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K150-8 Loud Thump [message #26066] Thu, 20 April 2017 09:34 Go to next message
ReverbJoe is currently offline  ReverbJoe
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Registered: October 2012
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Hi guys, some time ago I had asked about a few things I thought needed fixing in my K150-8 combo, and I was told I might need two new power supply rail filters. I was suggested that because when I turn on the amp, it makes a loud thump after a few seconds. So I was hoping you guys could tell me what these power supply rail filters look like. Or where they are locates in the amp. Thanks in asvance.
Re: K150-8 Loud Thump [message #26067 is a reply to message #26066] Thu, 20 April 2017 11:16 Go to previous messageGo to next message
stevem is currently offline  stevem
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Registered: June 2004
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Please re-evaluate / check your statement of " makes a loud thump after a few seconds " a light turn on thump heard just as the panel lamps come on when turning the amp on is normal, other then that you may have some of the smaller Tantalium electrolytic caps in the amp going bad which could make for un-even power up of the output stage.

This could make for a D.C. Voltage on the output which would make for a late loud thump.
Re: K150-8 Loud Thump [message #26069 is a reply to message #26067] Fri, 21 April 2017 13:30 Go to previous messageGo to next message
ReverbJoe is currently offline  ReverbJoe
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There is a loud thump when turned on, so that is probably what you refered to. I did notice that there is thump when turned on. Is that also normal?
Re: K150-8 Loud Thump [message #26072 is a reply to message #26066] Fri, 21 April 2017 15:37 Go to previous messageGo to next message
stevem is currently offline  stevem
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Yes, and the better and bigger your speakers are the louder the thump will be!
It's when you do not hear a turn on thump that is a sign that the two main rail filters are taking longer then normal to charge up .

[Updated on: Fri, 21 April 2017 15:39]

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Re: K150-8 Loud Thump [message #26073 is a reply to message #26072] Fri, 21 April 2017 18:30 Go to previous messageGo to next message
ReverbJoe is currently offline  ReverbJoe
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I installed a new pilot light and noticed that it turns on and off while the amp is on. Is that normal?
Re: K150-8 Loud Thump [message #26074 is a reply to message #26066] Fri, 21 April 2017 23:44 Go to previous messageGo to next message
chicagobill
Messages: 2005
Registered: April 2003
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No, when the amp is on the pilot should stay on until the amp is turned off.

Check to see if the bulb is not correctly seated in the socket or the socket might need to be cleaned.
Re: K150-8 Loud Thump [message #26075 is a reply to message #26066] Sat, 22 April 2017 06:01 Go to previous messageGo to next message
stevem is currently offline  stevem
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I think he means that the lamp brightness goes up and down , but not fully out when playing, and that is normal .
The louder you play the more the lights will dim down!
Re: K150-8 Loud Thump [message #26076 is a reply to message #26066] Sat, 22 April 2017 10:46 Go to previous messageGo to next message
ReverbJoe is currently offline  ReverbJoe
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Actually, the light completely turns off and turns back on. I can hear the hum of something running when the light is on, and then the hum dissappears when the pilot light is off. I will try cleaning the socket and re-installing the pilot light.
Re: K150-8 Loud Thump [message #26077 is a reply to message #26066] Sat, 22 April 2017 12:17 Go to previous messageGo to next message
chicagobill
Messages: 2005
Registered: April 2003
Senior Member
If the sound stops when the light goes off, then the amp might be turning off when this happens. You might have a loose connection in the ac wiring, like to the thermal shut off switch.

Be careful when checking those connections, make sure the amp is unplugged and off before touching anything.
Re: K150-8 Loud Thump [message #26079 is a reply to message #26077] Sat, 22 April 2017 17:11 Go to previous messageGo to next message
ReverbJoe is currently offline  ReverbJoe
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I want to replace the old cord with a three prong cord, to see if it will fix anything. I have one that says 300 volts, is it good enough?
Re: K150-8 Loud Thump [message #26080 is a reply to message #26066] Sun, 23 April 2017 06:14 Go to previous messageGo to next message
stevem is currently offline  stevem
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From what you have posted up now , and like Bill has commented on you may have a bad AC connection in the amp, or it could be your power cable on the amp.

A grounded power cable will not fix anything , but it will keep you from getting a shock when touching another item of gear, in fact since your are deactivating the polarity switch when doing this Mod if you are plugged into a grounded outlet which is not grounded ( as in a new outlet in a old wired House) you will not beable to get rid of the ground buzz you may have .

Before you do anything new power cord wise see if you can get the power cord grommet out from the rear of the amp with a real big Ass Needlenose plier, as if you do not have the special made tool to do such this is the only way to get that grommet out.

What I do for a new cord when I want to keep a long one on the amp I head out to the hardware store and buy a small diameter extension cord and just cut the end off.

The potential issue with this is that many times these cables are a bit thicker than the original cord.

In a case like this a carefully slice some off the cords jacket down with a brand new single edge blade.
If you do not want to mess around like that and can live with a 6 ft cord then just use a IEC cord which you likely already have tons just sitting around the house!

[Updated on: Sun, 23 April 2017 06:16]

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Re: K150-8 Loud Thump [message #26083 is a reply to message #26066] Mon, 24 April 2017 06:52 Go to previous messageGo to next message
stevem is currently offline  stevem
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Registered: June 2004
Location: NY
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You may also have a bad fuse, if you have a clip lead then jump it out and check the results.
Re: K150-8 Loud Thump [message #26086 is a reply to message #26083] Mon, 24 April 2017 11:27 Go to previous messageGo to next message
pleat is currently offline  pleat
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Location: Belding, Mi
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I had a K50 that had a hum when the wrong bulb was installed. Playing hard the bulb would dim a bit and of course you couldn't hear any hum over the guitar. I replaced the wrong bulb with the correct bulb and the hum was gone. I'm sure the circuits are different but a quick check of the bulb or just remove the bulb to see if the hum is gone.
pleat
Re: K150-8 Loud Thump [message #26087 is a reply to message #26066] Mon, 24 April 2017 12:16 Go to previous message
stevem is currently offline  stevem
Messages: 4738
Registered: June 2004
Location: NY
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The K 50s and 25 models carry the lamp voltage in far more hum prone section of there circuit boards then any other Kustom model, so in light of this I do not think that having a wrong higher current pulling bulb in stalled in a K150 will do much.
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