Monitor 7B Capacitor Replacement?

TomB

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

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

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 . Good luck,have fun and enjoy.

zingo

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

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

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

TomB wrote: »

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

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

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

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

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

This should be them on the right.

george daniel

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

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

IIRC=If I Remember Correctly

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

george daniel

IIRC-- lets see,, I used to know---oh yeah,,, If I Remenber Correctly:)

TomB

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

different types of caps....

guptonr

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

guptonr wrote: »

.... 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

+1 on the Daytons over the Solens, they are smoother than the Solens in the mids

guptonr

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

guptonr wrote: »

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

Howdy neighbor. We'll have to get together.

ben62670

Yes sir!

TomB

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

The wire in those is sufficient. The caps, nd resistors are all that are needed;)
Enjoy.
Ben

guptonr

If any of you have any ideas on my proposed cap replacement, I'd love to hear them.

I got my hands on my 7B’s 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 that’s 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 I’m 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

You'll be fine.

ben62670

Yep. Your good.
Ben

guptonr

thanks guys. I'll order the parts and when I get home next week, I'll comence to solderin'.