[moe]

I got some speakers from my Dad recently.  They're CS-77s from the early 70's.  From what I've read, they're not top-of-the line, but they're pretty nice.
I remember them fondly from my childhood.  I didn't use them much for a few months while I tried to figure out what to do with them.  I finally decided to keep them, cleaned them up, had the tweeters re-foamed and turned 'em on.
One sounded normal (pretty nice to me) and the other had some issues (really quiet).
I changed wires and terminals to verify the speaker and it was....
I got out the voltmeter and found one the of caps on the crossover basically shorted (1 ohm).
The individual speakers all show a resistance of 6.5- 7.5 ohms - so I assume they're ok.

My questions:
Is it still possible to replace this capacitor with one of the same size and shape?  I'd rather not have to change the crossover board configuration.

Should I replace all of the capacitors - given the age of this crossover?

If yes, then I likely should replace all of the capacitors for the other speaker too?

I think I've got the schematic pretty close, but I'm not an expert - RSW=rotary switch - which can select between settings Decrease, Normal and Increase for the HIGH and MID Ranges.

Any advice is welcome.

Moe

[richidoo]

Welcome to AudioCircle.

That's a nice looking crossover.

In order to properly measure a capacitor you have to lift one of it's leads from the circuit board so it is isolated from the rest of the crossover components. If you measure resistance while it is installed then other connected components may affect your readings.

The caps are probably bipolar electrolytic type. They can be replaced with similar parts. They should have voltage rating high enough for the amplifier signal, typically they are 100V or higher.  They could also be replaced with film caps, which usually have better sound quality and will last forever, but could change the sound a small degree from the original voicing. Generally film caps are the standard now.

The number printed on the caps is the capacitance value.

[PMAT]

Great advice, remember though that film capacitors probably won't fit on that board because they are huge compared to electrolytic caps. I would use the same electrolytic capacitors they will last for 20 years. As long as the voltage is the same or higher you'll be fine but don't change the value (ohms).

[srb]

As long as the voltage is the same or higher you'll be fine but don't change the value (ohms).

ummm ..... µF (microfarads)  ?

[moe]

Thanks for your reply.

"In order to properly measure a capacitor you have to lift one of it's leads from the circuit board so it is isolated from the rest of the crossover components. If you measure resistance while it is installed then other connected components may affect your readings."

Thanks.  I've forgotten too much it seems.

"The caps are probably bipolar electrolytic type. They can be replaced with similar parts. They should have voltage rating high enough for the amplifier signal, typically they are 100V or higher."

If the old amp was rated at 40W and the new one is 100W should I significantly raise the voltage?  Is there a voltage peak - where a higher voltage rating won't matter any more?

Thanks for your help with this.

moe

[moe]

I pulled all of the capacitors out of the board today.  Here's what they were stamped with vs what the actual readings were:

50µF - actually 67.7µF
30µF - actually 44µF
5µF   - actually 7µF
3µF   - actually 4.11µF
0.5µF- actually 0.639µF

Do these numbers indicate that the caps were bad/going bad?

Thanks,
Moe

[Jeff]

Moe,

Welcome to my forum

Is it still possible to replace this capacitor with one of the same size and shape?

There are many sizes and shapes available, but just about every cap out there has its dimensions listed somewhere.  The main importance here is value, voltage, and general sonic character.

I'd rather not have to change the crossover board configuration.

No problem.

Should I replace all of the capacitors - given the age of this crossover?

Yes.

If yes, then I likely should replace all of the capacitors for the other speaker too?

Yes.  Even if you were only replacing one cap in one speaker, you should replace the one in the same position in the other speaker.  Otherwise, the two speakers are likely to sound different.

typically they are 100V or higher.

This is not typical.  A "true" 50V or greater is more common.  The CS-77a is rated to handle a max of 65W, and it is a 8 Ohm speaker.  Or, 22.8V, so 50V should allow enough power to catch the drivers on fire   I'd rather lose a cheap cap than one of these old drivers

They could also be replaced with film caps, which usually have better sound quality and will last forever, but could change the sound a small degree from the original voicing. Generally film caps are the standard now.

I agree if the right film caps are selected.  When the wrong ones are selected, many have found they prefer electrolytics.  I would not say film is the standard now, but it should be.  BTW, film will likely outlive us, but they will not live forever.  Some will be lucky to make 30-40years.

50µF - actually 67.7µF
30µF - actually 44µF
5µF   - actually 7µF
3µF   - actually 4.11µF
0.5µF- actually 0.639µF
Do these numbers indicate that the caps were bad/going bad?

It is hard to say what is going on here.  First, how accurate are your measurements.  Second, none appear to be shorted.  So third, you could measure ESR, which is likely quite high.  However, I can tell you they are junk.  I can also tell you that any design that uses electrolytics is generally fine in you get within 5-10% of the target value.  None the less, I like to see 1% pairs matching R to L.  It sounds to me as if you are primarily focused on repair/maintenance, but could be swayed towards a small amount of improved performance if it were "big bang for the buck"?  My recommendation:

http://www.soniccraft.com/product_info.php/mundorf-cap-plain-47uf-70vdc-50vac-p-4069
http://www.soniccraft.com/product_info.php/mundorf-cap-plain-33uf-70vdc-50vac-p-4078
http://www.soniccraft.com/product_info.php/mundorf-cap-plain-47uf-70vdc-50vac-p-4068
http://www.soniccraft.com/product_info.php/kimber-kap-30uf-200vdc-p-4651
http://www.soniccraft.com/product_info.php/gen-ii-sonicap-047-uf-200vdc-p-380

If you need solder, you will really like this: http://www.soniccraft.com/product_info.php/cardas-solder-qe-24ft-p-521

[moe]

Jeff-
Thanks for your knowledgeable help with my questions.  When things slow down again, I'll be placing an order.
Moe

[moe]

Jeff,
Thanks for all of your recommendations on the capacitors.  I noted happily that most of them have very similar dimensions, so I won't have to butcher anything to get them to fit.

A few more questions:
1) Do I need to glue the caps to the circuit board?  The old ones had some sort of sticky substance holding them down.
2) With regard to your question to the possibility of the capacitance measurements being off - I used a Fluke meter set to measure capacitance, so I can only assume it measured true.  The meter is used on a weekly basis for regular field measurements.  With that in mind, should I be worried that I have a bad inductor hiding on the board?
3) Do inductors go "bad"?  Would a bad cap mess up the corresponding inductor?

Thanks again for your response.
Moe

[Jeff]

1) No, not any of the caps listed above, but a dab of 100% pure silicone will not hurt either.
2&3) No, not really.

[moe]

I replaced all five caps today.  They didn't seem to make much difference.  The speaker is still putting out a relatively muted sound when compared to the other one.

I'm open to other recommendations for getting it back to normal.

[Jeff]

Moe,

Whether the caps were the problem or not, you needed to replace them.  Once you resolve your other issues, you will find them very pleasant as compared to the original.  So, lets find your problem.  If you have not already, switch the XOs from one speaker to the other.  See if the problem follows the XO.  If it does not, listen to see if the problem is in just one or two drivers, or all the drivers in that speaker.  If you are not sure, try disconnecting "one" driver at a time in both speakers.  Compare, and report back.