Klark Teknik KT-2a making crackly noise after not being used for a few months?

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Klark Teknik KT-2a making crackly noise after not being used for a few months?

Post by dickiefunk »

Hi,

I've got a Klark Teknik KT-2a compressor which I really like. However, it has started to make a lot of crackly noise after not being used over the past few months?

Here is an audio clip of the noise I mention :-

https://drive.google.com/file/d/1WRhF5g ... sp=sharing

I'm wondering if this noise is condensation on the tubes or something else?
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dickiefunk
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Re: Klark Teknik KT-2a making crackly noise after not being used for a few months?

Post by Wonks »

I don't think you'll get any condensation forming in this weather, unless you keep it in the bathroom. And moisture doesn't affect valves like that.

It sounds to me like it could be a valve itself that's on the way out. But it could also be corrosion on the valve pins/valve base, or a loose ribbon cable (if there is one) or even a dirty pot.

But probably a valve. You've got 12AX7, 12BH7 and EL84 valves in there. (I think the EL84 is probably used to replace the 6AQ5A valve that was in the original). Any of them could have lost vacuum. Sometimes it happens. You could look for signs of overheating (the valve lettering is normally red and goes white if it gets too hot) or a white residue inside the valve itself (lost vacuum). But leave the unit disconnected for a full day before opening it up as it's got big capacitors (a couple of 40 uF caps in the power supply circuit if its like the original) and I think runs at around 350v DC internally.

Unfortunately with 3 different valve types and 3 valves you can't swap them around to see if things improve. You could try removing and reseating each valve in turn.

I'd also exercise all the pots and switches for a few turns/operations each, which should clear any light dirt away.

Web reports seem to indicate that these things run quite hot, so is it in a well ventilated space in your rack, ideally with nothing directly above and below to allow for ventilation? Running too hot will reduce valve life.

Unfortunately valves are rather scarce at the moment and have shot up in price as a result, so it won't be a particularly cheap job to get a replacement valve of each type to try out. At least EL84s are some of the least expensive power valves around.
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Re: Klark Teknik KT-2a making crackly noise after not being used for a few months?

Post by Wonks »

What's the warranty on them? I've seen 10 years mentioned in some places but that could vary from country to country. If still under warranty, you may be able to get it checked out free of charge, but valves will be probably regarded as consumables with no minimum life expectancy (though an immediate failure should be dealt with).
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Re: Klark Teknik KT-2a making crackly noise after not being used for a few months?

Post by dickiefunk »

Thanks for the suggestion. I upgraded the valves in the KT-2a to Harma Retro tubes from Watford Valves. They are only around 18months old hand have had light use. I still have the original Bugera tubes so I’ll be able to swap the tubes out to see if that’s the problem.
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Re: Klark Teknik KT-2a making crackly noise after not being used for a few months?

Post by Wonks »

That’s good. One at a time would be ideal but I don’t know what the internal construction is like and whether you can change a valve without risk of touching any of the circuitry. It’s often possible to on valve amps, but with more compact equipment, there isn’t always the space for protective barriers.
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Re: Klark Teknik KT-2a making crackly noise after not being used for a few months?

Post by resistorman »

First thing I always try with valves is cleaning the pins. Sometimes even just pulling then reseating will fix spurious noise. I use a pen dispenser of deoxit on the individual pins, or you can use a bit of spray on a lint-free cloth. You don't want an excess of liquid!
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