Please review my Monitor 5 recap plans

KenAnderson
KenAnderson Posts: 6
in Vintage Speakers
I obtained my Monitor 5s free, and they don't sound as good as I'd like, so it's recap time. I've already replaced the external fuses, and that helped big time.

I have no soldering experience, and nowhere near the electronics knowledge that I'd like to have, but this really doesn't look too hard. To practise my soldering skills, I unsoldered tiny resistors and caps in a radio I picked up at the dump, and then soldered them back in. I'm feeling confident about being able to do the larger components that I think I need for this project.

I've read a bunch of posts in this forum, and think I know what I need to do, but I'd really appreciate it if one or more of you would just have a look at my plans and let me know if I'm good to go, or if I need to make changes.

I've attached a pic of the crossover below.

As near as I can tell, I have the following parts.
  • 12uf at 50vac electrolytic capacitor
  • 34uf at 50vac electrolytic capacitor
  • 6.2 ohm resistor at 5w
  • 2.7 ohm resistor at 5w

I plan to replace these with one of the following configurations. One config is considerably more expensive than the other.
Expensive
  • Sonicraft GEN I 12uf Capacitor, from Sonic Craft, 28.46 USD each
  • Sonicap Gen I 34 uF 200VDC, rom Sonic Craft, 62.01 USD each
  • Mills Resistor 6.2 ohm 5 watt MRA-5, from Sonic Craft, 4.60 USD each
  • Vishay Mills Resistor 2.7 ohm 5 watt MRA-5, from Sonic Craft, 3.95 USD each

Sonic Craft shipping 24.12 USD

Total price for two of each component plus shipping to Victoria, B.C., 295.47 CAD!

Cheaper
  • Clarity PX 12uF 250VDC, from Meniscus, 9.40 USD each
  • Jantzen Audio 33uF 400V Crosscap Capacitor, from Parts Express, 13.54 USD each
  • Mills Resistor 6.2 ohm 5 watt MRA-5, from Sonic Craft, 4.60 USD each
  • Vishay Mills Resistor 2.7 ohm 5 watt MRA-5, from Sonic Craft, 3.95 USD each

Meniscus shipping 12.25 USD
Parts Express shipping 31.31 USD
Sonic Craft shipping 14.93 USD
Sonic Craft handling 10.00 USD

Total price for two of each component plus shipping and handling to Victoria, B.C., 174.06 CAD.

I think I'll go the cheaper route, and save myself $125 CAD.

I understand that I should also get replacement standoffs, in case the existing ones don't survive my work. Where do I go to get these?

And, lastly, the existing caps are rated at 50VAC. Replacements are VDC caps. Will that cause me any problems? If "yes", what do I do to deal with those problems.

Thanks,
-Ken

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Comments

  • VR3
    VR3 Posts: 28,639
    Sounds luge a solid plan

    Rock N roll
    - Not Tom ::::::: Any system can play Diana Krall. Only the best can play Limp Bizkit.
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  • Gardenstater
    Gardenstater Posts: 4,459
    edited February 2020
    I have been under the impression (If I'm mistaken someone correct this) that if you spec a cap at DC of twice the AC value you're OK. So for those 50VAC caps you would go 100VDC or greater.

    Another thing is that it is advisable to go for the 12W resistors, even though the existing ones are only 5W, because you will get less heat intensity produced and you will get less thermal noise in the resistor as a result.

    Don't know about the standoffs but I understand that you want to keep them nylon. I may need to get longer ones for my own rebuild on my 7B crossovers, especially if I need to mount the large caps underneath the board. If I find out where to get I'll let you know.

    Congratulations on free Monitor 5s. Since you mention that they don't sound as good as you would like you should do the push test on the midbass drivers to see if there are any scraping sounds where you will feel/hear the voice coils scraping against the magnet or pole piece. That would be a negative for performance to say the least. If they are good you want to put some adhesive around the magnet assemblies to keep them that way.
    George / NJ

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  • pitdogg2
    pitdogg2 Posts: 25,437
    I'd step up to 12 watt resistors. The stand offs should survive just fine. A small pair of needle nosed pliers are a god send for those. Squeeze in the catch and pull up gently on each. The biggest factor is the new caps are bigger. I'd shy away from the 400v caps they more than likely will be a monster. Check sizes on them carefully.

    If you're in Canada try
    https://www.partsconnexion.com/
    I order from them often.
    Another problem we run into on the older speakers with fuses is corrosion where the wires connect to the fuse holder. if you want to keep the fuses you may need to run new wire to that connection point.

    some people remove the fuses all together and just run direct wire to the crossover board.
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  • KenAnderson
    KenAnderson Posts: 6
    Thanks for the feedback, @Gardenstater.
    ...if you spec a cap at DC of twice the AC value you're OK. So for those 50VAC caps you would go 100VDC or greater.
    OK, so it looks like I'm good to go on that.
    ...it is advisable to go for the 12W resistors, even though the existing ones are only 5W...
    Ok, those exist.
    • Clarity PX 12uF 250VDC, from Meniscus, 9.40 USD each
    • Jantzen Audio 33uF 400V Crosscap Capacitor, from Parts Express, 13.54 USD each
    • Mills Resistor 6.2 ohm 12 watt MRA-12, from Sonic Craft, 7.34 USD each
    • Vishay Mills Resistor 2.7 ohm 12 watt MRA-12, from Sonic Craft, 5.50 USD each
    ...you should do the push test on the midbass drivers ... put some adhesive around the magnet assemblies to keep them that way ...
    I'll look these procedures up.

    Thanks for the advice.
    -Ken

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  • F1nut
    F1nut Posts: 50,542
    Are these keepers? If so, you're much better off going with Sonicap in the exact values. I strongly believe in using the exact values.

    If not keepers at least use a Clarity CSA for the tweeter.

    BTW, that 400V cap is going to be very large.
    Political Correctness'.........defined

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  • slow_polk7
    slow_polk7 Posts: 34
    KenAnderson wrote: »
    I've already replaced the external fuses, and that helped big time.

    Is this truly possible?
    I would like to know as I have original, untouched Monitor 5s.

    It "seems" that the presence of an intact fuse would be a go/no-go situation, but maybe I'm mistaken.
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  • pitdogg2
    pitdogg2 Posts: 25,437
    slow_polk7 wrote: »
    KenAnderson wrote: »
    I've already replaced the external fuses, and that helped big time.

    Is this truly possible?
    I would like to know as I have original, untouched Monitor 5s.

    It "seems" that the presence of an intact fuse would be a go/no-go situation, but maybe I'm mistaken.

    knocked off corrosion in the replacement of the fuse. If some fuses sit for extended period some corrosion forms on the fuse/holder. We have seen where there was a good fuse but no tweeter. We asked that the person use a brush or green scrubby to clean fuse and holder and back comes the tweeter.
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  • slow_polk7
    slow_polk7 Posts: 34
    Very interesting!
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  • michaeljhsda2
    michaeljhsda2 Posts: 2,182
    I used white vinegar (not apple cider vinegar) to remove battery corrosion in a remote control that I thought was ruined but it works great. Not sure how effective it would be in your case.
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  • KenAnderson
    KenAnderson Posts: 6
    slow_polk7 wrote: »
    KenAnderson wrote: »
    I've already replaced the external fuses, and that helped big time.

    Is this truly possible?
    I would like to know as I have original, untouched Monitor 5s.

    It "seems" that the presence of an intact fuse would be a go/no-go situation, but maybe I'm mistaken.
    @slow_polk7, the fuses I replaced were burnt out. I guess somebody had cranked things up a bit.

    -Ken

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