| K100-2 term question - trem strength fades [message #23042] |
Thu, 04 June 2015 21:56  |
gui_tarzan
Messages: 24
Registered: May 2015
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Junior Member |
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When I turn on the trem it sounds healthy, but after maybe 30 seconds it starts to get weak. Turning it off and back on makes it normal again but it gets weak again. I'm not real experienced with solid state circuit behavior (I work on mostly tube amps) so I'm reaching out for ideas. The reverb works fine, though it sounds kind of spacey cranked up. That could be the tank or just the nature of the beast, I'm not sure yet.
--Jim
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| Re: K100-2 term question - trem strength fades [message #23044 is a reply to message #23042] |
Fri, 05 June 2015 02:19  |
chicagobill
Messages: 2006
Registered: April 2003
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Senior Member |
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My guess would be that the oscillator starts out fine and then loses strength. If you have a voltmeter read the voltage at the intensity control. Compare the levels when it starts and when it dies down.
If the oscillator voltage at the intensity control reduces as it warms up, check for the voltage levels at the output of the oscillator and see if the voltage dies out there. You need to see if the problem is with the oscillator or with the coupling caps.
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| Re: K100-2 term question - trem strength fades [message #23045 is a reply to message #23042] |
Fri, 05 June 2015 06:22 |
stevem
Messages: 4774
Registered: June 2004
Location: NY
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Senior Member |
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Also all the small electrolytic caps like the 10uf ones or whatever should just get shot gunned and replaced in that part of the circiut.
If you have a thermal gun then check these caos that go to ground, and you check them when the amp is first on and then after the issue starts up you will likely find one running hot and this will be the one pulling down the power supply voltage which is making for the slow fad out deal.
[Updated on: Fri, 05 June 2015 06:26] Report message to a moderator |
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| Re: K100-2 term question - trem strength fades [message #23051 is a reply to message #23042] |
Fri, 05 June 2015 14:17 |
chicagobill
Messages: 2006
Registered: April 2003
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Senior Member |
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I don't have a problem with replacing all of the electrolytic caps in there, but I personally really want to know what the problem is before I start changing anything.
I like to test things as best I can until I find something that doesn't seem right. That will lead me to the probable cause of the malfunction.
Let's say that the problem here is a bad coupling cap that sends the LFO signal to the intensity control. Shotgunning the caps will fix the problem, but what if the problem is a leaky transistor that is pulling too much current causing the voltage to drop as it warms up? And every time you start soldering parts on any board you start to risk damaging things that were not broken to begin with.
Just my 2 cents.
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| Re: K100-2 term question - trem strength fades [message #23188 is a reply to message #23058] |
Tue, 23 June 2015 18:02 |
gui_tarzan
Messages: 24
Registered: May 2015
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Junior Member |
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So I'm looking at this board and I don't see any e-caps. Wait, I think I figured out that the dipped caps must be e-caps, they have 10-15 and a "+" above one lead. That's a new one on me.
Ah, it won't let me post a pic, I don't have enough posts yet. Sheesh.
--Jim
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| Re: K100-2 term question - trem strength fades [message #23203 is a reply to message #23042] |
Fri, 26 June 2015 13:40 |
chicagobill
Messages: 2006
Registered: April 2003
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Senior Member |
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If the hum is worse with no guitar plugged in, check the grounding of the input jacks and the grounding switch contacts on the jacks as well. For that matter, check the grounding of the pc board, the power supply, etc.
Is the reverb tank mounted with the output side as far away from the power transformer as possible? Is the tank the original one for the amp or could it have been replaced? There could be a ground loop caused by a wiring fault if the pc board jack wiring has been altered.
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| Re: K100-2 term question - trem strength fades [message #23204 is a reply to message #23203] |
Fri, 26 June 2015 14:08 |
gui_tarzan
Messages: 24
Registered: May 2015
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Junior Member |
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Everything was original until I replaced a handful of the e-caps as written previously. I tried the thump and tap tests but I haven't replaced the reverb cables yet. I didn't even seen any solder joints that looked like they had been touched since the factory did them.
--Jim
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| Re: K100-2 term question - trem strength fades [message #23206 is a reply to message #23205] |
Fri, 26 June 2015 20:35 |
gui_tarzan
Messages: 24
Registered: May 2015
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Junior Member |
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The amp sounds good now except for the reverb. It doesn't seem to be dropping out anymore but to put it bluntly, the reverb sucks. When it's all the way down it has a good tone and effect, but when you start turning it up it gets real muddy and quiet, like the dry signal is being turned down and the wet signal is being turned up real hard and fast. It sounds horrible. A different tank made no difference. The caps are just generic 10/35v electrolytics. My gut says it's not a cap just because it's not making any different noises than it did before, other than like I said it doesn't seem to be dropping out now.
--Jim
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| Re: K100-2 term question - trem strength fades [message #23207 is a reply to message #23042] |
Fri, 26 June 2015 21:45 |
chicagobill
Messages: 2006
Registered: April 2003
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Senior Member |
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That's exactly how Kustom amps are designed to work, The reverb control works as a balance control. Unlike other amps where the reverb is added to the straight signal, the kustom circuit reduces the amount of straight signal as it increases the reverb signal.
I don't know if there were any circuit updates to the reverb on that model, but there are two versions of the schematic on the board here. Take a look at the two versions and see if there were any changes to the reverb circuit and see which version you have.
You could change a few resistor values to reduce the overall amount of reverb going into the reverb control.
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