| K200 B4 [message #26801] |
Tue, 17 July 2018 23:08  |
sskydiver1
Messages: 27
Registered: December 2008
Location: Texas
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Junior Member |
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I plugged in my K200B4 tonight for it's 90 day workout (wish I had time to play it it more often!) -
and I was hearing way more way more of the "white noise" (which in retrospect may have been 120v hum) than usual.
I went ahead and started playing through it and checked out all the functions, which all seemed to work - and the volume was as loud as usual.
I did notice that when I switched the "Selective Boost" knob it was making quite a loud popping noise when switching positions - but the frequencies were changing as they should.
Within 5 minutes, the amp volume dropped WAY down and the white noise/hum went away. You could still hear the guitar - but the volume was low bedroom volume at best. All the amp functions still seemed to work just fine, but no volume so to speak. When I used my flashlight to look at the back I saw a little smoke and turned the amp off right away.
Also - at the new very low bedroom volume - the amp gets very distorted as if there is a fuzz box on it when you turn the volume past halfway (I turned the amp on again to see if anything had changed - which it hadn't)
Any thoughts? Wondering/hoping it might be a part I could install with my intermediate soldering chops - and if not - can anyone recommend a tech who could fix her up and keep her going? I am hopeful that it is not TOO big an issue - it would be a shame to let this amp go into the scrap heap of history.
Final question - is this something that a good electronics and amp tech can fix - or do you need very specific experience and rare parts to fix it?
Many thanks for any response!
Derek
[Updated on: Tue, 17 July 2018 23:27] Report message to a moderator |
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| Re: K200 B4 [message #26802 is a reply to message #26801] |
Tue, 17 July 2018 23:51  |
chicagobill
Messages: 2006
Registered: April 2003
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Senior Member |
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Sorry to hear that you have a problem. Are both channels weak or just one?
If both channels are weak, the problem is either in the power supply or in the power amp sections. If only one channel is weak then the problem is probably in the weak channel's preamp section.
These amps a fairly easy to repair, and with the exception of the driver transistors on the power amp board all of the parts are easily replaceable.
The good news is that if it was something really bad, the fuse would have blown and the amp wouldn't power up. The bad news is that there is something wrong that will require some investigation in order to fix it.
It can be fixed, so don't even think about trashing it. Good luck.
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| Re: K200 B4 [message #26804 is a reply to message #26801] |
Wed, 18 July 2018 12:20 |
chicagobill
Messages: 2006
Registered: April 2003
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Senior Member |
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No, any tech that can fix a solid state guitar amp should have no problem in fixing your amp.
The basic power amp design is a tried and true circuit that has been around since the 1950's. It is still used today by many companies for their guitar, bass and pa amps. The only difference is that the transistors are modern production units that are still being made today. So if they have fixed Peavey or Behringer or Fender transistor amps, they can fix your Kustom.
Remember that if they need schematics they can be viewed here in the technical section of the site and if they need technical help we can try and help them here online.
As for specific parts, don't worry about replacements until you know what the amp needs. The driver transistors can be replaced with modern equivalents. They just need a little coaxing to get them mounted in place of the old ones.
Maybe someone here can help recommend a tech in your area. I don't know anyone in Texas, but there must a few good ones somewhere there.
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| Re: K200 B4 [message #26809 is a reply to message #26807] |
Thu, 19 July 2018 14:23 |
sskydiver1
Messages: 27
Registered: December 2008
Location: Texas
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Junior Member |
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So Chicagobill and all -
More news to report.
The sudden drastic drop in volume was due to this:
I BLEW the speaker.
It is ripped from the basket almost all the way around - and I'm sad to report it was a vintage 1959 Jensen Alnico that I had used many times to test amp heads without issue.
I am 90% positive that I blew the speaker by turning the Selective Boost switch at loud volume - which was making a hell of a pop when "changing frequencies" (as this is what the switch does).
Lesson learned: Don't do that! Just moving the dirty switch (which obviously needs some contact cleaner) at low or no volume cleaned it up well enough to minimize the popping.
So I plugged the K200B4 into a different cab and it works fine-ish EXCEPT:
It has a lot more of the inherent white noise than another basic K200 I have in my collection.
I reviewed earlier posts from you in response to a similar issue Bill -
Does that sound like a bad cap to you? It is definitely the same basic "White Noise" hum as the basic K200 but at least twice as loud as the other K200B4.
Finally - is my research at all correct that the speaker output from the K200 head is 4ohm?
Many thanks again Chicagobill
Derek
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