby paws off of them (I hope).
    The caps do sound wonderful though. A very nice upgrade.

    heyraz

    Posts : 58
    Join date : 2011-10-26

    Re: Oil Filled Caps

    Post by heyraz on Mon Feb 27, 2012 11:22 pm

    Another thing I do is clean each lead with steel wool before soldering-it improves success.

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