Monitor 7B Capacitor Replacement?

ben62670

You can always swing by hear if you want. Won't take but a few to get them done:)
Ben

TomB

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

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

Thanks, guptonr.

TomB

Is there an advantage to using a 12W resistor in the 7B crossover, instead of the 5W that was originally installed?

ben62670

TomB wrote: »

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

Thanks, Ben. Now, as soon as Guptonr gets his 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

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

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

Congrats man! I always enjoy the response from those that actually venture into the upgrade!
Ben

guptonr

Here's the pic of the finished 7b crossover with Dayton caps and Mills resistors.

Randall

george daniel

how do they sound? Nice job.

TomB

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

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

get a Radio Shack 45-watt desoldering iron 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

jon s wrote: »

get a Radio Shack 45-watt desoldering iron 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

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

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

TomB wrote: »

...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

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

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

guptonr wrote: »

....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

guptonr wrote: »

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).

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

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

Randall, if you're around, I sent you a private message with another question about your upgrade.

Tom

TomB

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

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

Randall, I printed out the picture of your completed crossovers, and had it right in front of me for reference - and inspiration! Thanks.