Rebuilding the Power Supply on a Vintage Amplifier
Part II: Let's Solder!Part III: Multican Capacitors
Multican capacitors: Now we come to the fun part. And buy fun, I mean kind of a pain in the ass, but also fun in the more traditional sense. On many old amplifiers, there are can-style capacitors with more than one capacitor capacitor section built into the enclosure. On the 1700, there are three total on the left side of the amp.
The three multican capacitors used in the MAC1700.
From the service manual, the specification of these are:
Part #066-093, multisection electrolytic: 200mf/500mf, -100VDC/-75VDC,
has three blade connectors, can is 3″ tall by 1 1/4″ Diam.
part #066-099, multisection electrolytic: 200mf/500mf, 100VDC/75VDC,
has two blade connectors, can is 2″ tall by 1 1/4″ diam.
part #066-103, multisection electrolytic: 80mf/80mf/150mf/50mf,
200VDC/200VDC/150VDC/150VDC, has four blade connectors, can is 3″ tall
by 1 1/4″ diam.
These are dead custom parts, and you’ll never find an exact match. Even if you found a NOS match, it wouldn’t be any good, because electrolytic capacitors degrade over time. So here’s what I did: I bought replacement capacitors matching the values of the individual sections, removed the cans, cut them open and removed the existing guts, and replaced them with the new capacitors. It’s a lot of work, but you end up with a brand new capacitor that looks exactly like stock, and is easy to work on if the need should ever arise. If you decide this isn’t for you, I did get a quote from these guys, and the price was extremely reasonable. Continue to page 3 for the step-by-step process.
Remove the Multisection Cans: It’s a pretty straightforward process. First, while the capacitor is still connected, take pictures and notes of how the pins are oriented/connected, and identify from your schematic which pins correspond to which capacitor section. Unsolder the wires, in the center of the can, and untwist the tabs around the perimeter to release it from the chassis. You’ll end up with something like this:
A multisection electrolytic capacitor.
Cut it Open: Carefully cut around the top of the can with a dremel or hacksaw, leaving about a 1/4″-1/2″ above the ridge at the bottom. I wrapped the can with tape, to use as a guide for cutting, like this:
Make your cut about 1/4" above the ridge where the can widens at the bottom.
You can throw away the guts (bottom right in the picture). The top part of the can may be filled with a tar-like goop. You can boil it in water to soften it and then scrape it out, but be forewarned that this will take the coat of paint off the part as well (the aluminum will expand in the boiling water, cracking and stretching the paint). You can repaint it later, or leave it as shiny aluminum, it looks fine either way I think.
The can after you have cut it open and removed the guts.
Connect the New Capacitors: You see the metal strips on the inside of the bottom section? Those are your electrical contacts. You can solder the new capacitors to those, but there’s not a lot to work with there and it seems to me that it would be a real pain to do it that way. I found a sturdier way to do it was the following.
Drill new holes for the capacitor leads to pass through right next to the electrical posts, like so. Remember you will also need a slightly larger hole for the grounds to pass through.
Drill a small hole right next to each electrical post, and another hole for ground.
Pass the leads of the capacitors through the appropriate holes. You should end up with something like this.
The capacitor leads threaded through the holes drilled in the previous step. Note that the (-) leads are passed through their own hole, by the square symbol.
The capacitor leads will probably not be long enough. You can solder extensions on them, and then wrap the leads with heatshrink tubing so that they won’t contact each other or the sides of the can.
If the capacitor leads aren't long enough, you can solder an extension onto them.
From the top, the can should look like the picture below. I reattached the top of the can by taking a strip of sheet metal about an inch wide by the circumference of the can. I laid this in around the inside of the bottom part of the can (remember when I told you to cut about a quarter inch from the flange at the bottom?). The springiness of the sheet metal was enough to hold the top part of the can firmly on, it looks completely stock, and I can easily remove it if I ever need to service what’s inside.
The new capacitors installed in the can. Note the scrap of sheet metal laid around the inside of the can, which holds the top of the can on.
Reinstall the cans, solder the leads in in the appropriate places, and you’re done! Your amp should provide many more years of faithful service.
Special thanks to the peeps over at the Audiokarma.org forums, who patiently answered all of my questions.
Go to Section:
- Part I: Prologue
- Part II: Let's Solder!
- Part III: Multican Capacitors
- View All
April 21st, 2009 at 3:05 pm
just found this and want to first say thanks. a lot of guys don’t appreciate what a deal it is not only to fix something, but then to write about it so that others may benefit. i’ve got a 1700 which has been giving trouble on one channel-scratchiness and breaking down at volume-so i figure it’s time to look into it. can’t find any schematics so far and as i don’t have the manual, i can’t verify the tubes and look for new ones(i have an old tube tester and it gives all but one tube the thumbs up). this article should be a big help as i try to fix what is a very nice piece of equipment-thanks again-any further info on this receiver would be appreciated.
April 21st, 2009 at 3:23 pm
Glad you find it helpful! Note that the signal only passes through the tube section when you’re using the FM tuner. So if your problem only occurs only when using the radio, it’s definitely a tube problem, otherwise it’s definitely a solid state problem. If you want to send me your e-mail address, I’ll send you my copy of the 1700 service manual (which includes schematics and parts lists).
May 6th, 2009 at 4:56 pm
i would really appreciate a copy of the service manual as i suspect that i may need more than a recapping with this unit. i used it for about a year and it was great-then i started to get a choppiness in the left channel, so i put it away for later attention. i was using some jbl’s with it, but now i have found some wharfedales which i want to try w/it. it’s a piece that gives one a nice sense of satisfaction to have in one’s system, so i’m gonna have to do what i can. i downloaded your parts list, but it is a .xsl(which i believe is a windows format) and i am a linux and mac osx guy, so i’ll have to see what i can do-if the manual is pdf, that would be great, but if not, i’d still be more than grateful to get it and i will do what is necessary to access it’s info-i have an old drive w/windows2000 which might do.
thanx again, over the years, i have looked up a lot of technical stuff and i can tell you that persons who know their stuff are rare, but people who know their stuff and can relate that knowledge to others clearly and effectively are a real find. thanx.
May 13th, 2009 at 3:36 pm
@dave: I sent a copy of the manual to the e-mail address you used to leave the comment. Send me an e-mail if you don’t get it.
August 15th, 2009 at 1:01 am
hope your leed thing turned out for you. i’m gradually working my way into the 1700 project(after some mixups with part shipments). i want to replace the diodes but can’t find replacements-if you did the ones on your unit, what did you use? the #’s appear to be westinghouse 3988′s and 1N4820′s. my keyboard seems to be messing up, so i hope you get this, and thank you for taking the time to respond. dave
August 20th, 2009 at 9:09 pm
Unfortunately, I can’t seem to find the part numbers that I used–I might have bought them at an Electronics Part Outlet, rather than online. But they’re just power rectification diodes, so as long as you equal or better the specs you’ll be fine.
The 1N4820 is easy because it turns up a datasheet with a Google search.
For the 3988, I’d just work from first principles. AC (I assume you’re in the US) is 120V, so there’s your reverse voltage. From the owner’s manual, you know that the max power draw is 270W = ~2.25A.
So if you find a ‘power’ or ‘rectification’ (not ‘signal’) diode rated for, say, 300V max reverse voltage and 3A forward current, you’re good. I think.
January 13th, 2010 at 11:21 pm
hi Max,
Great blog on DIY MAC1700 recap. I just bought one. I will do the recap using your guide. I would really appreciate a copy of your service manual, as a back up in case I ran into issues.
thanks in advance. Ken
January 16th, 2010 at 10:55 pm
Best of luck Ken, I just sent a copy of the owners and service manual to the address you used to leave a comment.
Hey for future people, if you want a the service or owner’s manual e-mail is probably a little better way to contact me, I don’t always see the comments right away. My e-mail address is in the “About Me” section.
April 23rd, 2010 at 8:19 am
Hi Max,
It was very kind of you to create and publish this website. It has been very educational for me.
I have a Mac 1700 textbook case of loud buzz at the speaker terminals and headphone output and about 3vDC as well. It just spontaniously happened yesterday after the unit had been on for about 8 hours. I have the schematic but not the service manual. If you would please email it to me I would really appreciate it. Also, I have a question. Would it be ok to disconnect the wires to the old cans and then put replacement caps in the chassis area underneath the old caps, rather than disassemble and rebuild the cans? Do you Think there would be room?
Thank you for all your help!
Kip
March 8th, 2011 at 8:25 am
Dear Max,
Great job here. I found this in a search looking for hints on repairing a MAC 1700. It belonged to my father in law. he gave it to my sister in law when he bought a MAC 4100 years ago. The 1700 got pretty well trashed by kids over the years (broken face plate, grime). Anyhow, the 4100 came to my family when Dad died and now the 1700 has come this way as well. This 1700 has a good working amp and preamp but the FM sounds horrible. My suspicion is tubes. I would really appreciate if you could send a copy of the service manual my way, can’t seem to find it anywhere else.
Thanks.
Dale
March 12th, 2011 at 12:46 pm
The manual is now posted here:
http://blog.wingedvictorydesign.com/wp-content/uploads/2009/03/MAC1700_ser.zip
Best of luck!