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When is time to recap vintage amp?
When is time to recap vintage amp?
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Old 18th December 2013, 10:54 AM   #1
budkor is offline budkor  United Kingdom
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Default When is time to recap vintage amp?

Hello

I am wondering when would be the best time to recap my vintage solid state Kenwood amp. When opened the casing, and looked at the caps, they are not bulging or leaking anything that.

But when powering on, the sound is a bit crackling and popping for about 5 minutes, and it seems OK for the rest of the day.

The amp is from late 70s or early 80s, and has original parts. Would it be best just recapping now, or wait until further degrade of sound or function, and physical signs - bulging and leaking caps?

Thanks for your advice and info. cheers.
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Old 18th December 2013, 11:03 AM   #2
Mooly is offline Mooly  United Kingdom
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When is time to recap vintage amp?
Sounds like more than recapping is needed. Check for dry joints and intermitent failure (I seem to be saying this in many threads lately) of driver and VAS transistors.
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Old 18th December 2013, 11:09 AM   #3
968driver is offline 968driver  Belgium
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I think that "crackling and popping" sounds are not caused by electrolitic capacitors.
I suspect transistors or diodes.
Old elco's are not bulging, only newer types develop this rather recent desease.
I myself never change capacitors if there is no real problem.
As such, I do not believe in "recapping".
If there are not obvious problems, keep the item original!
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Old 18th December 2013, 11:19 AM   #4
budkor is offline budkor  United Kingdom
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The amp has been put away for a few weeks for the purpose of having a look inside again. I took it out, connected, have tried powering on again this morning.

It was not crackling and popping this morning, but the sound on one channel is very weak, and puffy for a while (say 2 -3 minutes), and then settles down. It is OK after that.
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Old 18th December 2013, 11:46 AM   #5
Mooly is offline Mooly  United Kingdom
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When is time to recap vintage amp?
Same advice applies. Only other to check is to make sure that controls and switches are OK and not in need of a clean. That should be fairly obvious though as they would respond to movement etc.
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Old 18th December 2013, 02:12 PM   #6
budkor is offline budkor  United Kingdom
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Ok - will get a bottle of servisol, and clean all the pots, controls and switches first, and see how it goes. So recapping is not needed urgently for this amp. Glad to know.

Many thanks Mooly and 968driver. cheers.
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Old 18th December 2013, 04:11 PM   #7
Mooly is offline Mooly  United Kingdom
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When is time to recap vintage amp?
If the switches and pots need cleaning then that should be fairly obvious as the crackling will come and go as the switch/pot is moved.

If the crackling happens with the volume control turned down then its more than likely a faulty component in the power amp.

Remember that these kind of faults can suddenly become permanent putting a large DC offset across the speaker blowing that and the amp.
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Old 18th December 2013, 04:23 PM   #8
budkor is offline budkor  United Kingdom
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This happens first time when it is powered on in the day.

When volume is turned up and down, sound from one channel appears and disappears like kind of fading.

After about 10 minutes powering up and playing music, from then on, it is OK for the rest of the day.

When volume is turned down, it is absolutely quiet all time.

Last edited by budkor; 18th December 2013 at 04:35 PM.
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Old 18th December 2013, 04:36 PM   #9
Frank Berry is offline Frank Berry  United States
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I would certainly replace every electrolytic capacitor in the amplifier. After 30+ years, it's certain that they have dried out.
The silicon grease (heat sink compound) under the power transistors is probably dry too.
You should remove all transistors which are mounted on the heat sink (one by one), scrape the old silicon compound from the transistors, mica insulators and the heat sink(s). Apply new silicon compound and re-mount the transistors.
This will take some time. If you value the amplifier, it's time well spent.
After doing the above, if you are still having issues with the amplifier, you should be able to trace the noise using 'freeze spray' to localize the problem.
Have fun ... and take your time!
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Old 18th December 2013, 04:41 PM   #10
Mooly is offline Mooly  United Kingdom
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When is time to recap vintage amp?
If its quiet with the volume turned down then it sounds like the problem is in the preamp section... which could be switches and pots needing a clean. Small signal stuff is low powered and usually pretty reliable. Does it matter what input is selected ?

You need to make a start and see what you find.
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