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Selecting cap for an amplifier rebuild


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One of my old solid states amps is failing (failed) and I suspect, based on the failure mode, it might be dried out electrolytic caps. There's only 7 electrolytics per channel so cost is not a serious concern tho size is.

I can find exactly what I need on mouser.com (is there someplace better to go), but the ripple current spec has thrown me. I'm assuming this is important. Al things being equal, should I choose a cap with the highest or lowest ripple current spec?

Example on what I'm looking for 220, and 100uf 100V polarized electrolytic 20 and 10 uf NP 10V

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I'll wait for more knowledgeable people to chime in but I can tell you mouser is a good source. Another source for audio caps is handmade electronics https://www.hndme.com/productcart/pc/viewCat.asp

Nichicon has a line of caps that are specifically for audio. When I recapped my MAC4100 I used the best Nichicons wherever possible along with Elna Silmic and Panasonic. Here's an audio grade 100/100 http://www.mouser.com/ProductDetail/Nichicon/UFG2A101MHM/?qs=sGAEpiMZZMtZ1n0r9vR22e0BBN1kF1oimcIJkEfPtV0%3d

As you probably know, it's not a bad idea to go up a step in voltage.

If you can't find "audio grade" in the size you need, go with a brand name and a 105 C temp rating or better.

For lower values (10uF and under) you "may" be able to use film caps and these are generally considered to be preferable. Here's a 10uF Panasonic http://www.mouser.com/ProductDetail/Panasonic/ECQ-E2106KF/?qs=sGAEpiMZZMv1cc3ydrPrFxjzI7V0kgrk68MiUidSptQ%3d

Here is a link to Nichicon. Scroll down to the bottom to see the audio caps. http://www.nichicon.co.jp/english/products/alm_mini/pict_f.htm

They also have caps specifically for switching power supplies (the HE and HW line). If your PS is not the switching type, regular caps are fine.

Hope this helps.

-Kent

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It might help if I mentioned the Amplifier is a Heathkit AA-1800. These were based on the Leach Superamp design. Only the 10 uf caps are actually in the audio path. One is on the input, the other in the feedback circuit. The remainder are in the power rails. There is a single ceramic cap and a single film cap as well that I'll likely leave.

I own two of these puppies and the one needing attention is one I procured off eBay and has always been problematic. There are less than a dozen 4 watt carbon resistors per channel. Base on how the leads were formed, their age and the rather shoddy job of soldering, I'm likely to replace them as well.

The second amp is one I build while in the Navy circa early 80's and has been relatively trouble free except for a couple of careless accidents. I will, as a preventative measure, recap it as well.

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I was able to find a Nichicon cap for every value I was looking for. Dimensions won't be exact but they are close enough they will work. I've also ordered metal film resistors to replace the 2 and 3 watt carbon resistors. The smaller resistors are already precision (5%) and I'm leaving them alone. The resistors I've ordered are 5% and will replace 20% parts. Given the low cost, I couldn't justify not spending a few more pennies for the better parts.

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I was able to find a Nichicon cap for every value I was looking for. Dimensions won't be exact but they are close enough they will work. I've also ordered metal film resistors to replace the 2 and 3 watt carbon resistors. The smaller resistors are already precision (5%) and I'm leaving them alone. The resistors I've ordered are 5% and will replace 20% parts. Given the low cost, I couldn't justify not spending a few more pennies for the better parts.

Good news! Please keep us posted (with photos if possible). The Heathkit AA-1800 was one of the amps I was looking for when I decided to quit using a receiver and go back to separates. Nice amp! I never found one but I'm happy with my Adcom 555/II.

A potential issue with Heathkit stuff is that you may get a kit version, and the builder may have been a chimp. I think your plan of re-capping and re-sistoring :lol: is a good one. IF it was kit built you can do some QC but even if factory-built those caps are getting long in the tooth and 20% carbon resistors aren't the most desirable. Good luck!

-Kent

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First channel is done, and the original builder was definitely a chimp. They'd have horribly failed the milspec soldering course I went thru a few decades ago. It was a pleasant surprise to discover the old, original caps are Nichicon.

How do I post photos?

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How do I post photos?

Under the reply area look for "More reply options". On that page there will be a "browse" button to select a photo from your hard drive. Then be sure to click "Attach this file"

Optimal size for photos seems to be about 100 or so KB and no more than about 10 or 12 inches wide.

Upload one at a time.

-Kent

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Something I want to clarify. I did not take on this project for some pie in the sky reason hoping new exotic caps would enable my system to project rainbows or holographically project unicorns. It was simply to restore one amp to functionality and hopefully extend the life of the second amp. I am happy to report my guess of a failed cap being the problem was indeed the issue, and replacing all of the caps fully restored the unit to usefulness. Total cost of the project was under $60 for both amplifiers. That includes all of the caps except the power supply caps plus all of the 2 and 3 watt 20% resistors being replaced with 5%.

What was not anticipated was the very obvious improvement in sonic performance. Difficult to impossible to describe the change. But at one point, I swore I could hear the pianist pounding the keys. Norah Jones, who in the past, has been a bit severe, we can now hear the subharmonics in her voice, I'd swear I could hear her breath. Overall, improved clarity, dynamics, sound stage. More small details that weren't there previously.

So in a nutshell. You do not have to use insanely priced exotic caps willed with fairy dust when replacing 40 year old electrolytic caps. Just choose wisely and do it.

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So in a nutshell. You do not have to use insanely priced exotic caps willed with fairy dust when replacing 40 year old electrolytic caps. Just choose wisely and do it.

Good point. And nice job. I just hope those photos don't show the surface you actually worked on! Looks like my quarter-sawn oak dining table ;)

For those interested in such things, here's a thread on recapping the MAC4100 receiver:

http://www.audiokarma.org/forums/showthread.php?t=176380

I hijacked it around post #65 but all the research was done by Whaleman and he provided a nice shopping list.

It went smoothly but there were some bumps in the road. The 4100 had a few changes over the years that may have been addressed in service bulletins and I did identify (with the help of John O'Hanlon) one cap that had a dangerously low voltage rating. And I did take it to an authorized Mac tech after my work so he could check it over.

I did not replace the carbon resistors but I think you made a wise choice there.

All in all a fun and worthwhile project.

-Kent

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What drove me to replace the 2 and 3 watt resistors was how the original builder formed (bent) the leads. For all the world, it appeared they simply bent the lead with no regard to damaging the resistor body. I've seen far to many resistors and diodes damaged doing this. They work, sort of, but not typically well. I chose to use 5% instead of 20% resistors due to cost. They are so cheap today it didn't make sense not to use them.

After the rebuild, I reset bias and offset , and what I saw surprised me. Previously, bias was a goal more than a real setting, and offset would drift typically around 10mv. Now, bias is very stable (35mv) and offset can be set within .1mv of zero and is stable.

Mouser was good. I did have to call because I was having problems finding the 10mv 10V caps and the rep pointed me quickly to the Nichicon audio grade caps.

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  • 3 weeks later...

Something I want to clarify. I did not take on this project for some pie in the sky reason hoping new exotic caps would enable my system to project rainbows or holographically project unicorns. It was simply to restore one amp to functionality and hopefully extend the life of the second amp. I am happy to report my guess of a failed cap being the problem was indeed the issue, and replacing all of the caps fully restored the unit to usefulness. Total cost of the project was under $60 for both amplifiers. That includes all of the caps except the power supply caps plus all of the 2 and 3 watt 20% resistors being replaced with 5%.

What was not anticipated was the very obvious improvement in sonic performance. Difficult to impossible to describe the change. But at one point, I swore I could hear the pianist pounding the keys. Norah Jones, who in the past, has been a bit severe, we can now hear the subharmonics in her voice, I'd swear I could hear her breath. Overall, improved clarity, dynamics, sound stage. More small details that weren't there previously.

So in a nutshell. You do not have to use insanely priced exotic caps willed with fairy dust when replacing 40 year old electrolytic caps. Just choose wisely and do it.

Sorry I have not looked this section for some time... but I will now add some remarks I have found out when recapping some vintage amplifiers during few years, not too different Kent made.

First of all I have tried to retain original appearance as far as it has been practical. Modern caps are usually smaller than vintage ones, but usually replacing 50uf psu cap with 150uf cap does no harm to performance. Sometimes replacing axial does not look too good... but fortunately at least Nichon and Vishay/Spargue do produce axial caps even 105C ratings are scarce. Multi section caps and some can caps are hardest to replace with new ones. But... they can be restuffed with modern radials like I did to main reservoir of H/K Citation 11, as could not find original dia can cap to replace original one. Please look from pics enclosed.

I have used Elna Silmic´s and Nichon Muse audio caps to replace original signal coupling caps. For some reason I have figured that 105C low impedance should be used as power supply caps. 85C rating is usually more than enough for solid state gear and after all audio grade electrolytis do carry 85C rating anyway. However, main reason using 105C caps is that 105C rating usually can be achieved with low ESR and inductance figures. In tube amplifiers inside temperatures are usually 40-70C ... so 105C types are preferred... even ordinary 2000H 85C types may have 20 000+ H service life at 60C, as ripple currents from PSU are usually less than 50% from ratings.

Voltage ratings are quite straight forward when recapping single ended amplifiers like this Citation 11, as there is usually enough bias to keep caps in good condition for long time. However coupling caps are operating quite often in zero bias condition in amplifiers using dual rail power supplies. In original designs manufacturers usually make short cut and use cap (say 10uF/35V) for in PSU card for filtering 24V rail, same cap again for 15V rails and again for signal coupling, in position where it is impossible to produce more than 1V voltage across cap. 35V rated cap is perfectly OK for 15-24V duty... but similar quality cap with 6V rating will be living longer and happier life in position where it will never receive more than 1V across positive and negative terminal. Film caps are also good for such positions, but if more than 1,5uF capacitance is needed they will usually spoil the appearance being too bulky to fit the space scaled for electrolytic.

Other components seems to stand test of time quite much better and resistor failures seems to be associated quite often to other problems. I have also found that simple unexpensive recap and cleaning will give good second life for vintage amp or tuner. I will enclose some pics about my H/K Citation 11 rebuild I made few years ago. This Citation 11 was produced during last months of its approx 5 year production... but I traced 5-6 grounding errors in original wiring loom. It took more that 2 weeks to trace errors, but this paid off quite well. I managed to improve hum figures by 6-7dB and improve sound quality quite much too.

Best Regards

Kimmo

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Nice job Kimmo!

Regarding the multi-section can caps, if you look at my KLH Model Eight restoration booklet, attached to Post #1 here http://www.classicspeakerpages.net/IP.Board/index.php?showtopic=6387 go to pages 14-17 for discussion of "stuffing" cans and some other pointers.

Sometimes you can find the correct value NEW can caps at www.tubesandmore.com I now use their 4x50uF can caps to replace the 4x60uF caps in the Model Eight. No problem.

You can also sometimes get lucky on an electronic surplus site such as Nebraska Surplus Sales or Skycraft.

-Kent

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It is nice that CE Distribution decided to start manufacture some of the old Mallory twistlock capacitors. However there many old ones are still unavailable. When I needed 75uf+75uf/475V one for my ARC SP3 rebuild... closest one I did find was something like 100uf+100uf/525V, which was close enough, but so tall that it will not fit under the hood. Maybe I shoud use F&T 100+100UF/500V chassis mount cap and use some kind adaper ring to attach it on the PCB. In my ARC D76A rebuild I used radial and snap on caps as values like 600uf/350V and 200uf/350V were unavailable, and there were 14 pcs of twistlocks in total... total cost of twistlocks would have been something like 400 USD + delivery, duty& VAT of 24%.

Re "stuffing"... I have usually broken the phenolic terminal board and removed old cap from housing trough this opening. This way you do not need to cut housing into two pices. I have soldered new terminals to radial caps and used electrical tape to bundle caps and one straw together. After this I have placed this bundle in the can and sealed the surface with acrylic putty. After 2-3 days I cut this straw to flush with the surface... so it will act as safety vent. After finishing the surface with black marker pen... cap will look original enough for me.

As you say surplus caps are sometimes available at very atractive prices. But prices of surplus computer grade electrolytics have gone to insane figures on the ebay... I do not understand why I should pay premium for caps that are 20-30 years old stock compared to Mouser prices.

Best Regards

Kimmo

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  • 4 weeks later...
  • 2 weeks later...

Thanks for inspiring me to get back into my SAE amp. The bridge rectifier failed on one of the power supplies which I replaced. At the same time I replaced caps and resistors and ended up with 5-6 vdc offset :) oops .... It is not a particularly good amp design so I just sidelined it.

At the same time I am rather curious where I went astray. No schematic to be found on this model unless I get inspired to sketch everything out ... not sure it will be worth all the time involved though.

I am curious to do surgery on some of the old electrolytics to see just how much they have deteriorated.

Roger

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I am curious to do surgery on some of the old electrolytics to see just how much they have deteriorated.

Roger

I have to admit I had the same curiosity. unfortunately, I couldn't find my capacitor checker at the time and disposed of the old parts. In the case of my amplifiers, most are conected to the 100VDC rails. I do wonder if a low voltage meter would have detected the failed cap.

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