| K250-1 bass head interference [message #29701] |
Sun, 08 March 2026 16:14  |
majikthise
Messages: 1
Registered: March 2026
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Junior Member |
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I bought my K250-1 about 20 years ago and used it regularly for about 10 years. Now after 10 year storage I get interference, depending on the bass I use and my position and bass direction in relation to the head. It's certainly something that the amp emittes and is picked up by the bass. Same thing with both inputs on both channels but if I turn the volume down on the bass it goes away. Also if I point the bass to a certain direction, the noise goes away. My active bass picks up hardly any noise. My passive basses, which are ok with other amps, pick up a lot. The noise is kind of high pitch rattle/whine.
I replaced the filter caps since that was easy and cheap and they were close to 60 years old. This might have helped little or so I imagine. However most of the problem still exists.
I can do repairs myself but I also have no problem to take the amp to a shop. Problem is most shops mainly deal with tube amps and probably do not really know these solid state units that well.
Any ideas on how to proceed?
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| Re: K250-1 bass head interference [message #29707 is a reply to message #29706] |
Thu, 12 March 2026 13:46  |
stevem
Messages: 4902
Registered: June 2004
Location: NY
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Senior Member |
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Ok, bad or weak filter caps produce a 120 hz hum in the audio output and there are other electrolytic filters in the amp that should get replaced after 60 years also, I will cover these in a bit.
If the noise here hearing is more like a buzz then here’s what to check.
The interconnecting cable in these amps have Molex type connectors on them.
These have Aluminum pins in them that get tarnished up with age and
That makes for bad connections .
Get to an automotive supply store and pick up a spray can of electromotive cleaner.
Unplug each connector and spray them out, while wet plug and unplug them a few times.
And then see how the amp plays .
I have had bad solder connections on the circuit board with the pins also so look over the bottom Of the boards.
In terms of the other filters in this amp these are small ones
On the power amp board alone there is a 33uf @ 10 volt. A 1uf @ 35 volt, and a 27uf @ 35 volt.
All of these types you find on any circuit board should get replaced ..
Last on the list of things to do is to reenforce the two front switch’s so they don’t break.
With age the plastic shank of these switches dry rots and they get brittle and can break.
If you take a tie rap and place one on each side of the switch to keep it pulled up against the metal bracket then it can’t break when the button is pushed harder then need be.
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