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  #1  
Old 31st October 2011, 05:17 PM
HighFidelityGuy HighFidelityGuy is offline
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Default KEL84 clicks and pops from right channel?

Hi,

At the beginning of the year I purchased a second hand KEL84 that was already complete and working but was an early version. I decided that I liked the sound quality but felt it could be improved by upgrading various components and implementing the various improvements that were made to the design over the years. So I proceeded to strip the whole thing down and repopulate the board with boutique components including higher wattage resistors and Schottky diodes etc. The amp worked perfectly afterwards and I felt the sound quality had improved.

Over the last six months or so I've gradually experimented with different valves and cables and during this time the amp has continued to work perfectly. Then about a week ago I started to get clicks and pops from the right speaker. These sound very similar to what you get from a scratched vinyl record. I've tried lots of things to narrow down the source of these including disconnecting the KEL84 from my preamp, swapping power cables, valves, speaker cables, speakers etc. So I've come to the conclusion that something is wrong with the amp it's self. I've had a look inside the amp and can't see any obvious signs of failing components. So I'm hoping someone can shed some light on what could be causing this issue or give me some guidance on what tests to perform inside the amp?

Many thanks,

Dave.
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  #2  
Old 1st November 2011, 09:11 AM
Richard Richard is offline
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Default Re: KEL84 clicks and pops from right channel?

Hi Dave,

This is often due to poor valve pin connections of the small signal valves, small valves gone noisy, or a dry solder joint on the input end.

I've had it after installing NOS valves with oxidised pins. It sounded quite bad but they just needed a clean (I used a glass fibre pencil from Maplins on the pins).

Sometimes valves just go noisy with age and need changing.

Also try swapping the valves across channels to see if the fault moves with the valves. If the noise strays put in the R channel look for a bad joint, check along the input signal wiring and valve base soldering. Past that let us know it may be a failing cathode bypass cap.
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  #3  
Old 1st November 2011, 03:44 PM
HighFidelityGuy HighFidelityGuy is offline
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Default Re: KEL84 clicks and pops from right channel?

Hi Richard, thanks for the advice.

I've tried swapping the input and output valves between channels and between different makes of valves. All the valves I've tried only have a few hundred hours on them. I've also tried cleaning the valve sockets and valve pins with Deoxit. Non of that helped and the noises remained on the right channel. I then had another look inside the amp and noticed that there was some flux residue around the valve socket pins on the underside of the PCB. So I cleaned that off and gave the rest of that side of the board a good clean at the same time. That's also not helped. As far as I can see all of the solder joints are still good as well.

So the only things I can think of now are that there is some flux residue on the other side of the board that's creating a high resistance joint, a component is failing somewhere or perhaps a valve socket is failing inside where I can't see.

Do you have any other ideas and what do you think I should check next?

This is really starting to frustrate me now as I was just starting to get happy with the sound I was getting from my system.
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  #4  
Old 1st November 2011, 04:09 PM
HighFidelityGuy HighFidelityGuy is offline
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Default Re: KEL84 clicks and pops from right channel?

Another thing I noticed after trying the above was that a couple of minutes after turning the amp on (and before and clicks of pops had occurred) a very slight fizzing/rustling noise came from the right speaker. I could only just hear it by putting my ear right next to the tweeter. This lasted a few seconds. Then after another couple of minutes some clicks and pops kicked in. I don't know if that info is of use but I thought I'd mention it just in case it rang a bell.

Here's some photos of the amp I took earlier in the year during the refurb and testing: http://s2.photobucket.com/albums/y48...0/Hi-Fi/KEL84/
I've since tidied up the internal wiring a bit. The password on the album is "valves".
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  #5  
Old 1st November 2011, 08:28 PM
Richard Richard is offline
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Default Re: KEL84 clicks and pops from right channel?

Hi Dave,

Well, clicks and pops sounds like it could be interference so worth bearing in mind if you can tie that up with light switches or thermostats switching.

Check the faq,
http://www.world-designs.co.uk/forum...read.php?t=135
for the small valve anode resistors R10, 11, 12, 13. I had that problem of anode resistors breaking down and it starts as rustling and popping so change them first if you didn't already do it.

Past that, more soldering of all the joints on the R channel. Then component-wise the cathode bypass caps, C6,7, 12. 13, 14, 15 would be next for me.
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  #6  
Old 1st November 2011, 09:50 PM
HighFidelityGuy HighFidelityGuy is offline
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Default Re: KEL84 clicks and pops from right channel?

Hi Richard,

Thanks for the advice.

I've ruled out most things that could be causing interference like my Wi-Fi and mobile phone but I've not tried turning off my land line cordless phones, so I'll give that a go. As far as mains noise goes, I don't think that's the source as I've tried running the amp off two different filters and also had a Belkin noise sniffer running all day. The sniffer makes a noise whenever it detects crud on the mains and although it made a few noises now and then, none of them ever coincided with noises from the right speaker.

None of the components can be breaking down due to age as I literally replaced everything with brand new replacements at the start of the year. However that's not to say that something hasn't failed due to a manufacturing defect. So I guess I need to start checking component values to see if anything has drifted. I know that all the caps and resistors had spot on values when I started as I tested every single one before and after installation to make sure I hadn't over heated anything. I also read the info in the faq about the resistor wattages needing uprating so I used 2W Kiwame carbon film resistors all round except for the ones that I upped to 12W Mills wirewounds (cathode/anode) and a couple of tantalums where I couldn't get the right value Kiwame. All the resistors and diodes were spaced away from the PCB to allow better air flow. I even soldered the grid resistors directly to the valve bases to ensure they were as close as possible.

I'll dig out my DMM and start testing. I'll let you know how I get on.

Cheers,

Dave.
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  #7  
Old 2nd November 2011, 09:11 AM
bob orbell bob orbell is offline
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Default Re: KEL84 clicks and pops from right channel?

Dave, been following your thread and I do agree with Greg's comments, may be a little harsh, but true, I have just fixed a PRE3 and PHONO3S for a member and his soldering was bad, but it was his first attempt, I am shure he took on board my advice and feel you should take Richard's advice. Go over all your valve pin connections with quite a hot iron and flux and flow the solder through both sides of the board, this is most likely to be the problem, have a look before and after with a magnifier, it may suprise you. BOB
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  #8  
Old 2nd November 2011, 10:18 AM
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pre65 pre65 is offline
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Default Re: KEL84 clicks and pops from right channel?

A good magnifying glass is a boon for spotting soldering errors.
__________________
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Everything in this post is my honest opinion based on what i thought I knew at that very moment in time.
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  #9  
Old 2nd November 2011, 11:14 AM
Richard Richard is offline
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Default Re: KEL84 clicks and pops from right channel?

Yes, the other way forward is to try and provoke it.

Up-end the amp with it securely supported and connected in-system. Fire up and carefully prod/flex the pcb and input wiring with a plastic knitting needle or similar trying to get it to make the offending sound.

I sorted one of these same amps many moons ago by this method but even then only nailed it down to an area of a dozen or so possible joints which I re-soldered and bingo it was fixed To the naked eye it did look a good soldering job by the original builder too. So we have to accept there is a fault and start over...
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  #10  
Old 2nd November 2011, 11:33 AM
HighFidelityGuy HighFidelityGuy is offline
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Default Re: KEL84 clicks and pops from right channel?

Thanks for your input everyone. I'm not sure why some of you have got the idea that I'm not following advice as I think I've clearly stated that I've tried most things that Richard has suggested, other than the re-soldering. I meant to say in my last post that I was going to do that but I forgot, so I apologise for that. I guess I concentrated too much on listing all the things I've tried. I'm trying to be as thorough as possible.

Please be assured that I am taking on board your greatly appreciated advice and that the next things I'm going to try are re-flowing solder joints and testing component values. I didn't have time to do that yesterday.
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