Rule of thumb. anything from before 1987 need the electrolytics changed especially on psu's.
I think it is relatively safe to wait for them to fail on Mellotrons. I have looked at my SMS card and it seems to be made in what we would call medical or milspec quality which translates to longer service intervals, but you will kick the crap out of almost any electronics laying back on cap service especially ARP and EMS synths.
gw
On Dec 4, 2007 8:32 AM, <jkorb@ix.netcom.com> wrote:
-----Original Message-----
From: tronbros@aol.com
Sent: Dec 4, 2007 7:55 AM
To: newmellotrongroup@yahoogroups.com
Subject: Re: [newmellotrongroup] Capacitor Source?John,In a message dated 04/12/2007 12:11:47 GMT Standard Time, astroboy@cinci.rr.com writes:Is there a current source for those big blue Caps in the M400 Power
Supply, 1600 and 2500uF - 40 volt, respectively? I've spent the weekend
trying to track some down, and while I can match the capacitance and
voltage, they don't come anywhere near the size of fitting in the
mounting straps of the originals.I know this will be a bitter pill so you had better sit down. Wait for it...................they don't make the blue ones anymore....................and...............you are going to have to change the straps on the SMS2. There was no other way to break it to you. Pour yourself a stiff Frank Stickle and relax.Best, - MartinGreetings John,Martin and Gang,Modern electrolytic capacitors are about 1/3 to 1/5 their original size,with much improved internal construction over their 1960s-1970s versions.Due in most part by the huge need for high-quality filter caps usedin computer power-packs.Anyway, from tech/eng'g. viewpoint, you can substitute a largercap value or higher DC working voltage ,but NOT the inverse.Higher capacitance translates to less AC power-pack ripple.I automatically replaced all paper/wax/foil capacitors on two antiqueTV sets and three valve-based radios in the last 1.5 years.You'll see these fully functional units on forthcoming MONEYPIT pages.Mellotrons, like other electronic bits of vintage technology WILLrequire all caps replaced.You'll have to wrap some tape around the base of replacement caps,to secure them within the original clamps. I use paper masking tape,as the plastic variety sometimes "slides" when clamed tightly.In 2006, I decided to replace all 40+ yr.old power-pack capacitors withinMK-I #124 "Julia." Result is a stable DC power-source , and muchquieter than before (85% reduction). KL has clearly heard these resultsduring our last two MONEYPIT gatherings.Hope this helps. Good Luck ! -- Jerry Korb ( at the capacitor ranch )