[Builder Brad]

Help,

I have noticed recently that occassionally my Audio system would make some strange noises. I have issolated the source of these noises as the GK pre-amp. The most frequent noise that I am hearing is similar to the power up noise that your hear in metal casework when you power up large EI core transformers, only this comes out of the speakers, its not that loud but Ive noticed it now and I tune into it every time it hapens which is every 10 - 15 ninutes. I though that it could be something switching on or of elsewhere in the house but there is nothing that comes to mind and the GK1s Transformers should filter most of this out. The other sound is a low base kick that occurs maybe a couple of times an hour, or less.

Does anyone have any ideas?


Brad

[AKSA]

Brad,

I'm sorry this reply is so late - I've been away, and only picked it up just now.

Try taking the output from the sub-woofer rather than pre-out.  This will bypass the tube section, and if the problems persist, you will know it's in the SS section.  If the problem vanishes, then it's in the tube section.....  once you know, return to the forum and we will take it from there.

Hope this is helpful,

Cheers,

Hugh

[Builder Brad]

Cheers Hugh,

No problem with the delay, I only check the messages occassionally and have 100% confidence that you work this through for me.

I have now switched to the SS output only and the strange noises have gone!

What do I hit? and how hard?

Brad

[AKSA]

Hi Brad,

Hmm, take out the tubes, both of 'em, clean the pins carefully with a bit of steel wool, insert them afresh, twiggle them around a little to get good contact, and the problem SHOULD be gone.....

It is the gradual buildup of metal oxide on the pins and socket due to heat cycling.  They get damn hot, and require periodic cleaning.  Common problem with tubes.

Cheers,

Hugh

[gerado]

Hi Brad
 

my GK was making noises, different character to yours and in one channel. Initially it would go away by tilting the tube on that side into the socket but after a while this fix stopped working.
I finally traced it to a poor solder pin under the tube socket. Yours is both sides but you never know!
T

[andyr]

It is the gradual buildup of metal oxide on the pins and socket due to heat cycling.  They get damn hot, and require periodic cleaning.  Common problem with tubes.

Cheers,

Hugh

OK, Hugh ... easy to clean the tube pins with steel wool or emery paper - but how the hell do we clean the sockets!!??

Methinks some bright spark needs to invent some "emery toothpicks"? 

Then again, my sockets are gold plated ... so mebbe they don't need cleaning?

Regards,

Andy

[AKSA]

Do some tube breeding......  press it into and out of the socket four or five times.  That'll remove most of the oxidation.....

Kapitz?   

Hugh

[andyr]

Do some tube breeding......  press it into and out of the socket four or five times.  That'll remove most of the oxidation.....

Kapitz?   

Hugh

Yeah, Baby! 

Andy

[Seano]

Do some tube breeding......  press it into and out of the socket four or five times.  That'll remove most of the oxidation.....

Hugh......tsk,tsk.....you are letting your brethren down.  The solution must be far more complicated than that and involve some mystery product that costs hundreds of dollars per treatment.  Shame on you 

[AKSA]

Ah, Seano,

You have uncovered my contempt for BS - there is so much of it, huh?

Hugh

[Builder Brad]

Well,

I have now performed the cleaning and mating ritual with the tubes and........the sound quality is back, even though I had not noticed the gradual drop off, however the strange noises are still there.

I must say that I only had 1200 wet and dry paper which may be too fine. I did clean up each pin and removed the slight discolouration/ oxidation with a little effort.

After playing the GK through the SS section for almost a week I am now able to really hear the colouration that the tubes add to the music, a really pleasant ripple of energy woven into every note with vocals jumping right out at me. I am not even on the beer tonight!

Brad

[AKSA]

Hi Brad,

After the mating ritual you have to apply the heat.....

Resolder all tube socket pins to the pcb.  Take care not to overheat things, remove the tube first of course, and clean up with a sharp metallic pig sticker after then with a nailbrush and methylated spirit.  Allow to dry, and then put some electronic lacquer over it all, covering the tube socket when you apply it.

This should do it.  As posted by Gerado (thanks Theo!), tubes get REAL hot, and over time this dries out the solder joints beneath the socket.  Not much you can do about this unless you blow cooling air across the base of the tube, not something which is really necessary.

I'm glad you like the coloration of the tube.  That's definitely what they do best....

Cheers,

Hugh

[Builder Brad]

Cheers Hugh,

I thought that the act itself should generate enough heat!

Is it best to wick away the existing solder, or can I get away with a little more solder and flux?

Just a thought, I may look at making up a plug and cables with a seperate pcb for the tubes, which could then be placed for better ventilation, ie outside the case, the way you recomended in the build manual. I will also find it easier to service this dry solder joint thing in the future as I could make up a couple of spare cables, pcbs and tube bases which would just be swapped out.

Brad

[AKSA]

Brad,

It is a good idea to replace the existing solder by removing it before resoldering either with a sucker or solder wick.  The dry joint problem permeates the entire blob, in fact, so replacement is called for.

If you decide to mount the tube remotely, with jumper wire between the socket and the pcb, be very sure to make these wires no more than two inches, because the additional parasitics introduced could lead to instability - a common problem, particularly in the grid circuit.

Unfortunately you have highlighted why the GK1 was designed and laid out as it was - layout is quite crucial.

Cheers,

Hugh

[Builder Brad]

I have now resoldered the tube bases. This was a bit of a crap job, as the solder had really dried out and would not readily wick away. I used a combination of solder wick and a sucker to get clear joints. The flux that was impregnated in the wick that I used seemed to work better at cleaning the joints when I could get it to work than the roisin flux in the new solder I used.

I am not 100% confident of the work and the noise is still there, on 1 side. Its not the tubes as I have swapped them over. Looking at the base connections they are really tarnished and I found it difficult to get solder to flow, I wonder how bad the connection is in the actual pin socket - the tubes do feel loose and nothing like some of the other tubes I have removed in the past, could the problem be in the actual socket?


Brad

[gaetan8888]

Hello Brad

Wen I have to solder heavily tarnished or oxidised connexions or tab I use separated Kester rosin flux, puting a bit of flux on the contacts before using the soldering iron and the solder, I find that more efficient than the flux included in the solder.

In worse case, wen separated rosin flux do not work, there is chemical to clean hard to clean tarnished or oxidised connexions before soldering.

If you have access to a Dremel with a miniature narrow bross you can use it with care to take out the oxidations in the tube pin socket, or you can also use a tiny minature files to clean the sockets.

Bye

Gaetan

[AKSA]

Brad,

After this work, I'm doubting that the problem lies with the tubes or the sockets.

It could be the grid coupling cap.  These caps, if overheated during soldering, will eventually fail, giving the symptoms you describe.

Polystyrene caps are highly sensitive to heat, and their failure mode is erratic, and in this case they have about 45 volts across them, so they are electrically stressed.

My suggestion would be to replace it with a high quality filmcap, and see if that fixes it.

Hope this helps,

Hugh

[Builder Brad]

ahhhhhhh

Not the first time either, as a result I have a bag of 20, or so, of those caps. If I remember correctly I should see a couple of volts on the volume pot if this cap is failing.

On a +ve note I think I have just sourced a couple of Amprex 7308 tubes, one of those late night quick hit fixes. I convinced myself that it MUST be the tubes as the GK1 has been on every day since 04/05.

Brad

[gerado]

Im a little disappointed in you Hugh!
The fix is simple and you let an opportunity slip by.

Bin the noisy unit and sell a new one   (Just joshing )

But then again its never been you style has it
 Let us know what the fix turns out to be and hope you find it soon.

[andyr]

It could be the grid coupling cap.  These caps, if overheated during soldering, will eventually fail, giving the symptoms you describe.

Polystyrene caps are highly sensitive to heat, and their failure mode is erratic, and in this case they have about 45 volts across them, so they are electrically stressed.

My suggestion would be to replace it with a high quality filmcap, and see if that fixes it.

Hi Hugh,

Is this C19 (10nF polystyrene)?

I happen to have a pair of 10nF Sonicap Platinums that I had bought for, but didn't use in, my external phono stage recap.  Would these be a good substitute for the polys in the GK-1?

Thanks,

Andy