Mission 720 crossover rebuild guidance

Markoneswift

Quartz locked n ready to rock
Hi all,

I've had these Mission 720 sitting around for quite a while waiting to get their surrounds done. I finally pulled the woofers and got with it this weekend and then I looked at the crossovers.

These circuits are some of the more complex crossovers I've seen so far and I suspect finding appropriate replacement parts is going to be. I will post details of all the components when I'm home later....
 
Found this thread on reworking/repair of a pair of Mission 720s.If you have the same caps as shown in the thread instantly replace them.https://www.vintage-radio.net/forum/showthread.php?t=61264 I will see if I can find anything on the crossover. Have a pair of 737Rs.

Thanks for the link, yep I have those Elcap axial caps all over my boards. Finding alternatives is going to be tricky, especially here in NZ. One ceramic resistor looks like toasted marshallow so someone has either cranked these or had a defective amp (most likely the latter as the other x over is very clean).
 
What caps CAN you get in NZ? Will Parts Express or Erse Audio deliver to you there?

Lee.
 
What caps CAN you get in NZ? Will Parts Express or Erse Audio deliver to you there?

Lee.

Good question mate. The answer is yes, most suppliers will ship to me but it can get expensive if the order value is not high. For example I recently looked at getting a few components from Mouser, totalling about $28, but decided against it with $60 shipping on top !!

I will get all the cap values listed out first and see what I can find here - axial caps are not easy to find but I may be able to fit radial in most instances if the legs are long enough...
 
Looking at the schematic below :

Mission 720.JPG

You would probably need the following components :

Mission 720 crossover caps - Erse Audio

Tweeter
6uf MET25-05-6.00/PB 1.76
10uf MET25-05-10.0/PB 2.65

Midrange
60uf: 50uf ANP10C-05-50.0/PB 0.88 and 10uf MET25-05-10.0/PB 2.65
16uf ANP10C-05-16.0/PB 0.56

Woofer
41uf - 40uf ANP10C-05-40.0/PB 0.78

Total (per speaker) 9.28
Grand Total 18.56

The total comes to just under $20 US before shipping. I went with film caps on the tweeter circuit, and the 60uF cap in the midrange circuit is made up of a 50uF electrolytic and a 10uF film. The woofer cap, I used a 40uF, I doubt if you would notice the difference compared to the 41uF that Mission used. If you really really had to have the value Mission used, you could make this up from a 16uF and a 25uF just as they did.

This order comes below the $20 minimum that Erse Audio has. I might have to order some caps for a KEF 103.2 crossover that someone else was asking about. If you're not in too much hurry for these, I could add them to my next order, and investigate the cost of shipping them to NZ from the USA?

Lee.
 
Looking at the schematic below :

View attachment 1192801

You would probably need the following components :

Mission 720 crossover caps - Erse Audio

Tweeter
6uf MET25-05-6.00/PB 1.76
10uf MET25-05-10.0/PB 2.65

Midrange
60uf: 50uf ANP10C-05-50.0/PB 0.88 and 10uf MET25-05-10.0/PB 2.65
16uf ANP10C-05-16.0/PB 0.56

Woofer
41uf - 40uf ANP10C-05-40.0/PB 0.78

Total (per speaker) 9.28
Grand Total 18.56

The total comes to just under $20 US before shipping. I went with film caps on the tweeter circuit, and the 60uF cap in the midrange circuit is made up of a 50uF electrolytic and a 10uF film. The woofer cap, I used a 40uF, I doubt if you would notice the difference compared to the 41uF that Mission used. If you really really had to have the value Mission used, you could make this up from a 16uF and a 25uF just as they did.

This order comes below the $20 minimum that Erse Audio has. I might have to order some caps for a KEF 103.2 crossover that someone else was asking about. If you're not in too much hurry for these, I could add them to my next order, and investigate the cost of shipping them to NZ from the USA?

Lee.

Hi Lee,

Looks good to me mate - so all the proposed parts will more or less fit onto the standard board with a few tweaks ? Any thoughts on where it's worthwhile replacing the original inductors with air core types ?
Thanks for the help so far, looks like I found the right guy for the job :) I'm not in a big hurry so yes if you could tag them onto your next purchases that would be awesome. I've had a few packages sent from the US to NZ for my Akai R2R from fellow AKer Matt, so that would work for me. I can simply Paypal you the funds.

Let me know if that's all good with you and in the meanwhile I will get the surrounds for the mids ordered and installed.

Cheers.
 
Well, if you look at some of my KEF crossover threads, you'll see that some of the larger film caps don't quite fit. But you can always play with the lead length, and use hot melt glue to hold them in place.

As for the inductors, no, I wouldn't replace those iron cored ones with air cored. The DC resistance will be higher and may upset the crossover design.

Lee.
 
Well, if you look at some of my KEF crossover threads, you'll see that some of the larger film caps don't quite fit. But you can always play with the lead length, and use hot melt glue to hold them in place.

As for the inductors, no, I wouldn't replace those iron cored ones with air cored. The DC resistance will be higher and may upset the crossover design.

Lee.

Great, sounds good thanks Lee. Let me know when you're ordering in the parts and we can sort out payment etc.
 
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