[DSK]

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

Andy, I had Hugh fit 10nF/400VDC Sonicap Platinums for me at C19 and C21 as part of my mods package. 

[andyr]

Andy, I had Hugh fit 10nF/400VDC Sonicap Platinums for me at C19 and C21 as part of my mods package. 

Thanks, Darren.  That's great! 

Regards,

Andy

[Builder Brad]

Cheers Gaeshin,

I have some plumbers flux that I know would clear off any muck before soldering, problem is I need a blow-torch to get the temps!

[Builder Brad]

Guys,

I just love the GK1!

I have already removed the input cap C1 and upgraded C21 to an off-board 2.2uf Hovland Musicap, by-passed with 0.22uf Audionote Paper in Oil cap. I guess there would not be a problem using the old C21 caps to replace the poly caps at C19, I think that they were 1uf Auricaps.

Brad

[gaetan8888]

Cheers Gaetan,

I have some plumbers flux that I know would clear off any muck before soldering, problem is I need a blow-torch to get the temps!

Hi Brad

Plumber flux are acid flux, it is not for electronic because of the acid in the flux.

Bye

Gaetan

[AKSA]

Brad,

1uF for C19 - the grid coupling cap - is FAR too big and may not sound very good.  Always use the smallest cap you can for best sound....  You really only need 22nF max, 10nF is fine.  The impedance of the grid at this point, calculated, is 4.3M, VERY high, so a tiny cap is all that is required.

Cheers,

Hugh

[jules]

Brad,

are you still using a 100N+? If so, it might be a good idea to upgrade C1 on that amp to a film cap, particularly if you've gone to the trouble of using a Hovland at C21 in the GK-1.

Have you solved the original problem yet?

jules

[Builder Brad]

Cheers Hugh,

problem solved.......with the 1uf cap!. It was on hand, so in it went, sorry Hugh. It does have quite an agressive sound now so I will swap this cap for something smaller. I think I can get paper/oil Hovlands down to 0.00039uf I guess that would be even better that the polystyrene caps that were originally in C19.

Jules,

good idea. I have 2x 100s 1 x 55 and 1 x 25, the 25 has the full N+ and the 55 has the N upgrade, so they both have upgraded C1 caps, however you are right about those AKSA 100s as they still have the standard .47uf input caps. I guess its also worth looking at changing the 55 and 25 input caps for something even better. Any sugestions on values, sources ect?

Brad

[jules]

Brad,

I think you'll get some major improvement by changing the C1s in all your amps. I'm using RTX relcaps at C1 in my 55N+ to replace the original BG. I'd suggest that 1.0uf with .01uF in parallel would be ok for the 55. You might go for something bigger with the 100, like 2.0uF [with .02uF in parallel]. I'd guess that .5uF [with parallel cap] would be enough for the 25.

There's plenty of options for brand of cap. You could go as far up as a V cap platinum or Sonicap platinum [see the earlier thread here on platinum caps for the GK-1] but since you're using the Hovland, it could work well to have the slightly different characteristics of the RTX to compliment it. You could use your 1.0uF Auricap as a test or for comparison. It's the right size.

Replacing C1 in my 55N+ has been one of the best mods I've made.

PS ... on tubes: If you leave your GK-1 on all the time it might be worth looking for some NOS Telefunken PCC88 valves. These have a filament heater voltage about 1 volt below the 6992/7308 valves. This gives an extended life on top of the already long lifespan offered by Teles. They are also relatively cheap [compared to NOS Siemens and Tele. 7308/6992] and give you another tool to tune the sound of your system. Telefunken and Siemens tend to be more accurate [clinical if you don't like them  ] while Amperex tend to be warmer [inaccurate if you don't like them  ].   


jules

[Builder Brad]

Cheers Jules,

lots to condsider, I will probably re-use the 1uf Auricap in the 55 and source a selection of other caps for the rst of the amps. You have got me tweaking again!

Brad

[jules]

You have got me tweaking again!

Excellent! I hope you get some good results.

Jules

[PSP]

I have really liked Mundorf Silver/Oil as an input cap in AKSA and Life Force amps.  You can read Jon L's Cap Comparison thread on Audio Central as I strongly concur with his assessment. 

A few months ago I put Mundorf S/O input caps into the LF55 driving the Orion midrange to extremely nice effect.  The midrange came alive, voices and strings (cellos in particular) more present.  I finally "get" what people are talking about when they go on and on about "the glorious midrange".

In the AKSA 55 that I use in the bedroom system (driving GR-Research Paradox-3s), the Mundorfs present the music--at least to my ears--in an absolutely holistic unified way.  The music just sounds right.  I love large symphonic works, and I have been tweaking for a long time.  IME, setting AKSA or LF C1 = Mundorf S/O would rank in the top half dozen most satisfying "keeper" tweaks I've done. 

Peter

[hanguy]

In the AKSA 55 that I use in the bedroom system (driving GR-Research Paradox-3s), the Mundorfs present the music--at least to my ears--in an absolutely holistic unified way.  The music just sounds right.  I love large symphonic works, and I have been tweaking for a long time.  IME, setting AKSA or LF C1 = Mundorf S/O would rank in the top half dozen most satisfying "keeper" tweaks I've done. 

Peter

Peter, what value do you use for the AKSA55 mod?


Mike

[Builder Brad]

Nice one Peter!

I can get those caps in the UK, made in Germany I think, The .47uf is £22, 1uf £39 and the 4.7uf is around £50. do those prices seem about right.

I may just use the 1uf out of the GK1 on the 55 for now. I also have a pair of 0.01uf V-caps spare that I may use on the ASKA25, although the value could be a bit low? supose I could use the v-caps in the GK1 to replace C19. options, options, options.

I also have a couple of spare 4.7uf SCR film caps that I could use on the 100s

Brad

[Builder Brad]

arghhhhhhhhhhhhhhh, that should do it actually ...................................argh hhhhhhhhhhhhhhhhhhhhhhh, no I dont feel any better........................... The noise is back!

I have just replaced C19 with 0.01uf V-caps and was looking forward to listening to the changes and also using the 1uf Auricaps that were liberated in the 55w AKSA, unfortunately the noise is back with a vengance, this time it is more regular, like continuous, only one channel is affected and there seems to be quite a bit of LF noise because the grills are really moving on the Orions. When I tap the tube with my finger I can get a crackle plus the noise, even when I am using the SS outputs I get a slight crackle.

I have swapped over the tubes without making any difference to the problem, which is a start, I guess, and have re-soldered all of the base pins. I must say that I am not completely happy with this as the solder does not seem to wick readily onto the base pins - HELP!

Brad

[AKSA]

Brad,

Does this happen with the GK1 completely out of the circuit?

We now know it ain't the toob......

It must therefore be the SS input stage.

This sounds like a poor connection, something mechanical, some corrosion or oxidation somewhere, look for a dry joint.

Both channels, or just one?

Hugh

[Builder Brad]

Hi Hugh,

The SS output is fine and only 1 channel of the tube out is affected. It must be one of the tube base joints. I have already re-soldered these and was not happy as the solder would not flow readily onto the base pins.

It was quite a job to remove the old solder from the base pins, I guess I will have to go back and do it again. This time I will use some seperate flux and see if I can get a better connection.

Brad

[gerado]

Hugh,

does anything go wrong with the tube sockets themselves? Is it worth replacing them?

Brad did you actually use plumber's flux in the end? Gaetan suggested this is not suitable because it has acid. Since the problem was briefly solved for a few days slowish corrosion from acid could be one reason why the  noise returned, though not the only.

Though unlikely, try wiggling the interconnect out of the GK as well.


 

[Builder Brad]

Cheers Gerado,

no, I definately did not use the plumbers flux, just a joke! but the pins of the base really do need something to really clean them. Its a good point about the actual sockets, mine are very loose and nothing like the sockets on other 9 pin tubes I have encountered. I would find it easier to replace at this point having already spent quite some time trying to clean up and resolder the current bases.

Brad

[AKSA]

Brad,

I think Theo might be right.....  I would consider replacing the tube socket.  It's a simple micenol Cinch nine pin, readily available in the US, sadly I've just run out of them, must get some more......

The tube sockets don't normally give trouble.  There's a product call Caig fluid which removes the oxidation from them;  it might work.  Another option is complete removal, then scraping with a knife and a bit of wet/dry paper on the metal of the pins.  I agree resoldering the pins is tricky, but it should be that bad, and that's why I suggest a new socket.

Are the pins OK on the tubes?

Hugh