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TomB
08-21-2008, 05:26 PM
I have a pair of Monitor 7B speakers that I purchased new in 1981. I've used them fairly regularly over the years, except for a few years that they spent in storage.

In reading other posts, I get the impression that capacitor replacement on a
7B of this vintage is considered almost "routine maintenance." Is that really the case? Is there something I should listen for, to know for sure?

Granted, they don't seem to have the same "wow" factor that they had twenty-seven years ago, but I was attributing that to my nearly fifty-year-old ears.

I'm fairly handy, but I don't relish the idea of taking a soldering iron to these speakers.

Is there anything else maintenance wise that needs to be considered? The drivers are working, and everything looks like new.

If there's another post or thread that deals with this issue, please direct me there. I hate to cover the same ground that's been covered elsewhere.

Thanks for your help.

ben62670
08-21-2008, 05:34 PM
The original caps weren't the best in the first place. Then add 20 years to them, and they start to dry. New caps will yield better SQ in nearly every aspect of their performance. Have the single tweeter single driver makes the upgrade that much easier, and cheaper.
Enjoy
Ben

george daniel
08-21-2008, 05:47 PM
7b's are a relatively easy speaker to re-cap,I did two pairs last year,and if you're gonna' do it,,might I suggest that you replace the caps and resistors with quality parts,as it seems like you plan to keep them.You can do a search and find quite a few opinions on caps/resistors,if it were me,I'd go wilth mills resistors and sonicaps,and BAM,, you're good to go for another 20 years,put an integrated tube amp in the mix,and you might not ever have to leave your house again :D. Good luck,have fun and enjoy. :)

zingo
08-21-2008, 06:18 PM
I like other here have also rebuilt crossovers with much success. Parts Express is a great place to get parts and it's where I get mine. It's a great upgrade and feel free to post any more specific questions that you have.

TomB
08-22-2008, 09:46 AM
Thanks for the information. I seem to remember a thread on the forum with a step-by-step description of the crossover rebuilding process, complete with photos - is that still around?

I know you guys do this work yourselves, but I'm not sure that I want to tackle this project, and certainly not without a good set of instructions. I took a quick look at the Parts Express website, and I'm already overwhelmed.

Can you recommend a repair shop where I can ship the crossovers for the upgrade?

Thanks again.

Face
08-22-2008, 10:09 AM
Where are you located, maybe you can find a local Polkie to help you out.

If you can solder, the crossover on the M7 series isn't difficult. I was a little nervous myself the first time, but here I am now a few months later building much more complex point to point crossovers. http://www.cleanandquiet.com/upload/store/HPD%20Crossover%201.jpg

heiney9
08-22-2008, 10:33 AM
I have a pair of Monitor 7B speakers that I purchased new in 1981. I've used them fairly regularly over the years, except for a few years that they spent in storage.

In reading other posts, I get the impression that capacitor replacement on a
7B of this vintage is considered almost "routine maintenance." Is that really the case? Is there something I should listen for, to know for sure?

Granted, they don't seem to have the same "wow" factor that they had twenty-seven years ago, but I was attributing that to my nearly fifty-year-old ears.

I'm fairly handy, but I don't relish the idea of taking a soldering iron to these speakers.

Is there anything else maintenance wise that needs to be considered? The drivers are working, and everything looks like new.

If there's another post or thread that deals with this issue, please direct me there. I hate to cover the same ground that's been covered elsewhere.

Thanks for your help.

Capacitors have a finite life cycle and do wear out, gradually over time. They have a relative life cycle of anywhere between 10-15 years depending on the quality of the capacitor and if abused can be even shorter. The caps used in mass market products (including that gen Polk) are towards the shorter end. Also, there have been some advances in capacitor materials in the past 27 years that would allow you and manufacturers to economically take advantage of those improvements.

So yes, it will be beneficial if you replace them. It's a very straight forward procedure and while you are in there it's recommended to change the resistor(s) to non-inductive type since they are in the signal path. Mills and Bennic make non-inductive types for about $2-3 each.

If electronics tinkering isn't your thing then it's not necessary unless you are noticing performance issues. It's sort of like giving your car a tune-up; the reward in better sound is well worth the small effort and expense.

It's for you to decide, but ordering online from these companies is easy and the work is minimal if you follow other people suggestions.

www.partsexpress.com

www.madisound.com

Here's the thread I made when I refreshed the x-overs in my Monitor 5B's (very similar to the your 7's)

http://www.polkaudio.com/forums/showthread.php?t=51420&highlight=5b*

Good luck

H9

TomB
08-25-2008, 09:42 AM
Thanks, Face and Heiney 9.

I looked at the crossovers over the weekend, and tried to match up what I found to one of the schematics posted elswhere on the board, but I didn't have much luck. Here is what I found:

(a) Two resistors, labeled: 4.5 ohms 10% 5W and 2.7 ohms 10% 5W.

(b) One big white thing, that must be a capacitor, labeled:
T1
E-0012-1
12K100V
mexico
(I can't see any uF rating anywhere. There's also some brown stuff on the ends, where fluid may have leaked?)

(c) A smaller black thing, probably also a capacitor, but the markings are on the bottom, so I can't read them.

(d) A coil, with no markings.

The schematics all show TWO coils, but only ONE resistor. They also show a "safety guard", but if I have that, I couldn't find it. (I do have a fuse near the binding posts.)

Is this typical? Why doesn't my crossover match up with any of the schematics?

george daniel
08-25-2008, 10:11 AM
Since yours are fused, you should not have a polyswitch,,can you post a picture of the crossover,,almost sounds like you have the crossover of a 7a,,IIRC. Good luck

Face
08-25-2008, 10:24 AM
Don't worry about any of the schematics being a perfect match, there were a few variations of the Monitor 7's over the years. What color is the face plate around the tweeter? How about the tweeter itself?

The big white thing is a 12uf capacitor and the smaller black thing is a 34uf.

If you have a fuse on the back, you don't have a safety guard on the crossover.

TomB
08-25-2008, 11:24 AM
George, give me a day or two, and I can post a picture of the crossover.

Face, I believe I have the Peerless tweeter: black faceplate, v-shaped leads, and black dome with a hole in the middle. The back of the tweeter has a ink-stamped, seven or eight digit number. (Kind of smudged.)

And, I bought these (new) in 1982, rather than 1981, as I posted earlier. The midrange driver has a February, 1982 test date from Polk. I can get the serial numbers, if that would help, but they both start with "7B".

Face
08-25-2008, 11:35 AM
This should be them on the right.

http://a173.ac-images.myspacecdn.com/images01/80/l_6813a37464a217b526228d65dbe26ff4.jpg

george daniel
08-25-2008, 11:43 AM
Face is right on the cap values,, IIRC, when I did mine,,I just pulled the crossovers,identified the components,replaced them, just be sure you have room on the crossover to get them back in,, the caps are much larger then the ones you will be replacing.I know,, I found out the hard way.:o Good luck.

TomB
08-25-2008, 12:10 PM
Face: yep, that looks like them.

George, what does "IIRC" mean?

I'm leaning toward giving this project a try. While I'm not into tinkering for the sake of tinkering, I do want stuff to work right, and it sounds like this needs to be done.

It looks like Sonicraft has several different product lines of capacitors: which one do I use? It doesn't look like the values are exactly right in all of the lines, either.

Finally, if I decide this project is beyond me, do commercial speaker rebuilding outfits do this kind of work? Is there a good one in the Kansas City area that anyone could recommend? I'd like to avoid taking things apart, or shipping the entire speaker, if possible.

Face
08-25-2008, 12:12 PM
IIRC=If I Remember Correctly

As for Sonic Craft, you want the Sonic Cap Gen I's.

george daniel
08-25-2008, 12:12 PM
IIRC-- lets see,, I used to know---oh yeah,,, If I Remenber Correctly:)

TomB
08-28-2008, 01:14 PM
In a Sonicap Gen I, it looks like the closest thing to a 34uF is a 30uF - is that close enough? Or do I put in a 30uF and a 4uF? I did notice on the Parts Express website that they carry a 33uF in some other brands, e.g. Jantzen.

Also, on my existing capacitors, why is the 12uF bigger than the 34uF - are they different kinds/designs?

jon s
08-28-2008, 02:03 PM
different types of caps....

guptonr
08-31-2008, 10:45 PM
I'm going to recap my 7Bs soon too. The schematics show a mylar 12uf and electrolytic 34uf. Do the new caps have to be of the same material or can some of the polypropylene film caps like dayton or jantzen be used?

ben62670
08-31-2008, 11:19 PM
.... or can some of the polypropylene film caps like dayton or jantzen be used?

First welcome to Club Polk.
These are just fine. I prefer the Dayton's of the two. I didn't like the Solen's PE has. 33uf is fine too. Polk used 33-36uf in that XO.
Where in GA are you?
Ben

Disc Jockey
09-01-2008, 12:58 AM
+1 on the Daytons over the Solens, they are smoother than the Solens in the mids

guptonr
09-01-2008, 12:09 PM
Thanks for the welcome and tips on caps. The Daytons sound like a good idea and they worked well in my first recap job I did last week in a pair of HPMs. I'm in Madison, GA which is about 70 miles east of ATL and 25 miles south of Athens.

ben62670
09-01-2008, 03:06 PM
Thanks for the welcome and tips on caps. The Daytons sound like a good idea and they worked well in my first recap job I did last week in a pair of HPMs. I'm in Madison, GA which is about 70 miles east of ATL and 25 miles south of Athens.

I am in Conyers. You are welcome to stop by any time.
Ben

guptonr
09-01-2008, 11:01 PM
Howdy neighbor. We'll have to get together.

ben62670
09-02-2008, 12:27 AM
Yes sir!

TomB
09-02-2008, 03:31 PM
I'll probably go with the Dayton capacitors and the Mills resistors, since Parts Express has the right values on both of those items. And, since it doesn't look like there's a schematic that matches my version of the crossover, I'll just put the new stuff where the old stuff was. (one crossover at a time, as advised!)

Are there any more items to upgrade, "while I'm at it"? I'm thinking mainly of the internal wiring: it's kind of amazing that we get huge speaker cables, but everything still ends up going through that small internal wiring, that looks to be about 14-gauge. (Plus the resistors?)

Thanks again to all.

ben62670
09-02-2008, 03:34 PM
The wire in those is sufficient. The caps, nd resistors are all that are needed;)
Enjoy.
Ben

guptonr
09-07-2008, 12:16 PM
If any of you have any ideas on my proposed cap replacement, I'd love to hear them.

I got my hands on my 7Bís crossovers to see what parts I need. The crossover had a 12uf 100v cap, 34uf 50v cap, a 2.7ohm 5w (10%) resistor and a 4.5ohm 5w (10%) resistor. Like the above poster, my crossover has 2 resistors instead of just one.

These are my proposed replacements:
Dayton DPMC-33 33uf 250v Polypropylene Capacitor
Dayton DPMC-12 12uf 250v Polypropylene Capacitor
Mills 2.5 ohm 12w non-inductive (1%) resistor
Mills 4.5 ohm 12w non-inductive (1%) resistor

I have a couple of questions about them though:
- Is a 33uf cap ok to replace a 34uf?
- Do I need to replace 5w resistors with 5w or will the 12w non-inductive Mills be ok?
- Can I replace a 2.7ohm resistor with 10% tolerance with a 2.5ohm resistor with 1%
-- If thatís not a good idea, is it ok to have the 4.5ohm 12w non-inductive and a 2.7ohm 5w (10%) wire wound?

The reason for the mix and match is that Iím trying to get my parts from one source to cut down on shipping charges. Parts Express doesn't carry a Mills 2.7w or a 4.5w wire wound. The Dayton 2.7w non-inductive resistor is way too big (45mm long).

Face
09-07-2008, 12:20 PM
You'll be fine.

ben62670
09-07-2008, 12:49 PM
Yep. Your good.
Ben

guptonr
09-07-2008, 01:11 PM
thanks guys. I'll order the parts and when I get home next week, I'll comence to solderin'.

ben62670
09-07-2008, 01:17 PM
You can always swing by hear if you want. Won't take but a few to get them done:)
Ben

TomB
09-08-2008, 11:36 AM
Guptonr, where are you ordering your parts from? I thought it looked like Parts Express had about everything, but I hadn't looked that closely. (I'm the "Other Poster" that started this thread.)

Let us know how it goes - heck, I may even send you MY crossovers, after you've had a chance to practice on yours!

guptonr
09-08-2008, 06:21 PM
TomB: I ordered from Parts express. Here's the part #s:

027-430 Dayton DMPC-12 12uF 250V Polypropylene Capacitor
005-2.5 Mills 2.5 Ohm 12W Non-Inductive Resistor
005-4.5 Mills 4.5 Ohm 12W Non-Inductive Resistor
027-441 Dayton DMPC-33 33uF 250V Polypropylene Capacitor

The new caps are a bit bigger, but after a bit of measuring it looks like they will fit ok.

Thanks for starting the thread, it seems our crossovers are exactly alike and don't match any of the schematics.

TomB
09-09-2008, 03:44 PM
Thanks, guptonr.

TomB
09-15-2008, 03:01 PM
Is there an advantage to using a 12W resistor in the 7B crossover, instead of the 5W that was originally installed?

ben62670
09-15-2008, 03:05 PM
Is there an advantage to using a 12W resistor in the 7B crossover, instead of the 5W that was originally installed?

With a 5w resistor resistance will increase with more power applied. Also a 5w will heat up faster and change the value of the resistor.

TomB
09-16-2008, 11:20 AM
Thanks, Ben. Now, as soon as Guptonr gets [U]his[U] upgrade done and posts his report, I'll be ready to proceed.

In reviewing this thread, I noticed that George Daniel suggested an integrated tube amp - any specific recommendations? I'm getting upgrade-itis, now that the days are getting shorter.

george daniel
09-16-2008, 01:31 PM
Me,, I would try a Manley Stingray or Rogue Cronus,,,I can't speak to the Jolida,, but alot of people seem to like them,,good luck.

guptonr
09-16-2008, 10:51 PM
I finished my recapping this evening. I haven't had a chance to place the speakers in a good listening area yet. They're sitting next to my work bench hooked to a Marantz 2250. So far they sound great. The highs seem a little more crisp and detailed and the bass less muddy and punchier (sorry if I didn't use the right audio terms). I'll move them to my basement den, hook them up to a Yamaha CR-2020 and give them a good shakedown.

The installation of the parts couldn't have been easier. Although the new parts are larger than the originals, the leads on the new parts are long enough to make the fit easy. The crossover itself is large enough to accommodate the new parts too and reinstallation of the crossover was no issue. A couple of tips: take the wires off the drivers so you can completely remove the crossover to work on it and make a small diagram of what part goes where because the board doesn't have any labels. I removed all the old parts before putting on any of the new ones because I could install them in the order required to fit the crossover.

The only SNAFUs were self inflicted. When reinstalling the tweeter on the first speaker, I soldered the wires to the terminals but still had them coming out of the woofer hole in the speaker so I had to undo it. On the second speaker, I forgot to label the wires coming off of the crossover so I had to pull the crossover out of the first one to figure out which was which.

It was fairly easy to, even for a complete novice like me. I'll try and get some pics posted tomorrow.

ben62670
09-16-2008, 11:03 PM
Congrats man! I always enjoy the response from those that actually venture into the upgrade!
Ben

guptonr
09-19-2008, 01:12 PM
Here's the pic of the finished 7b crossover with Dayton caps and Mills resistors.

Randall

http://imgcash6.imageshack.us/img187/1847/polk7bxover2ct4.jpg

george daniel
09-19-2008, 01:15 PM
how do they sound? Nice job.

TomB
09-19-2008, 02:26 PM
Looks good, Randall. I'm getting ready to place my order with Parts Express - the same items you listed in your earlier post, since our crossovers are identical. It doesn't look like the larger sized capacitors will be a problem to fit back into the speakers.

Did you have any trouble with those little plastic tab thingies? Don't you have to release those to get to the underside of the board? I was afraid the plastic might be brittle after all these years.

One more question for the experts on the forum...

How do you solder?

Seriously.

I can do all manner of home improvement and culinary projects, but I've never soldered electronic components before. I've done a little bit of reading, but it wasn't very helpful. The Parts Express website has some information on the basics that was as good as anything else I've been able to find.

We have an 80 watt soldering iron that my wife uses for stained glass, and one of the ancient "gun" style irons that's about 120 watts. Those may be too big - the websites say that a 30-40 watt iron is ideal for this kind of stuff. If I need to buy one, I'll probably just order it from Parts Express, along with the other components.

What else do I need, besides rosin-core solder? The case with the old soldering gun has a pointy aluminum tool that looks like it would be handy for holding leads, etc., and for cleaning old solder out of the holes in the board.

From what I've read so far, "un-soldering" is harder than the actual soldering. Is solder wick really helpful to get rid of old solder?

Thanks again for the report, Randall. It's helpful to have someone else with my exact speaker who has done this project. I'm gonna print out your picture to use as an example!

ben62670
09-19-2008, 02:32 PM
You can use the hot irons no problem here. Don't worry about removing the old solder. Go to Rat Shack and get some Silver bearing solder that is on a roll. Not the stuff in a tube. The stuff is easy to work with, and makes a nice clean joint. Use a moist sponge to clean the iron.
Ben

jon s
09-19-2008, 02:35 PM
get a Radio Shack 45-watt desoldering iron (http://www.radioshack.com/product/index.jsp?productId=2062731&cp=&sr=1&kw=soldering+iron&origkw=soldering+iron&parentPage=search) for $11. Makes life a lot easier.

Get any decent 25-30 watt soldering iron and u will be good to go... for best conductivity, some people recommend silver solder, but they are a wee bit harder to use...

ben62670
09-19-2008, 02:45 PM
get a Radio Shack 45-watt desoldering iron (http://www.radioshack.com/product/index.jsp?productId=2062731&cp=&sr=1&kw=soldering+iron&origkw=soldering+iron&parentPage=search) for $11. Makes life a lot easier.

Get any decent 25-30 watt soldering iron and u will be good to go... for best conductivity, some people recommend silver solder, but they are a wee bit harder to use...

Not the Silver solder I recommened. It's cheap, melts at a low temp, and bonds very well. Also if he isn't going to be doing much soldering in the future he will be fine with the 80watt as long as it has a clean tip.

TomB
09-19-2008, 03:17 PM
Thanks, Ben and Jon.

I'm really not close to a Radio Shack, if you can imagine such a thing. Parts Express has this:

http://www.partsexpress.com/pe/showdetl.cfm?&Partnumber=093-586

Is that the right silver solder? If so, I'll order some.

If Radio Shack has something equally good that's cheaper, I can probably get there.

As you mentioned, I'm probably not going to be doing a lot of soldering, so I'd like to keep my investment down - although I'll use about any excuse to get another tool!

schwarcw
09-19-2008, 03:24 PM
Tom, the WBT is good stuff! I personally like the Cardas, but I doubt you would see much difference in these soldering applications (PCB connections).

Randall, nice work! I'm contemplating redoing my Monitor 7's. I'll comtemplate some more.:cool:

ben62670
09-19-2008, 03:48 PM
...although I'll use about any excuse to get another tool!

Sounds like me:) I have a ton of tools I used once:D
The Rat Shack stuff is $6 for 1.5oz, but after gas and time You might be better off with the WBT.

TomB
09-19-2008, 04:28 PM
Yeah, Ben, one of my recent purchases was a tool to adjust the headlight aim on late-model Fords - it's like a 4.3mm (or some other odda** size) socket. I used it once, and it worked great! Let me know if anyone needs to borrow it: it's hanging in my garage.

I found the Radio Shack stuff on their website: is it similar to the WBT, even though the WBT isn't described as "bearing" solder?

guptonr
09-19-2008, 08:46 PM
Tom,

Those plastic things were no problem. with your fingers or needle nose pliers, just push in the "barb" and they will pop right out of the hole. I'm really not one to give soldering tips because I'm such a noob at it. These other guys will steer you straight. I did a little research on the net and found lots of "how to's." I also practiced a couple of times just joining pieces of wire together. A couple of tips for this task: I labeled the holes on the underside of the board with a sharpie to make sure I put lead into the correct hole; I didn't cut of any of the leads from the new parts until after I had soldered them in place. It was pretty easy to poke the long leads through the holes and bend them into place before soldering. Then I just snipped of the excess.

Randall

ben62670
09-19-2008, 09:12 PM
....I also practiced a couple of times just joining pieces of wire together. A couple of tips for this task: I labeled the holes on the underside of the board with a sharpie to make sure I put lead into the correct hole; I didn't cut of any of the leads from the new parts until after I had soldered them in place. It was pretty easy to poke the long leads through the holes and bend them into place before soldering. Then I just snipped of the excess.

Randall

Excellent advice!

rolling18
10-15-2008, 01:43 AM
If any of you have any ideas on my proposed cap replacement, I'd love to hear them.

I got my hands on my 7Bís crossovers to see what parts I need. The crossover had a 12uf 100v cap, 34uf 50v cap, a 2.7ohm 5w (10%) resistor and a 4.5ohm 5w (10%) resistor. Like the above poster, my crossover has 2 resistors instead of just one.

These are my proposed replacements:
Dayton DPMC-33 33uf 250v Polypropylene Capacitor
Dayton DPMC-12 12uf 250v Polypropylene Capacitor
Mills 2.5 ohm 12w non-inductive (1%) resistor
Mills 4.5 ohm 12w non-inductive (1%) resistor

I have a couple of questions about them though:
- Is a 33uf cap ok to replace a 34uf?
- Do I need to replace 5w resistors with 5w or will the 12w non-inductive Mills be ok?
- Can I replace a 2.7ohm resistor with 10% tolerance with a 2.5ohm resistor with 1%
-- If thatís not a good idea, is it ok to have the 4.5ohm 12w non-inductive and a 2.7ohm 5w (10%) wire wound?

The reason for the mix and match is that Iím trying to get my parts from one source to cut down on shipping charges. Parts Express doesn't carry a Mills 2.7w or a 4.5w wire wound. The Dayton 2.7w non-inductive resistor is way too big (45mm long).

Hello!
would this setup work great on my "monitor 7"? (unknown year)

i inherited mine a few years ago, and I could not bring myself to pawn them for $$$. I did not know how great they were until i got some good stereo equipment.

I had no idea they could sound even better, but i learned from this forum its possible. thankyou!!

ben62670
10-15-2008, 01:47 AM
Sure can. Monitor 7's are a great speaker even by todays standards. They would be an easy upgrade, and well worth the investment. I have done about 15-20 XO upgrades, and it is money well spent.
BTW welcome to club Polk.
Ben

TomB
10-21-2008, 02:13 PM
Randall, if you're around, I sent you a private message with another question about your upgrade.

Tom

TomB
11-23-2008, 08:47 PM
I've had the parts sitting around for a couple of months now, and I finally got the nerve to rebuild the crossovers on my 7Bs this afternoon. With all of the help and advice I received from you folks, the project was surprisingly easy!

As Randall mentioned, it a little trouble to contour the leads on the new resistors and capacitors, since they're considerably larger than the old ones. (My biggest worry was having too much extra length and "play" in the leads, and end up shorting out something, if the leads contacted each other. However, everything "firmed up" nicely, once the soldering was done.)

The second one was MUCH easier than the first - I just wish I had some more speakers to work on! (These 7Bs are the only speakers I've ever owned - I purchased them new in 1982.)

I've only listened briefly, to make sure everything worked, but the sound is crisper, with tighter bass and more precise imaging. I'm looking forward to more listening this winter.

One other thing I did: while I had an order in to Parts Express, I got some DeOxit. For quite some time, I've had a noisy volume control on my ancient Harman Kardon receiver, so I pulled the cover and gave all the pots a GOOD cleaning. Not only are the controls quieter, I think the sound is better overall. (I guess all those controls are in the signal path, right?)

I consicered giving the drivers and radiators on the 7Bs the Mortite treatment, as described in another thread, but I really didn't see the need: I gently pushed the passive radiator in, and the midrange driver pushed out quite nicely, and just stayed there, until I released the PR. Sounds like the seals are still pretty tight, so I decided not to mess with them.

Thanks again for all of your help.

guptonr
11-23-2008, 09:27 PM
Congrats on the job well done. I was thinking of giving my speakers the Mortite treatment too. When I get home, I'll try the passivie radiator test.

TomB
11-23-2008, 09:40 PM
Randall, I printed out the picture of your completed crossovers, and had it right in front of me for reference - and inspiration! Thanks.